Linux 4.19.133

[linux/fpc-iii.git] / drivers / i2c / i2c-core-base.c

/*
 * Linux I2C core
 *
 * Copyright (C) 1995-99 Simon G. Vogl
 *   With some changes from Kyösti Mälkki <kmalkki@cc.hut.fi>
 *   Mux support by Rodolfo Giometti <giometti@enneenne.com> and
 *   Michael Lawnick <michael.lawnick.ext@nsn.com>
 *
 * Copyright (C) 2013-2017 Wolfram Sang <wsa@the-dreams.de>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 */

#define pr_fmt(fmt) "i2c-core: " fmt

#include <dt-bindings/i2c/i2c.h>
#include <linux/acpi.h>
#include <linux/clk/clk-conf.h>
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/gpio/consumer.h>
#include <linux/i2c.h>
#include <linux/i2c-smbus.h>
#include <linux/idr.h>
#include <linux/init.h>
#include <linux/irqflags.h>
#include <linux/jump_label.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of_device.h>
#include <linux/of.h>
#include <linux/of_irq.h>
#include <linux/pm_domain.h>
#include <linux/pm_runtime.h>
#include <linux/pm_wakeirq.h>
#include <linux/property.h>
#include <linux/rwsem.h>
#include <linux/slab.h>

#include "i2c-core.h"

#define CREATE_TRACE_POINTS
#include <trace/events/i2c.h>

#define I2C_ADDR_OFFSET_TEN_BIT 0xa000
#define I2C_ADDR_OFFSET_SLAVE   0x1000

#define I2C_ADDR_7BITS_MAX      0x77
#define I2C_ADDR_7BITS_COUNT    (I2C_ADDR_7BITS_MAX + 1)

#define I2C_ADDR_DEVICE_ID      0x7c

/*
 * core_lock protects i2c_adapter_idr, and guarantees that device detection,
 * deletion of detected devices are serialized
 */
static DEFINE_MUTEX(core_lock);
static DEFINE_IDR(i2c_adapter_idr);

static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);

static DEFINE_STATIC_KEY_FALSE(i2c_trace_msg_key);
static bool is_registered;

int i2c_transfer_trace_reg(void)
{
        static_branch_inc(&i2c_trace_msg_key);
        return 0;
}

void i2c_transfer_trace_unreg(void)
{
        static_branch_dec(&i2c_trace_msg_key);
}

const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,
                                                const struct i2c_client *client)
{
        if (!(id && client))
                return NULL;

        while (id->name[0]) {
                if (strcmp(client->name, id->name) == 0)
                        return id;
                id++;
        }
        return NULL;
}
EXPORT_SYMBOL_GPL(i2c_match_id);

static int i2c_device_match(struct device *dev, struct device_driver *drv)
{
        struct i2c_client       *client = i2c_verify_client(dev);
        struct i2c_driver       *driver;


        /* Attempt an OF style match */
        if (i2c_of_match_device(drv->of_match_table, client))
                return 1;

        /* Then ACPI style match */
        if (acpi_driver_match_device(dev, drv))
                return 1;

        driver = to_i2c_driver(drv);

        /* Finally an I2C match */
        if (i2c_match_id(driver->id_table, client))
                return 1;

        return 0;
}

static int i2c_device_uevent(struct device *dev, struct kobj_uevent_env *env)
{
        struct i2c_client *client = to_i2c_client(dev);
        int rc;

        rc = of_device_uevent_modalias(dev, env);
        if (rc != -ENODEV)
                return rc;

        rc = acpi_device_uevent_modalias(dev, env);
        if (rc != -ENODEV)
                return rc;

        return add_uevent_var(env, "MODALIAS=%s%s", I2C_MODULE_PREFIX, client->name);
}

/* i2c bus recovery routines */
static int get_scl_gpio_value(struct i2c_adapter *adap)
{
        return gpiod_get_value_cansleep(adap->bus_recovery_info->scl_gpiod);
}

static void set_scl_gpio_value(struct i2c_adapter *adap, int val)
{
        gpiod_set_value_cansleep(adap->bus_recovery_info->scl_gpiod, val);
}

static int get_sda_gpio_value(struct i2c_adapter *adap)
{
        return gpiod_get_value_cansleep(adap->bus_recovery_info->sda_gpiod);
}

static void set_sda_gpio_value(struct i2c_adapter *adap, int val)
{
        gpiod_set_value_cansleep(adap->bus_recovery_info->sda_gpiod, val);
}

static int i2c_generic_bus_free(struct i2c_adapter *adap)
{
        struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
        int ret = -EOPNOTSUPP;

        if (bri->get_bus_free)
                ret = bri->get_bus_free(adap);
        else if (bri->get_sda)
                ret = bri->get_sda(adap);

        if (ret < 0)
                return ret;

        return ret ? 0 : -EBUSY;
}

/*
 * We are generating clock pulses. ndelay() determines durating of clk pulses.
 * We will generate clock with rate 100 KHz and so duration of both clock levels
 * is: delay in ns = (10^6 / 100) / 2
 */
#define RECOVERY_NDELAY         5000
#define RECOVERY_CLK_CNT        9

int i2c_generic_scl_recovery(struct i2c_adapter *adap)
{
        struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
        int i = 0, scl = 1, ret = 0;

        if (bri->prepare_recovery)
                bri->prepare_recovery(adap);

        /*
         * If we can set SDA, we will always create a STOP to ensure additional
         * pulses will do no harm. This is achieved by letting SDA follow SCL
         * half a cycle later. Check the 'incomplete_write_byte' fault injector
         * for details. Note that we must honour tsu:sto, 4us, but lets use 5us
         * here for simplicity.
         */
        bri->set_scl(adap, scl);
        ndelay(RECOVERY_NDELAY);
        if (bri->set_sda)
                bri->set_sda(adap, scl);
        ndelay(RECOVERY_NDELAY / 2);

        /*
         * By this time SCL is high, as we need to give 9 falling-rising edges
         */
        while (i++ < RECOVERY_CLK_CNT * 2) {
                if (scl) {
                        /* SCL shouldn't be low here */
                        if (!bri->get_scl(adap)) {
                                dev_err(&adap->dev,
                                        "SCL is stuck low, exit recovery\n");
                                ret = -EBUSY;
                                break;
                        }
                }

                scl = !scl;
                bri->set_scl(adap, scl);
                /* Creating STOP again, see above */
                if (scl)  {
                        /* Honour minimum tsu:sto */
                        ndelay(RECOVERY_NDELAY);
                } else {
                        /* Honour minimum tf and thd:dat */
                        ndelay(RECOVERY_NDELAY / 2);
                }
                if (bri->set_sda)
                        bri->set_sda(adap, scl);
                ndelay(RECOVERY_NDELAY / 2);

                if (scl) {
                        ret = i2c_generic_bus_free(adap);
                        if (ret == 0)
                                break;
                }
        }

        /* If we can't check bus status, assume recovery worked */
        if (ret == -EOPNOTSUPP)
                ret = 0;

        if (bri->unprepare_recovery)
                bri->unprepare_recovery(adap);

        return ret;
}
EXPORT_SYMBOL_GPL(i2c_generic_scl_recovery);

int i2c_recover_bus(struct i2c_adapter *adap)
{
        if (!adap->bus_recovery_info)
                return -EOPNOTSUPP;

        dev_dbg(&adap->dev, "Trying i2c bus recovery\n");
        return adap->bus_recovery_info->recover_bus(adap);
}
EXPORT_SYMBOL_GPL(i2c_recover_bus);

static void i2c_init_recovery(struct i2c_adapter *adap)
{
        struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
        char *err_str;

        if (!bri)
                return;

        if (!bri->recover_bus) {
                err_str = "no recover_bus() found";
                goto err;
        }

        if (bri->scl_gpiod && bri->recover_bus == i2c_generic_scl_recovery) {
                bri->get_scl = get_scl_gpio_value;
                bri->set_scl = set_scl_gpio_value;
                if (bri->sda_gpiod) {
                        bri->get_sda = get_sda_gpio_value;
                        /* FIXME: add proper flag instead of '0' once available */
                        if (gpiod_get_direction(bri->sda_gpiod) == 0)
                                bri->set_sda = set_sda_gpio_value;
                }
                return;
        }

        if (bri->recover_bus == i2c_generic_scl_recovery) {
                /* Generic SCL recovery */
                if (!bri->set_scl || !bri->get_scl) {
                        err_str = "no {get|set}_scl() found";
                        goto err;
                }
                if (!bri->set_sda && !bri->get_sda) {
                        err_str = "either get_sda() or set_sda() needed";
                        goto err;
                }
        }

        return;
 err:
        dev_err(&adap->dev, "Not using recovery: %s\n", err_str);
        adap->bus_recovery_info = NULL;
}

static int i2c_smbus_host_notify_to_irq(const struct i2c_client *client)
{
        struct i2c_adapter *adap = client->adapter;
        unsigned int irq;

        if (!adap->host_notify_domain)
                return -ENXIO;

        if (client->flags & I2C_CLIENT_TEN)
                return -EINVAL;

        irq = irq_create_mapping(adap->host_notify_domain, client->addr);

        return irq > 0 ? irq : -ENXIO;
}

static int i2c_device_probe(struct device *dev)
{
        struct i2c_client       *client = i2c_verify_client(dev);
        struct i2c_driver       *driver;
        int status;

        if (!client)
                return 0;

        driver = to_i2c_driver(dev->driver);

        if (!client->irq && !driver->disable_i2c_core_irq_mapping) {
                int irq = -ENOENT;

                if (client->flags & I2C_CLIENT_HOST_NOTIFY) {
                        dev_dbg(dev, "Using Host Notify IRQ\n");
                        /* Keep adapter active when Host Notify is required */
                        pm_runtime_get_sync(&client->adapter->dev);
                        irq = i2c_smbus_host_notify_to_irq(client);
                } else if (dev->of_node) {
                        irq = of_irq_get_byname(dev->of_node, "irq");
                        if (irq == -EINVAL || irq == -ENODATA)
                                irq = of_irq_get(dev->of_node, 0);
                } else if (ACPI_COMPANION(dev)) {
                        irq = acpi_dev_gpio_irq_get(ACPI_COMPANION(dev), 0);
                }
                if (irq == -EPROBE_DEFER)
                        return irq;

                if (irq < 0)
                        irq = 0;

                client->irq = irq;
        }

        /*
         * An I2C ID table is not mandatory, if and only if, a suitable OF
         * or ACPI ID table is supplied for the probing device.
         */
        if (!driver->id_table &&
            !i2c_acpi_match_device(dev->driver->acpi_match_table, client) &&
            !i2c_of_match_device(dev->driver->of_match_table, client))
                return -ENODEV;

        if (client->flags & I2C_CLIENT_WAKE) {
                int wakeirq = -ENOENT;

                if (dev->of_node) {
                        wakeirq = of_irq_get_byname(dev->of_node, "wakeup");
                        if (wakeirq == -EPROBE_DEFER)
                                return wakeirq;
                }

                device_init_wakeup(&client->dev, true);

                if (wakeirq > 0 && wakeirq != client->irq)
                        status = dev_pm_set_dedicated_wake_irq(dev, wakeirq);
                else if (client->irq > 0)
                        status = dev_pm_set_wake_irq(dev, client->irq);
                else
                        status = 0;

                if (status)
                        dev_warn(&client->dev, "failed to set up wakeup irq\n");
        }

        dev_dbg(dev, "probe\n");

        status = of_clk_set_defaults(dev->of_node, false);
        if (status < 0)
                goto err_clear_wakeup_irq;

        status = dev_pm_domain_attach(&client->dev, true);
        if (status)
                goto err_clear_wakeup_irq;

        /*
         * When there are no more users of probe(),
         * rename probe_new to probe.
         */
        if (driver->probe_new)
                status = driver->probe_new(client);
        else if (driver->probe)
                status = driver->probe(client,
                                       i2c_match_id(driver->id_table, client));
        else
                status = -EINVAL;

        if (status)
                goto err_detach_pm_domain;

        return 0;

err_detach_pm_domain:
        dev_pm_domain_detach(&client->dev, true);
err_clear_wakeup_irq:
        dev_pm_clear_wake_irq(&client->dev);
        device_init_wakeup(&client->dev, false);
        return status;
}

static int i2c_device_remove(struct device *dev)
{
        struct i2c_client       *client = i2c_verify_client(dev);
        struct i2c_driver       *driver;
        int status = 0;

        if (!client || !dev->driver)
                return 0;

        driver = to_i2c_driver(dev->driver);
        if (driver->remove) {
                dev_dbg(dev, "remove\n");
                status = driver->remove(client);
        }

        dev_pm_domain_detach(&client->dev, true);

        dev_pm_clear_wake_irq(&client->dev);
        device_init_wakeup(&client->dev, false);

        client->irq = client->init_irq;
        if (client->flags & I2C_CLIENT_HOST_NOTIFY)
                pm_runtime_put(&client->adapter->dev);

        return status;
}

static void i2c_device_shutdown(struct device *dev)
{
        struct i2c_client *client = i2c_verify_client(dev);
        struct i2c_driver *driver;

        if (!client || !dev->driver)
                return;
        driver = to_i2c_driver(dev->driver);
        if (driver->shutdown)
                driver->shutdown(client);
}

static void i2c_client_dev_release(struct device *dev)
{
        kfree(to_i2c_client(dev));
}

static ssize_t
show_name(struct device *dev, struct device_attribute *attr, char *buf)
{
        return sprintf(buf, "%s\n", dev->type == &i2c_client_type ?
                       to_i2c_client(dev)->name : to_i2c_adapter(dev)->name);
}
static DEVICE_ATTR(name, S_IRUGO, show_name, NULL);

static ssize_t
show_modalias(struct device *dev, struct device_attribute *attr, char *buf)
{
        struct i2c_client *client = to_i2c_client(dev);
        int len;

        len = of_device_modalias(dev, buf, PAGE_SIZE);
        if (len != -ENODEV)
                return len;

        len = acpi_device_modalias(dev, buf, PAGE_SIZE -1);
        if (len != -ENODEV)
                return len;

        return sprintf(buf, "%s%s\n", I2C_MODULE_PREFIX, client->name);
}
static DEVICE_ATTR(modalias, S_IRUGO, show_modalias, NULL);

static struct attribute *i2c_dev_attrs[] = {
        &dev_attr_name.attr,
        /* modalias helps coldplug:  modprobe $(cat .../modalias) */
        &dev_attr_modalias.attr,
        NULL
};
ATTRIBUTE_GROUPS(i2c_dev);

struct bus_type i2c_bus_type = {
        .name           = "i2c",
        .match          = i2c_device_match,
        .probe          = i2c_device_probe,
        .remove         = i2c_device_remove,
        .shutdown       = i2c_device_shutdown,
};
EXPORT_SYMBOL_GPL(i2c_bus_type);

struct device_type i2c_client_type = {
        .groups         = i2c_dev_groups,
        .uevent         = i2c_device_uevent,
        .release        = i2c_client_dev_release,
};
EXPORT_SYMBOL_GPL(i2c_client_type);


/**
 * i2c_verify_client - return parameter as i2c_client, or NULL
 * @dev: device, probably from some driver model iterator
 *
 * When traversing the driver model tree, perhaps using driver model
 * iterators like @device_for_each_child(), you can't assume very much
 * about the nodes you find.  Use this function to avoid oopses caused
 * by wrongly treating some non-I2C device as an i2c_client.
 */
struct i2c_client *i2c_verify_client(struct device *dev)
{
        return (dev->type == &i2c_client_type)
                        ? to_i2c_client(dev)
                        : NULL;
}
EXPORT_SYMBOL(i2c_verify_client);


/* Return a unique address which takes the flags of the client into account */
static unsigned short i2c_encode_flags_to_addr(struct i2c_client *client)
{
        unsigned short addr = client->addr;

        /* For some client flags, add an arbitrary offset to avoid collisions */
        if (client->flags & I2C_CLIENT_TEN)
                addr |= I2C_ADDR_OFFSET_TEN_BIT;

        if (client->flags & I2C_CLIENT_SLAVE)
                addr |= I2C_ADDR_OFFSET_SLAVE;

        return addr;
}

/* This is a permissive address validity check, I2C address map constraints
 * are purposely not enforced, except for the general call address. */
static int i2c_check_addr_validity(unsigned int addr, unsigned short flags)
{
        if (flags & I2C_CLIENT_TEN) {
                /* 10-bit address, all values are valid */
                if (addr > 0x3ff)
                        return -EINVAL;
        } else {
                /* 7-bit address, reject the general call address */
                if (addr == 0x00 || addr > 0x7f)
                        return -EINVAL;
        }
        return 0;
}

/* And this is a strict address validity check, used when probing. If a
 * device uses a reserved address, then it shouldn't be probed. 7-bit
 * addressing is assumed, 10-bit address devices are rare and should be
 * explicitly enumerated. */
int i2c_check_7bit_addr_validity_strict(unsigned short addr)
{
        /*
         * Reserved addresses per I2C specification:
         *  0x00       General call address / START byte
         *  0x01       CBUS address
         *  0x02       Reserved for different bus format
         *  0x03       Reserved for future purposes
         *  0x04-0x07  Hs-mode master code
         *  0x78-0x7b  10-bit slave addressing
         *  0x7c-0x7f  Reserved for future purposes
         */
        if (addr < 0x08 || addr > 0x77)
                return -EINVAL;
        return 0;
}

static int __i2c_check_addr_busy(struct device *dev, void *addrp)
{
        struct i2c_client       *client = i2c_verify_client(dev);
        int                     addr = *(int *)addrp;

        if (client && i2c_encode_flags_to_addr(client) == addr)
                return -EBUSY;
        return 0;
}

/* walk up mux tree */
static int i2c_check_mux_parents(struct i2c_adapter *adapter, int addr)
{
        struct i2c_adapter *parent = i2c_parent_is_i2c_adapter(adapter);
        int result;

        result = device_for_each_child(&adapter->dev, &addr,
                                        __i2c_check_addr_busy);

        if (!result && parent)
                result = i2c_check_mux_parents(parent, addr);

        return result;
}

/* recurse down mux tree */
static int i2c_check_mux_children(struct device *dev, void *addrp)
{
        int result;

        if (dev->type == &i2c_adapter_type)
                result = device_for_each_child(dev, addrp,
                                                i2c_check_mux_children);
        else
                result = __i2c_check_addr_busy(dev, addrp);

        return result;
}

static int i2c_check_addr_busy(struct i2c_adapter *adapter, int addr)
{
        struct i2c_adapter *parent = i2c_parent_is_i2c_adapter(adapter);
        int result = 0;

        if (parent)
                result = i2c_check_mux_parents(parent, addr);

        if (!result)
                result = device_for_each_child(&adapter->dev, &addr,
                                                i2c_check_mux_children);

        return result;
}

/**
 * i2c_adapter_lock_bus - Get exclusive access to an I2C bus segment
 * @adapter: Target I2C bus segment
 * @flags: I2C_LOCK_ROOT_ADAPTER locks the root i2c adapter, I2C_LOCK_SEGMENT
 *      locks only this branch in the adapter tree
 */
static void i2c_adapter_lock_bus(struct i2c_adapter *adapter,
                                 unsigned int flags)
{
        rt_mutex_lock_nested(&adapter->bus_lock, i2c_adapter_depth(adapter));
}

/**
 * i2c_adapter_trylock_bus - Try to get exclusive access to an I2C bus segment
 * @adapter: Target I2C bus segment
 * @flags: I2C_LOCK_ROOT_ADAPTER trylocks the root i2c adapter, I2C_LOCK_SEGMENT
 *      trylocks only this branch in the adapter tree
 */
static int i2c_adapter_trylock_bus(struct i2c_adapter *adapter,
                                   unsigned int flags)
{
        return rt_mutex_trylock(&adapter->bus_lock);
}

/**
 * i2c_adapter_unlock_bus - Release exclusive access to an I2C bus segment
 * @adapter: Target I2C bus segment
 * @flags: I2C_LOCK_ROOT_ADAPTER unlocks the root i2c adapter, I2C_LOCK_SEGMENT
 *      unlocks only this branch in the adapter tree
 */
static void i2c_adapter_unlock_bus(struct i2c_adapter *adapter,
                                   unsigned int flags)
{
        rt_mutex_unlock(&adapter->bus_lock);
}

static void i2c_dev_set_name(struct i2c_adapter *adap,
                             struct i2c_client *client,
                             struct i2c_board_info const *info)
{
        struct acpi_device *adev = ACPI_COMPANION(&client->dev);

        if (info && info->dev_name) {
                dev_set_name(&client->dev, "i2c-%s", info->dev_name);
                return;
        }

        if (adev) {
                dev_set_name(&client->dev, "i2c-%s", acpi_dev_name(adev));
                return;
        }

        dev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap),
                     i2c_encode_flags_to_addr(client));
}

static int i2c_dev_irq_from_resources(const struct resource *resources,
                                      unsigned int num_resources)
{
        struct irq_data *irqd;
        int i;

        for (i = 0; i < num_resources; i++) {
                const struct resource *r = &resources[i];

                if (resource_type(r) != IORESOURCE_IRQ)
                        continue;

                if (r->flags & IORESOURCE_BITS) {
                        irqd = irq_get_irq_data(r->start);
                        if (!irqd)
                                break;

                        irqd_set_trigger_type(irqd, r->flags & IORESOURCE_BITS);
                }

                return r->start;
        }

        return 0;
}

/**
 * i2c_new_device - instantiate an i2c device
 * @adap: the adapter managing the device
 * @info: describes one I2C device; bus_num is ignored
 * Context: can sleep
 *
 * Create an i2c device. Binding is handled through driver model
 * probe()/remove() methods.  A driver may be bound to this device when we
 * return from this function, or any later moment (e.g. maybe hotplugging will
 * load the driver module).  This call is not appropriate for use by mainboard
 * initialization logic, which usually runs during an arch_initcall() long
 * before any i2c_adapter could exist.
 *
 * This returns the new i2c client, which may be saved for later use with
 * i2c_unregister_device(); or NULL to indicate an error.
 */
struct i2c_client *
i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info)
{
        struct i2c_client       *client;
        int                     status;

        client = kzalloc(sizeof *client, GFP_KERNEL);
        if (!client)
                return NULL;

        client->adapter = adap;

        client->dev.platform_data = info->platform_data;
        client->flags = info->flags;
        client->addr = info->addr;

        client->init_irq = info->irq;
        if (!client->init_irq)
                client->init_irq = i2c_dev_irq_from_resources(info->resources,
                                                         info->num_resources);
        client->irq = client->init_irq;

        strlcpy(client->name, info->type, sizeof(client->name));

        status = i2c_check_addr_validity(client->addr, client->flags);
        if (status) {
                dev_err(&adap->dev, "Invalid %d-bit I2C address 0x%02hx\n",
                        client->flags & I2C_CLIENT_TEN ? 10 : 7, client->addr);
                goto out_err_silent;
        }

        /* Check for address business */
        status = i2c_check_addr_busy(adap, i2c_encode_flags_to_addr(client));
        if (status)
                goto out_err;

        client->dev.parent = &client->adapter->dev;
        client->dev.bus = &i2c_bus_type;
        client->dev.type = &i2c_client_type;
        client->dev.of_node = of_node_get(info->of_node);
        client->dev.fwnode = info->fwnode;

        i2c_dev_set_name(adap, client, info);

        if (info->properties) {
                status = device_add_properties(&client->dev, info->properties);
                if (status) {
                        dev_err(&adap->dev,
                                "Failed to add properties to client %s: %d\n",
                                client->name, status);
                        goto out_err_put_of_node;
                }
        }

        status = device_register(&client->dev);
        if (status)
                goto out_free_props;

        dev_dbg(&adap->dev, "client [%s] registered with bus id %s\n",
                client->name, dev_name(&client->dev));

        return client;

out_free_props:
        if (info->properties)
                device_remove_properties(&client->dev);
out_err_put_of_node:
        of_node_put(info->of_node);
out_err:
        dev_err(&adap->dev,
                "Failed to register i2c client %s at 0x%02x (%d)\n",
                client->name, client->addr, status);
out_err_silent:
        kfree(client);
        return NULL;
}
EXPORT_SYMBOL_GPL(i2c_new_device);


/**
 * i2c_unregister_device - reverse effect of i2c_new_device()
 * @client: value returned from i2c_new_device()
 * Context: can sleep
 */
void i2c_unregister_device(struct i2c_client *client)
{
        if (!client)
                return;

        if (client->dev.of_node) {
                of_node_clear_flag(client->dev.of_node, OF_POPULATED);
                of_node_put(client->dev.of_node);
        }

        if (ACPI_COMPANION(&client->dev))
                acpi_device_clear_enumerated(ACPI_COMPANION(&client->dev));
        device_unregister(&client->dev);
}
EXPORT_SYMBOL_GPL(i2c_unregister_device);


static const struct i2c_device_id dummy_id[] = {
        { "dummy", 0 },
        { },
};

static int dummy_probe(struct i2c_client *client,
                       const struct i2c_device_id *id)
{
        return 0;
}

static int dummy_remove(struct i2c_client *client)
{
        return 0;
}

static struct i2c_driver dummy_driver = {
        .driver.name    = "dummy",
        .probe          = dummy_probe,
        .remove         = dummy_remove,
        .id_table       = dummy_id,
};

/**
 * i2c_new_dummy - return a new i2c device bound to a dummy driver
 * @adapter: the adapter managing the device
 * @address: seven bit address to be used
 * Context: can sleep
 *
 * This returns an I2C client bound to the "dummy" driver, intended for use
 * with devices that consume multiple addresses.  Examples of such chips
 * include various EEPROMS (like 24c04 and 24c08 models).
 *
 * These dummy devices have two main uses.  First, most I2C and SMBus calls
 * except i2c_transfer() need a client handle; the dummy will be that handle.
 * And second, this prevents the specified address from being bound to a
 * different driver.
 *
 * This returns the new i2c client, which should be saved for later use with
 * i2c_unregister_device(); or NULL to indicate an error.
 */
struct i2c_client *i2c_new_dummy(struct i2c_adapter *adapter, u16 address)
{
        struct i2c_board_info info = {
                I2C_BOARD_INFO("dummy", address),
        };

        return i2c_new_device(adapter, &info);
}
EXPORT_SYMBOL_GPL(i2c_new_dummy);

/**
 * i2c_new_secondary_device - Helper to get the instantiated secondary address
 * and create the associated device
 * @client: Handle to the primary client
 * @name: Handle to specify which secondary address to get
 * @default_addr: Used as a fallback if no secondary address was specified
 * Context: can sleep
 *
 * I2C clients can be composed of multiple I2C slaves bound together in a single
 * component. The I2C client driver then binds to the master I2C slave and needs
 * to create I2C dummy clients to communicate with all the other slaves.
 *
 * This function creates and returns an I2C dummy client whose I2C address is
 * retrieved from the platform firmware based on the given slave name. If no
 * address is specified by the firmware default_addr is used.
 *
 * On DT-based platforms the address is retrieved from the "reg" property entry
 * cell whose "reg-names" value matches the slave name.
 *
 * This returns the new i2c client, which should be saved for later use with
 * i2c_unregister_device(); or NULL to indicate an error.
 */
struct i2c_client *i2c_new_secondary_device(struct i2c_client *client,
                                                const char *name,
                                                u16 default_addr)
{
        struct device_node *np = client->dev.of_node;
        u32 addr = default_addr;
        int i;

        if (np) {
                i = of_property_match_string(np, "reg-names", name);
                if (i >= 0)
                        of_property_read_u32_index(np, "reg", i, &addr);
        }

        dev_dbg(&client->adapter->dev, "Address for %s : 0x%x\n", name, addr);
        return i2c_new_dummy(client->adapter, addr);
}
EXPORT_SYMBOL_GPL(i2c_new_secondary_device);

/* ------------------------------------------------------------------------- */

/* I2C bus adapters -- one roots each I2C or SMBUS segment */

static void i2c_adapter_dev_release(struct device *dev)
{
        struct i2c_adapter *adap = to_i2c_adapter(dev);
        complete(&adap->dev_released);
}

unsigned int i2c_adapter_depth(struct i2c_adapter *adapter)
{
        unsigned int depth = 0;

        while ((adapter = i2c_parent_is_i2c_adapter(adapter)))
                depth++;

        WARN_ONCE(depth >= MAX_LOCKDEP_SUBCLASSES,
                  "adapter depth exceeds lockdep subclass limit\n");

        return depth;
}
EXPORT_SYMBOL_GPL(i2c_adapter_depth);

/*
 * Let users instantiate I2C devices through sysfs. This can be used when
 * platform initialization code doesn't contain the proper data for
 * whatever reason. Also useful for drivers that do device detection and
 * detection fails, either because the device uses an unexpected address,
 * or this is a compatible device with different ID register values.
 *
 * Parameter checking may look overzealous, but we really don't want
 * the user to provide incorrect parameters.
 */
static ssize_t
i2c_sysfs_new_device(struct device *dev, struct device_attribute *attr,
                     const char *buf, size_t count)
{
        struct i2c_adapter *adap = to_i2c_adapter(dev);
        struct i2c_board_info info;
        struct i2c_client *client;
        char *blank, end;
        int res;

        memset(&info, 0, sizeof(struct i2c_board_info));

        blank = strchr(buf, ' ');
        if (!blank) {
                dev_err(dev, "%s: Missing parameters\n", "new_device");
                return -EINVAL;
        }
        if (blank - buf > I2C_NAME_SIZE - 1) {
                dev_err(dev, "%s: Invalid device name\n", "new_device");
                return -EINVAL;
        }
        memcpy(info.type, buf, blank - buf);

        /* Parse remaining parameters, reject extra parameters */
        res = sscanf(++blank, "%hi%c", &info.addr, &end);
        if (res < 1) {
                dev_err(dev, "%s: Can't parse I2C address\n", "new_device");
                return -EINVAL;
        }
        if (res > 1  && end != '\n') {
                dev_err(dev, "%s: Extra parameters\n", "new_device");
                return -EINVAL;
        }

        if ((info.addr & I2C_ADDR_OFFSET_TEN_BIT) == I2C_ADDR_OFFSET_TEN_BIT) {
                info.addr &= ~I2C_ADDR_OFFSET_TEN_BIT;
                info.flags |= I2C_CLIENT_TEN;
        }

        if (info.addr & I2C_ADDR_OFFSET_SLAVE) {
                info.addr &= ~I2C_ADDR_OFFSET_SLAVE;
                info.flags |= I2C_CLIENT_SLAVE;
        }

        client = i2c_new_device(adap, &info);
        if (!client)
                return -EINVAL;

        /* Keep track of the added device */
        mutex_lock(&adap->userspace_clients_lock);
        list_add_tail(&client->detected, &adap->userspace_clients);
        mutex_unlock(&adap->userspace_clients_lock);
        dev_info(dev, "%s: Instantiated device %s at 0x%02hx\n", "new_device",
                 info.type, info.addr);

        return count;
}
static DEVICE_ATTR(new_device, S_IWUSR, NULL, i2c_sysfs_new_device);

/*
 * And of course let the users delete the devices they instantiated, if
 * they got it wrong. This interface can only be used to delete devices
 * instantiated by i2c_sysfs_new_device above. This guarantees that we
 * don't delete devices to which some kernel code still has references.
 *
 * Parameter checking may look overzealous, but we really don't want
 * the user to delete the wrong device.
 */
static ssize_t
i2c_sysfs_delete_device(struct device *dev, struct device_attribute *attr,
                        const char *buf, size_t count)
{
        struct i2c_adapter *adap = to_i2c_adapter(dev);
        struct i2c_client *client, *next;
        unsigned short addr;
        char end;
        int res;

        /* Parse parameters, reject extra parameters */
        res = sscanf(buf, "%hi%c", &addr, &end);
        if (res < 1) {
                dev_err(dev, "%s: Can't parse I2C address\n", "delete_device");
                return -EINVAL;
        }
        if (res > 1  && end != '\n') {
                dev_err(dev, "%s: Extra parameters\n", "delete_device");
                return -EINVAL;
        }

        /* Make sure the device was added through sysfs */
        res = -ENOENT;
        mutex_lock_nested(&adap->userspace_clients_lock,
                          i2c_adapter_depth(adap));
        list_for_each_entry_safe(client, next, &adap->userspace_clients,
                                 detected) {
                if (i2c_encode_flags_to_addr(client) == addr) {
                        dev_info(dev, "%s: Deleting device %s at 0x%02hx\n",
                                 "delete_device", client->name, client->addr);

                        list_del(&client->detected);
                        i2c_unregister_device(client);
                        res = count;
                        break;
                }
        }
        mutex_unlock(&adap->userspace_clients_lock);

        if (res < 0)
                dev_err(dev, "%s: Can't find device in list\n",
                        "delete_device");
        return res;
}
static DEVICE_ATTR_IGNORE_LOCKDEP(delete_device, S_IWUSR, NULL,
                                   i2c_sysfs_delete_device);

static struct attribute *i2c_adapter_attrs[] = {
        &dev_attr_name.attr,
        &dev_attr_new_device.attr,
        &dev_attr_delete_device.attr,
        NULL
};
ATTRIBUTE_GROUPS(i2c_adapter);

struct device_type i2c_adapter_type = {
        .groups         = i2c_adapter_groups,
        .release        = i2c_adapter_dev_release,
};
EXPORT_SYMBOL_GPL(i2c_adapter_type);

/**
 * i2c_verify_adapter - return parameter as i2c_adapter or NULL
 * @dev: device, probably from some driver model iterator
 *
 * When traversing the driver model tree, perhaps using driver model
 * iterators like @device_for_each_child(), you can't assume very much
 * about the nodes you find.  Use this function to avoid oopses caused
 * by wrongly treating some non-I2C device as an i2c_adapter.
 */
struct i2c_adapter *i2c_verify_adapter(struct device *dev)
{
        return (dev->type == &i2c_adapter_type)
                        ? to_i2c_adapter(dev)
                        : NULL;
}
EXPORT_SYMBOL(i2c_verify_adapter);

#ifdef CONFIG_I2C_COMPAT
static struct class_compat *i2c_adapter_compat_class;
#endif

static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
{
        struct i2c_devinfo      *devinfo;

        down_read(&__i2c_board_lock);
        list_for_each_entry(devinfo, &__i2c_board_list, list) {
                if (devinfo->busnum == adapter->nr
                                && !i2c_new_device(adapter,
                                                &devinfo->board_info))
                        dev_err(&adapter->dev,
                                "Can't create device at 0x%02x\n",
                                devinfo->board_info.addr);
        }
        up_read(&__i2c_board_lock);
}

static int i2c_do_add_adapter(struct i2c_driver *driver,
                              struct i2c_adapter *adap)
{
        /* Detect supported devices on that bus, and instantiate them */
        i2c_detect(adap, driver);

        return 0;
}

static int __process_new_adapter(struct device_driver *d, void *data)
{
        return i2c_do_add_adapter(to_i2c_driver(d), data);
}

static const struct i2c_lock_operations i2c_adapter_lock_ops = {
        .lock_bus =    i2c_adapter_lock_bus,
        .trylock_bus = i2c_adapter_trylock_bus,
        .unlock_bus =  i2c_adapter_unlock_bus,
};

static void i2c_host_notify_irq_teardown(struct i2c_adapter *adap)
{
        struct irq_domain *domain = adap->host_notify_domain;
        irq_hw_number_t hwirq;

        if (!domain)
                return;

        for (hwirq = 0 ; hwirq < I2C_ADDR_7BITS_COUNT ; hwirq++)
                irq_dispose_mapping(irq_find_mapping(domain, hwirq));

        irq_domain_remove(domain);
        adap->host_notify_domain = NULL;
}

static int i2c_host_notify_irq_map(struct irq_domain *h,
                                          unsigned int virq,
                                          irq_hw_number_t hw_irq_num)
{
        irq_set_chip_and_handler(virq, &dummy_irq_chip, handle_simple_irq);

        return 0;
}

static const struct irq_domain_ops i2c_host_notify_irq_ops = {
        .map = i2c_host_notify_irq_map,
};

static int i2c_setup_host_notify_irq_domain(struct i2c_adapter *adap)
{
        struct irq_domain *domain;

        if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_HOST_NOTIFY))
                return 0;

        domain = irq_domain_create_linear(adap->dev.fwnode,
                                          I2C_ADDR_7BITS_COUNT,
                                          &i2c_host_notify_irq_ops, adap);
        if (!domain)
                return -ENOMEM;

        adap->host_notify_domain = domain;

        return 0;
}

/**
 * i2c_handle_smbus_host_notify - Forward a Host Notify event to the correct
 * I2C client.
 * @adap: the adapter
 * @addr: the I2C address of the notifying device
 * Context: can't sleep
 *
 * Helper function to be called from an I2C bus driver's interrupt
 * handler. It will schedule the Host Notify IRQ.
 */
int i2c_handle_smbus_host_notify(struct i2c_adapter *adap, unsigned short addr)
{
        int irq;

        if (!adap)
                return -EINVAL;

        irq = irq_find_mapping(adap->host_notify_domain, addr);
        if (irq <= 0)
                return -ENXIO;

        generic_handle_irq(irq);

        return 0;
}
EXPORT_SYMBOL_GPL(i2c_handle_smbus_host_notify);

static int i2c_register_adapter(struct i2c_adapter *adap)
{
        int res = -EINVAL;

        /* Can't register until after driver model init */
        if (WARN_ON(!is_registered)) {
                res = -EAGAIN;
                goto out_list;
        }

        /* Sanity checks */
        if (WARN(!adap->name[0], "i2c adapter has no name"))
                goto out_list;

        if (!adap->algo) {
                pr_err("adapter '%s': no algo supplied!\n", adap->name);
                goto out_list;
        }

        if (!adap->lock_ops)
                adap->lock_ops = &i2c_adapter_lock_ops;

        rt_mutex_init(&adap->bus_lock);
        rt_mutex_init(&adap->mux_lock);
        mutex_init(&adap->userspace_clients_lock);
        INIT_LIST_HEAD(&adap->userspace_clients);

        /* Set default timeout to 1 second if not already set */
        if (adap->timeout == 0)
                adap->timeout = HZ;

        /* register soft irqs for Host Notify */
        res = i2c_setup_host_notify_irq_domain(adap);
        if (res) {
                pr_err("adapter '%s': can't create Host Notify IRQs (%d)\n",
                       adap->name, res);
                goto out_list;
        }

        dev_set_name(&adap->dev, "i2c-%d", adap->nr);
        adap->dev.bus = &i2c_bus_type;
        adap->dev.type = &i2c_adapter_type;
        res = device_register(&adap->dev);
        if (res) {
                pr_err("adapter '%s': can't register device (%d)\n", adap->name, res);
                goto out_list;
        }

        res = of_i2c_setup_smbus_alert(adap);
        if (res)
                goto out_reg;

        dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);

        pm_runtime_no_callbacks(&adap->dev);
        pm_suspend_ignore_children(&adap->dev, true);
        pm_runtime_enable(&adap->dev);

#ifdef CONFIG_I2C_COMPAT
        res = class_compat_create_link(i2c_adapter_compat_class, &adap->dev,
                                       adap->dev.parent);
        if (res)
                dev_warn(&adap->dev,
                         "Failed to create compatibility class link\n");
#endif

        i2c_init_recovery(adap);

        /* create pre-declared device nodes */
        of_i2c_register_devices(adap);
        i2c_acpi_register_devices(adap);
        i2c_acpi_install_space_handler(adap);

        if (adap->nr < __i2c_first_dynamic_bus_num)
                i2c_scan_static_board_info(adap);

        /* Notify drivers */
        mutex_lock(&core_lock);
        bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
        mutex_unlock(&core_lock);

        return 0;

out_reg:
        init_completion(&adap->dev_released);
        device_unregister(&adap->dev);
        wait_for_completion(&adap->dev_released);
out_list:
        mutex_lock(&core_lock);
        idr_remove(&i2c_adapter_idr, adap->nr);
        mutex_unlock(&core_lock);
        return res;
}

/**
 * __i2c_add_numbered_adapter - i2c_add_numbered_adapter where nr is never -1
 * @adap: the adapter to register (with adap->nr initialized)
 * Context: can sleep
 *
 * See i2c_add_numbered_adapter() for details.
 */
static int __i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
        int id;

        mutex_lock(&core_lock);
        id = idr_alloc(&i2c_adapter_idr, adap, adap->nr, adap->nr + 1, GFP_KERNEL);
        mutex_unlock(&core_lock);
        if (WARN(id < 0, "couldn't get idr"))
                return id == -ENOSPC ? -EBUSY : id;

        return i2c_register_adapter(adap);
}

/**
 * i2c_add_adapter - declare i2c adapter, use dynamic bus number
 * @adapter: the adapter to add
 * Context: can sleep
 *
 * This routine is used to declare an I2C adapter when its bus number
 * doesn't matter or when its bus number is specified by an dt alias.
 * Examples of bases when the bus number doesn't matter: I2C adapters
 * dynamically added by USB links or PCI plugin cards.
 *
 * When this returns zero, a new bus number was allocated and stored
 * in adap->nr, and the specified adapter became available for clients.
 * Otherwise, a negative errno value is returned.
 */
int i2c_add_adapter(struct i2c_adapter *adapter)
{
        struct device *dev = &adapter->dev;
        int id;

        if (dev->of_node) {
                id = of_alias_get_id(dev->of_node, "i2c");
                if (id >= 0) {
                        adapter->nr = id;
                        return __i2c_add_numbered_adapter(adapter);
                }
        }

        mutex_lock(&core_lock);
        id = idr_alloc(&i2c_adapter_idr, adapter,
                       __i2c_first_dynamic_bus_num, 0, GFP_KERNEL);
        mutex_unlock(&core_lock);
        if (WARN(id < 0, "couldn't get idr"))
                return id;

        adapter->nr = id;

        return i2c_register_adapter(adapter);
}
EXPORT_SYMBOL(i2c_add_adapter);

/**
 * i2c_add_numbered_adapter - declare i2c adapter, use static bus number
 * @adap: the adapter to register (with adap->nr initialized)
 * Context: can sleep
 *
 * This routine is used to declare an I2C adapter when its bus number
 * matters.  For example, use it for I2C adapters from system-on-chip CPUs,
 * or otherwise built in to the system's mainboard, and where i2c_board_info
 * is used to properly configure I2C devices.
 *
 * If the requested bus number is set to -1, then this function will behave
 * identically to i2c_add_adapter, and will dynamically assign a bus number.
 *
 * If no devices have pre-been declared for this bus, then be sure to
 * register the adapter before any dynamically allocated ones.  Otherwise
 * the required bus ID may not be available.
 *
 * When this returns zero, the specified adapter became available for
 * clients using the bus number provided in adap->nr.  Also, the table
 * of I2C devices pre-declared using i2c_register_board_info() is scanned,
 * and the appropriate driver model device nodes are created.  Otherwise, a
 * negative errno value is returned.
 */
int i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
        if (adap->nr == -1) /* -1 means dynamically assign bus id */
                return i2c_add_adapter(adap);

        return __i2c_add_numbered_adapter(adap);
}
EXPORT_SYMBOL_GPL(i2c_add_numbered_adapter);

static void i2c_do_del_adapter(struct i2c_driver *driver,
                              struct i2c_adapter *adapter)
{
        struct i2c_client *client, *_n;

        /* Remove the devices we created ourselves as the result of hardware
         * probing (using a driver's detect method) */
        list_for_each_entry_safe(client, _n, &driver->clients, detected) {
                if (client->adapter == adapter) {
                        dev_dbg(&adapter->dev, "Removing %s at 0x%x\n",
                                client->name, client->addr);
                        list_del(&client->detected);
                        i2c_unregister_device(client);
                }
        }
}

static int __unregister_client(struct device *dev, void *dummy)
{
        struct i2c_client *client = i2c_verify_client(dev);
        if (client && strcmp(client->name, "dummy"))
                i2c_unregister_device(client);
        return 0;
}

static int __unregister_dummy(struct device *dev, void *dummy)
{
        struct i2c_client *client = i2c_verify_client(dev);
        i2c_unregister_device(client);
        return 0;
}

static int __process_removed_adapter(struct device_driver *d, void *data)
{
        i2c_do_del_adapter(to_i2c_driver(d), data);
        return 0;
}

/**
 * i2c_del_adapter - unregister I2C adapter
 * @adap: the adapter being unregistered
 * Context: can sleep
 *
 * This unregisters an I2C adapter which was previously registered
 * by @i2c_add_adapter or @i2c_add_numbered_adapter.
 */
void i2c_del_adapter(struct i2c_adapter *adap)
{
        struct i2c_adapter *found;
        struct i2c_client *client, *next;

        /* First make sure that this adapter was ever added */
        mutex_lock(&core_lock);
        found = idr_find(&i2c_adapter_idr, adap->nr);
        mutex_unlock(&core_lock);
        if (found != adap) {
                pr_debug("attempting to delete unregistered adapter [%s]\n", adap->name);
                return;
        }

        i2c_acpi_remove_space_handler(adap);
        /* Tell drivers about this removal */
        mutex_lock(&core_lock);
        bus_for_each_drv(&i2c_bus_type, NULL, adap,
                               __process_removed_adapter);
        mutex_unlock(&core_lock);

        /* Remove devices instantiated from sysfs */
        mutex_lock_nested(&adap->userspace_clients_lock,
                          i2c_adapter_depth(adap));
        list_for_each_entry_safe(client, next, &adap->userspace_clients,
                                 detected) {
                dev_dbg(&adap->dev, "Removing %s at 0x%x\n", client->name,
                        client->addr);
                list_del(&client->detected);
                i2c_unregister_device(client);
        }
        mutex_unlock(&adap->userspace_clients_lock);

        /* Detach any active clients. This can't fail, thus we do not
         * check the returned value. This is a two-pass process, because
         * we can't remove the dummy devices during the first pass: they
         * could have been instantiated by real devices wishing to clean
         * them up properly, so we give them a chance to do that first. */
        device_for_each_child(&adap->dev, NULL, __unregister_client);
        device_for_each_child(&adap->dev, NULL, __unregister_dummy);

#ifdef CONFIG_I2C_COMPAT
        class_compat_remove_link(i2c_adapter_compat_class, &adap->dev,
                                 adap->dev.parent);
#endif

        /* device name is gone after device_unregister */
        dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);

        pm_runtime_disable(&adap->dev);

        i2c_host_notify_irq_teardown(adap);

        /* wait until all references to the device are gone
         *
         * FIXME: This is old code and should ideally be replaced by an
         * alternative which results in decoupling the lifetime of the struct
         * device from the i2c_adapter, like spi or netdev do. Any solution
         * should be thoroughly tested with DEBUG_KOBJECT_RELEASE enabled!
         */
        init_completion(&adap->dev_released);
        device_unregister(&adap->dev);
        wait_for_completion(&adap->dev_released);

        /* free bus id */
        mutex_lock(&core_lock);
        idr_remove(&i2c_adapter_idr, adap->nr);
        mutex_unlock(&core_lock);

        /* Clear the device structure in case this adapter is ever going to be
           added again */
        memset(&adap->dev, 0, sizeof(adap->dev));
}
EXPORT_SYMBOL(i2c_del_adapter);

/**
 * i2c_parse_fw_timings - get I2C related timing parameters from firmware
 * @dev: The device to scan for I2C timing properties
 * @t: the i2c_timings struct to be filled with values
 * @use_defaults: bool to use sane defaults derived from the I2C specification
 *                when properties are not found, otherwise use 0
 *
 * Scan the device for the generic I2C properties describing timing parameters
 * for the signal and fill the given struct with the results. If a property was
 * not found and use_defaults was true, then maximum timings are assumed which
 * are derived from the I2C specification. If use_defaults is not used, the
 * results will be 0, so drivers can apply their own defaults later. The latter
 * is mainly intended for avoiding regressions of existing drivers which want
 * to switch to this function. New drivers almost always should use the defaults.
 */

void i2c_parse_fw_timings(struct device *dev, struct i2c_timings *t, bool use_defaults)
{
        int ret;

        memset(t, 0, sizeof(*t));

        ret = device_property_read_u32(dev, "clock-frequency", &t->bus_freq_hz);
        if (ret && use_defaults)
                t->bus_freq_hz = 100000;

        ret = device_property_read_u32(dev, "i2c-scl-rising-time-ns", &t->scl_rise_ns);
        if (ret && use_defaults) {
                if (t->bus_freq_hz <= 100000)
                        t->scl_rise_ns = 1000;
                else if (t->bus_freq_hz <= 400000)
                        t->scl_rise_ns = 300;
                else
                        t->scl_rise_ns = 120;
        }

        ret = device_property_read_u32(dev, "i2c-scl-falling-time-ns", &t->scl_fall_ns);
        if (ret && use_defaults) {
                if (t->bus_freq_hz <= 400000)
                        t->scl_fall_ns = 300;
                else
                        t->scl_fall_ns = 120;
        }

        device_property_read_u32(dev, "i2c-scl-internal-delay-ns", &t->scl_int_delay_ns);

        ret = device_property_read_u32(dev, "i2c-sda-falling-time-ns", &t->sda_fall_ns);
        if (ret && use_defaults)
                t->sda_fall_ns = t->scl_fall_ns;

        device_property_read_u32(dev, "i2c-sda-hold-time-ns", &t->sda_hold_ns);
}
EXPORT_SYMBOL_GPL(i2c_parse_fw_timings);

/* ------------------------------------------------------------------------- */

int i2c_for_each_dev(void *data, int (*fn)(struct device *, void *))
{
        int res;

        mutex_lock(&core_lock);
        res = bus_for_each_dev(&i2c_bus_type, NULL, data, fn);
        mutex_unlock(&core_lock);

        return res;
}
EXPORT_SYMBOL_GPL(i2c_for_each_dev);

static int __process_new_driver(struct device *dev, void *data)
{
        if (dev->type != &i2c_adapter_type)
                return 0;
        return i2c_do_add_adapter(data, to_i2c_adapter(dev));
}

/*
 * An i2c_driver is used with one or more i2c_client (device) nodes to access
 * i2c slave chips, on a bus instance associated with some i2c_adapter.
 */

int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
        int res;

        /* Can't register until after driver model init */
        if (WARN_ON(!is_registered))
                return -EAGAIN;

        /* add the driver to the list of i2c drivers in the driver core */
        driver->driver.owner = owner;
        driver->driver.bus = &i2c_bus_type;
        INIT_LIST_HEAD(&driver->clients);

        /* When registration returns, the driver core
         * will have called probe() for all matching-but-unbound devices.
         */
        res = driver_register(&driver->driver);
        if (res)
                return res;

        pr_debug("driver [%s] registered\n", driver->driver.name);

        /* Walk the adapters that are already present */
        i2c_for_each_dev(driver, __process_new_driver);

        return 0;
}
EXPORT_SYMBOL(i2c_register_driver);

static int __process_removed_driver(struct device *dev, void *data)
{
        if (dev->type == &i2c_adapter_type)
                i2c_do_del_adapter(data, to_i2c_adapter(dev));
        return 0;
}

/**
 * i2c_del_driver - unregister I2C driver
 * @driver: the driver being unregistered
 * Context: can sleep
 */
void i2c_del_driver(struct i2c_driver *driver)
{
        i2c_for_each_dev(driver, __process_removed_driver);

        driver_unregister(&driver->driver);
        pr_debug("driver [%s] unregistered\n", driver->driver.name);
}
EXPORT_SYMBOL(i2c_del_driver);

/* ------------------------------------------------------------------------- */

/**
 * i2c_use_client - increments the reference count of the i2c client structure
 * @client: the client being referenced
 *
 * Each live reference to a client should be refcounted. The driver model does
 * that automatically as part of driver binding, so that most drivers don't
 * need to do this explicitly: they hold a reference until they're unbound
 * from the device.
 *
 * A pointer to the client with the incremented reference counter is returned.
 */
struct i2c_client *i2c_use_client(struct i2c_client *client)
{
        if (client && get_device(&client->dev))
                return client;
        return NULL;
}
EXPORT_SYMBOL(i2c_use_client);

/**
 * i2c_release_client - release a use of the i2c client structure
 * @client: the client being no longer referenced
 *
 * Must be called when a user of a client is finished with it.
 */
void i2c_release_client(struct i2c_client *client)
{
        if (client)
                put_device(&client->dev);
}
EXPORT_SYMBOL(i2c_release_client);

struct i2c_cmd_arg {
        unsigned        cmd;
        void            *arg;
};

static int i2c_cmd(struct device *dev, void *_arg)
{
        struct i2c_client       *client = i2c_verify_client(dev);
        struct i2c_cmd_arg      *arg = _arg;
        struct i2c_driver       *driver;

        if (!client || !client->dev.driver)
                return 0;

        driver = to_i2c_driver(client->dev.driver);
        if (driver->command)
                driver->command(client, arg->cmd, arg->arg);
        return 0;
}

void i2c_clients_command(struct i2c_adapter *adap, unsigned int cmd, void *arg)
{
        struct i2c_cmd_arg      cmd_arg;

        cmd_arg.cmd = cmd;
        cmd_arg.arg = arg;
        device_for_each_child(&adap->dev, &cmd_arg, i2c_cmd);
}
EXPORT_SYMBOL(i2c_clients_command);

static int __init i2c_init(void)
{
        int retval;

        retval = of_alias_get_highest_id("i2c");

        down_write(&__i2c_board_lock);
        if (retval >= __i2c_first_dynamic_bus_num)
                __i2c_first_dynamic_bus_num = retval + 1;
        up_write(&__i2c_board_lock);

        retval = bus_register(&i2c_bus_type);
        if (retval)
                return retval;

        is_registered = true;

#ifdef CONFIG_I2C_COMPAT
        i2c_adapter_compat_class = class_compat_register("i2c-adapter");
        if (!i2c_adapter_compat_class) {
                retval = -ENOMEM;
                goto bus_err;
        }
#endif
        retval = i2c_add_driver(&dummy_driver);
        if (retval)
                goto class_err;

        if (IS_ENABLED(CONFIG_OF_DYNAMIC))
                WARN_ON(of_reconfig_notifier_register(&i2c_of_notifier));
        if (IS_ENABLED(CONFIG_ACPI))
                WARN_ON(acpi_reconfig_notifier_register(&i2c_acpi_notifier));

        return 0;

class_err:
#ifdef CONFIG_I2C_COMPAT
        class_compat_unregister(i2c_adapter_compat_class);
bus_err:
#endif
        is_registered = false;
        bus_unregister(&i2c_bus_type);
        return retval;
}

static void __exit i2c_exit(void)
{
        if (IS_ENABLED(CONFIG_ACPI))
                WARN_ON(acpi_reconfig_notifier_unregister(&i2c_acpi_notifier));
        if (IS_ENABLED(CONFIG_OF_DYNAMIC))
                WARN_ON(of_reconfig_notifier_unregister(&i2c_of_notifier));
        i2c_del_driver(&dummy_driver);
#ifdef CONFIG_I2C_COMPAT
        class_compat_unregister(i2c_adapter_compat_class);
#endif
        bus_unregister(&i2c_bus_type);
        tracepoint_synchronize_unregister();
}

/* We must initialize early, because some subsystems register i2c drivers
 * in subsys_initcall() code, but are linked (and initialized) before i2c.
 */
postcore_initcall(i2c_init);
module_exit(i2c_exit);

/* ----------------------------------------------------
 * the functional interface to the i2c busses.
 * ----------------------------------------------------
 */

/* Check if val is exceeding the quirk IFF quirk is non 0 */
#define i2c_quirk_exceeded(val, quirk) ((quirk) && ((val) > (quirk)))

static int i2c_quirk_error(struct i2c_adapter *adap, struct i2c_msg *msg, char *err_msg)
{
        dev_err_ratelimited(&adap->dev, "adapter quirk: %s (addr 0x%04x, size %u, %s)\n",
                            err_msg, msg->addr, msg->len,
                            msg->flags & I2C_M_RD ? "read" : "write");
        return -EOPNOTSUPP;
}

static int i2c_check_for_quirks(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
        const struct i2c_adapter_quirks *q = adap->quirks;
        int max_num = q->max_num_msgs, i;
        bool do_len_check = true;

        if (q->flags & I2C_AQ_COMB) {
                max_num = 2;

                /* special checks for combined messages */
                if (num == 2) {
                        if (q->flags & I2C_AQ_COMB_WRITE_FIRST && msgs[0].flags & I2C_M_RD)
                                return i2c_quirk_error(adap, &msgs[0], "1st comb msg must be write");

                        if (q->flags & I2C_AQ_COMB_READ_SECOND && !(msgs[1].flags & I2C_M_RD))
                                return i2c_quirk_error(adap, &msgs[1], "2nd comb msg must be read");

                        if (q->flags & I2C_AQ_COMB_SAME_ADDR && msgs[0].addr != msgs[1].addr)
                                return i2c_quirk_error(adap, &msgs[0], "comb msg only to same addr");

                        if (i2c_quirk_exceeded(msgs[0].len, q->max_comb_1st_msg_len))
                                return i2c_quirk_error(adap, &msgs[0], "msg too long");

                        if (i2c_quirk_exceeded(msgs[1].len, q->max_comb_2nd_msg_len))
                                return i2c_quirk_error(adap, &msgs[1], "msg too long");

                        do_len_check = false;
                }
        }

        if (i2c_quirk_exceeded(num, max_num))
                return i2c_quirk_error(adap, &msgs[0], "too many messages");

        for (i = 0; i < num; i++) {
                u16 len = msgs[i].len;

                if (msgs[i].flags & I2C_M_RD) {
                        if (do_len_check && i2c_quirk_exceeded(len, q->max_read_len))
                                return i2c_quirk_error(adap, &msgs[i], "msg too long");

                        if (q->flags & I2C_AQ_NO_ZERO_LEN_READ && len == 0)
                                return i2c_quirk_error(adap, &msgs[i], "no zero length");
                } else {
                        if (do_len_check && i2c_quirk_exceeded(len, q->max_write_len))
                                return i2c_quirk_error(adap, &msgs[i], "msg too long");

                        if (q->flags & I2C_AQ_NO_ZERO_LEN_WRITE && len == 0)
                                return i2c_quirk_error(adap, &msgs[i], "no zero length");
                }
        }

        return 0;
}

/**
 * __i2c_transfer - unlocked flavor of i2c_transfer
 * @adap: Handle to I2C bus
 * @msgs: One or more messages to execute before STOP is issued to
 *      terminate the operation; each message begins with a START.
 * @num: Number of messages to be executed.
 *
 * Returns negative errno, else the number of messages executed.
 *
 * Adapter lock must be held when calling this function. No debug logging
 * takes place. adap->algo->master_xfer existence isn't checked.
 */
int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
        unsigned long orig_jiffies;
        int ret, try;

        if (WARN_ON(!msgs || num < 1))
                return -EINVAL;

        if (adap->quirks && i2c_check_for_quirks(adap, msgs, num))
                return -EOPNOTSUPP;

        /*
         * i2c_trace_msg_key gets enabled when tracepoint i2c_transfer gets
         * enabled.  This is an efficient way of keeping the for-loop from
         * being executed when not needed.
         */
        if (static_branch_unlikely(&i2c_trace_msg_key)) {
                int i;
                for (i = 0; i < num; i++)
                        if (msgs[i].flags & I2C_M_RD)
                                trace_i2c_read(adap, &msgs[i], i);
                        else
                                trace_i2c_write(adap, &msgs[i], i);
        }

        /* Retry automatically on arbitration loss */
        orig_jiffies = jiffies;
        for (ret = 0, try = 0; try <= adap->retries; try++) {
                ret = adap->algo->master_xfer(adap, msgs, num);
                if (ret != -EAGAIN)
                        break;
                if (time_after(jiffies, orig_jiffies + adap->timeout))
                        break;
        }

        if (static_branch_unlikely(&i2c_trace_msg_key)) {
                int i;
                for (i = 0; i < ret; i++)
                        if (msgs[i].flags & I2C_M_RD)
                                trace_i2c_reply(adap, &msgs[i], i);
                trace_i2c_result(adap, num, ret);
        }

        return ret;
}
EXPORT_SYMBOL(__i2c_transfer);

/**
 * i2c_transfer - execute a single or combined I2C message
 * @adap: Handle to I2C bus
 * @msgs: One or more messages to execute before STOP is issued to
 *      terminate the operation; each message begins with a START.
 * @num: Number of messages to be executed.
 *
 * Returns negative errno, else the number of messages executed.
 *
 * Note that there is no requirement that each message be sent to
 * the same slave address, although that is the most common model.
 */
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
        int ret;

        /* REVISIT the fault reporting model here is weak:
         *
         *  - When we get an error after receiving N bytes from a slave,
         *    there is no way to report "N".
         *
         *  - When we get a NAK after transmitting N bytes to a slave,
         *    there is no way to report "N" ... or to let the master
         *    continue executing the rest of this combined message, if
         *    that's the appropriate response.
         *
         *  - When for example "num" is two and we successfully complete
         *    the first message but get an error part way through the
         *    second, it's unclear whether that should be reported as
         *    one (discarding status on the second message) or errno
         *    (discarding status on the first one).
         */

        if (adap->algo->master_xfer) {
#ifdef DEBUG
                for (ret = 0; ret < num; ret++) {
                        dev_dbg(&adap->dev,
                                "master_xfer[%d] %c, addr=0x%02x, len=%d%s\n",
                                ret, (msgs[ret].flags & I2C_M_RD) ? 'R' : 'W',
                                msgs[ret].addr, msgs[ret].len,
                                (msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");
                }
#endif

                if (in_atomic() || irqs_disabled()) {
                        ret = i2c_trylock_bus(adap, I2C_LOCK_SEGMENT);
                        if (!ret)
                                /* I2C activity is ongoing. */
                                return -EAGAIN;
                } else {
                        i2c_lock_bus(adap, I2C_LOCK_SEGMENT);
                }

                ret = __i2c_transfer(adap, msgs, num);
                i2c_unlock_bus(adap, I2C_LOCK_SEGMENT);

                return ret;
        } else {
                dev_dbg(&adap->dev, "I2C level transfers not supported\n");
                return -EOPNOTSUPP;
        }
}
EXPORT_SYMBOL(i2c_transfer);

/**
 * i2c_transfer_buffer_flags - issue a single I2C message transferring data
 *                             to/from a buffer
 * @client: Handle to slave device
 * @buf: Where the data is stored
 * @count: How many bytes to transfer, must be less than 64k since msg.len is u16
 * @flags: The flags to be used for the message, e.g. I2C_M_RD for reads
 *
 * Returns negative errno, or else the number of bytes transferred.
 */
int i2c_transfer_buffer_flags(const struct i2c_client *client, char *buf,
                              int count, u16 flags)
{
        int ret;
        struct i2c_msg msg = {
                .addr = client->addr,
                .flags = flags | (client->flags & I2C_M_TEN),
                .len = count,
                .buf = buf,
        };

        ret = i2c_transfer(client->adapter, &msg, 1);

        /*
         * If everything went ok (i.e. 1 msg transferred), return #bytes
         * transferred, else error code.
         */
        return (ret == 1) ? count : ret;
}
EXPORT_SYMBOL(i2c_transfer_buffer_flags);

/**
 * i2c_get_device_id - get manufacturer, part id and die revision of a device
 * @client: The device to query
 * @id: The queried information
 *
 * Returns negative errno on error, zero on success.
 */
int i2c_get_device_id(const struct i2c_client *client,
                      struct i2c_device_identity *id)
{
        struct i2c_adapter *adap = client->adapter;
        union i2c_smbus_data raw_id;
        int ret;

        if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_READ_I2C_BLOCK))
                return -EOPNOTSUPP;

        raw_id.block[0] = 3;
        ret = i2c_smbus_xfer(adap, I2C_ADDR_DEVICE_ID, 0,
                             I2C_SMBUS_READ, client->addr << 1,
                             I2C_SMBUS_I2C_BLOCK_DATA, &raw_id);
        if (ret)
                return ret;

        id->manufacturer_id = (raw_id.block[1] << 4) | (raw_id.block[2] >> 4);
        id->part_id = ((raw_id.block[2] & 0xf) << 5) | (raw_id.block[3] >> 3);
        id->die_revision = raw_id.block[3] & 0x7;
        return 0;
}
EXPORT_SYMBOL_GPL(i2c_get_device_id);

/* ----------------------------------------------------
 * the i2c address scanning function
 * Will not work for 10-bit addresses!
 * ----------------------------------------------------
 */

/*
 * Legacy default probe function, mostly relevant for SMBus. The default
 * probe method is a quick write, but it is known to corrupt the 24RF08
 * EEPROMs due to a state machine bug, and could also irreversibly
 * write-protect some EEPROMs, so for address ranges 0x30-0x37 and 0x50-0x5f,
 * we use a short byte read instead. Also, some bus drivers don't implement
 * quick write, so we fallback to a byte read in that case too.
 * On x86, there is another special case for FSC hardware monitoring chips,
 * which want regular byte reads (address 0x73.) Fortunately, these are the
 * only known chips using this I2C address on PC hardware.
 * Returns 1 if probe succeeded, 0 if not.
 */
static int i2c_default_probe(struct i2c_adapter *adap, unsigned short addr)
{
        int err;
        union i2c_smbus_data dummy;

#ifdef CONFIG_X86
        if (addr == 0x73 && (adap->class & I2C_CLASS_HWMON)
         && i2c_check_functionality(adap, I2C_FUNC_SMBUS_READ_BYTE_DATA))
                err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, 0,
                                     I2C_SMBUS_BYTE_DATA, &dummy);
        else
#endif
        if (!((addr & ~0x07) == 0x30 || (addr & ~0x0f) == 0x50)
         && i2c_check_functionality(adap, I2C_FUNC_SMBUS_QUICK))
                err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_WRITE, 0,
                                     I2C_SMBUS_QUICK, NULL);
        else if (i2c_check_functionality(adap, I2C_FUNC_SMBUS_READ_BYTE))
                err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, 0,
                                     I2C_SMBUS_BYTE, &dummy);
        else {
                dev_warn(&adap->dev, "No suitable probing method supported for address 0x%02X\n",
                         addr);
                err = -EOPNOTSUPP;
        }

        return err >= 0;
}

static int i2c_detect_address(struct i2c_client *temp_client,
                              struct i2c_driver *driver)
{
        struct i2c_board_info info;
        struct i2c_adapter *adapter = temp_client->adapter;
        int addr = temp_client->addr;
        int err;

        /* Make sure the address is valid */
        err = i2c_check_7bit_addr_validity_strict(addr);
        if (err) {
                dev_warn(&adapter->dev, "Invalid probe address 0x%02x\n",
                         addr);
                return err;
        }

        /* Skip if already in use (7 bit, no need to encode flags) */
        if (i2c_check_addr_busy(adapter, addr))
                return 0;

        /* Make sure there is something at this address */
        if (!i2c_default_probe(adapter, addr))
                return 0;

        /* Finally call the custom detection function */
        memset(&info, 0, sizeof(struct i2c_board_info));
        info.addr = addr;
        err = driver->detect(temp_client, &info);
        if (err) {
                /* -ENODEV is returned if the detection fails. We catch it
                   here as this isn't an error. */
                return err == -ENODEV ? 0 : err;
        }

        /* Consistency check */
        if (info.type[0] == '\0') {
                dev_err(&adapter->dev,
                        "%s detection function provided no name for 0x%x\n",
                        driver->driver.name, addr);
        } else {
                struct i2c_client *client;

                /* Detection succeeded, instantiate the device */
                if (adapter->class & I2C_CLASS_DEPRECATED)
                        dev_warn(&adapter->dev,
                                "This adapter will soon drop class based instantiation of devices. "
                                "Please make sure client 0x%02x gets instantiated by other means. "
                                "Check 'Documentation/i2c/instantiating-devices' for details.\n",
                                info.addr);

                dev_dbg(&adapter->dev, "Creating %s at 0x%02x\n",
                        info.type, info.addr);
                client = i2c_new_device(adapter, &info);
                if (client)
                        list_add_tail(&client->detected, &driver->clients);
                else
                        dev_err(&adapter->dev, "Failed creating %s at 0x%02x\n",
                                info.type, info.addr);
        }
        return 0;
}

static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver)
{
        const unsigned short *address_list;
        struct i2c_client *temp_client;
        int i, err = 0;
        int adap_id = i2c_adapter_id(adapter);

        address_list = driver->address_list;
        if (!driver->detect || !address_list)
                return 0;

        /* Warn that the adapter lost class based instantiation */
        if (adapter->class == I2C_CLASS_DEPRECATED) {
                dev_dbg(&adapter->dev,
                        "This adapter dropped support for I2C classes and won't auto-detect %s devices anymore. "
                        "If you need it, check 'Documentation/i2c/instantiating-devices' for alternatives.\n",
                        driver->driver.name);
                return 0;
        }

        /* Stop here if the classes do not match */
        if (!(adapter->class & driver->class))
                return 0;

        /* Set up a temporary client to help detect callback */
        temp_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
        if (!temp_client)
                return -ENOMEM;
        temp_client->adapter = adapter;

        for (i = 0; address_list[i] != I2C_CLIENT_END; i += 1) {
                dev_dbg(&adapter->dev,
                        "found normal entry for adapter %d, addr 0x%02x\n",
                        adap_id, address_list[i]);
                temp_client->addr = address_list[i];
                err = i2c_detect_address(temp_client, driver);
                if (unlikely(err))
                        break;
        }

        kfree(temp_client);
        return err;
}

int i2c_probe_func_quick_read(struct i2c_adapter *adap, unsigned short addr)
{
        return i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, 0,
                              I2C_SMBUS_QUICK, NULL) >= 0;
}
EXPORT_SYMBOL_GPL(i2c_probe_func_quick_read);

struct i2c_client *
i2c_new_probed_device(struct i2c_adapter *adap,
                      struct i2c_board_info *info,
                      unsigned short const *addr_list,
                      int (*probe)(struct i2c_adapter *, unsigned short addr))
{
        int i;

        if (!probe)
                probe = i2c_default_probe;

        for (i = 0; addr_list[i] != I2C_CLIENT_END; i++) {
                /* Check address validity */
                if (i2c_check_7bit_addr_validity_strict(addr_list[i]) < 0) {
                        dev_warn(&adap->dev, "Invalid 7-bit address 0x%02x\n",
                                 addr_list[i]);
                        continue;
                }

                /* Check address availability (7 bit, no need to encode flags) */
                if (i2c_check_addr_busy(adap, addr_list[i])) {
                        dev_dbg(&adap->dev,
                                "Address 0x%02x already in use, not probing\n",
                                addr_list[i]);
                        continue;
                }

                /* Test address responsiveness */
                if (probe(adap, addr_list[i]))
                        break;
        }

        if (addr_list[i] == I2C_CLIENT_END) {
                dev_dbg(&adap->dev, "Probing failed, no device found\n");
                return NULL;
        }

        info->addr = addr_list[i];
        return i2c_new_device(adap, info);
}
EXPORT_SYMBOL_GPL(i2c_new_probed_device);

struct i2c_adapter *i2c_get_adapter(int nr)
{
        struct i2c_adapter *adapter;

        mutex_lock(&core_lock);
        adapter = idr_find(&i2c_adapter_idr, nr);
        if (!adapter)
                goto exit;

        if (try_module_get(adapter->owner))
                get_device(&adapter->dev);
        else
                adapter = NULL;

 exit:
        mutex_unlock(&core_lock);
        return adapter;
}
EXPORT_SYMBOL(i2c_get_adapter);

void i2c_put_adapter(struct i2c_adapter *adap)
{
        if (!adap)
                return;

        put_device(&adap->dev);
        module_put(adap->owner);
}
EXPORT_SYMBOL(i2c_put_adapter);

/**
 * i2c_get_dma_safe_msg_buf() - get a DMA safe buffer for the given i2c_msg
 * @msg: the message to be checked
 * @threshold: the minimum number of bytes for which using DMA makes sense
 *
 * Return: NULL if a DMA safe buffer was not obtained. Use msg->buf with PIO.
 *         Or a valid pointer to be used with DMA. After use, release it by
 *         calling i2c_put_dma_safe_msg_buf().
 *
 * This function must only be called from process context!
 */
u8 *i2c_get_dma_safe_msg_buf(struct i2c_msg *msg, unsigned int threshold)
{
        if (msg->len < threshold)
                return NULL;

        if (msg->flags & I2C_M_DMA_SAFE)
                return msg->buf;

        pr_debug("using bounce buffer for addr=0x%02x, len=%d\n",
                 msg->addr, msg->len);

        if (msg->flags & I2C_M_RD)
                return kzalloc(msg->len, GFP_KERNEL);
        else
                return kmemdup(msg->buf, msg->len, GFP_KERNEL);
}
EXPORT_SYMBOL_GPL(i2c_get_dma_safe_msg_buf);

/**
 * i2c_put_dma_safe_msg_buf - release DMA safe buffer and sync with i2c_msg
 * @buf: the buffer obtained from i2c_get_dma_safe_msg_buf(). May be NULL.
 * @msg: the message which the buffer corresponds to
 * @xferred: bool saying if the message was transferred
 */
void i2c_put_dma_safe_msg_buf(u8 *buf, struct i2c_msg *msg, bool xferred)
{
        if (!buf || buf == msg->buf)
                return;

        if (xferred && msg->flags & I2C_M_RD)
                memcpy(msg->buf, buf, msg->len);

        kfree(buf);
}
EXPORT_SYMBOL_GPL(i2c_put_dma_safe_msg_buf);

MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
MODULE_DESCRIPTION("I2C-Bus main module");
MODULE_LICENSE("GPL");