Linux 4.16.11

[linux/fpc-iii.git] / drivers / spi / spidev.c

/*
 * Simple synchronous userspace interface to SPI devices
 *
 * Copyright (C) 2006 SWAPP
 *      Andrea Paterniani <a.paterniani@swapp-eng.it>
 * Copyright (C) 2007 David Brownell (simplification, cleanup)
 *
 * 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.
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/ioctl.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/list.h>
#include <linux/errno.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/compat.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/acpi.h>

#include <linux/spi/spi.h>
#include <linux/spi/spidev.h>

#include <linux/uaccess.h>


/*
 * This supports access to SPI devices using normal userspace I/O calls.
 * Note that while traditional UNIX/POSIX I/O semantics are half duplex,
 * and often mask message boundaries, full SPI support requires full duplex
 * transfers.  There are several kinds of internal message boundaries to
 * handle chipselect management and other protocol options.
 *
 * SPI has a character major number assigned.  We allocate minor numbers
 * dynamically using a bitmask.  You must use hotplug tools, such as udev
 * (or mdev with busybox) to create and destroy the /dev/spidevB.C device
 * nodes, since there is no fixed association of minor numbers with any
 * particular SPI bus or device.
 */
#define SPIDEV_MAJOR                    153     /* assigned */
#define N_SPI_MINORS                    32      /* ... up to 256 */

static DECLARE_BITMAP(minors, N_SPI_MINORS);


/* Bit masks for spi_device.mode management.  Note that incorrect
 * settings for some settings can cause *lots* of trouble for other
 * devices on a shared bus:
 *
 *  - CS_HIGH ... this device will be active when it shouldn't be
 *  - 3WIRE ... when active, it won't behave as it should
 *  - NO_CS ... there will be no explicit message boundaries; this
 *      is completely incompatible with the shared bus model
 *  - READY ... transfers may proceed when they shouldn't.
 *
 * REVISIT should changing those flags be privileged?
 */
#define SPI_MODE_MASK           (SPI_CPHA | SPI_CPOL | SPI_CS_HIGH \
                                | SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP \
                                | SPI_NO_CS | SPI_READY | SPI_TX_DUAL \
                                | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD)

struct spidev_data {
        dev_t                   devt;
        spinlock_t              spi_lock;
        struct spi_device       *spi;
        struct list_head        device_entry;

        /* TX/RX buffers are NULL unless this device is open (users > 0) */
        struct mutex            buf_lock;
        unsigned                users;
        u8                      *tx_buffer;
        u8                      *rx_buffer;
        u32                     speed_hz;
};

static LIST_HEAD(device_list);
static DEFINE_MUTEX(device_list_lock);

static unsigned bufsiz = 4096;
module_param(bufsiz, uint, S_IRUGO);
MODULE_PARM_DESC(bufsiz, "data bytes in biggest supported SPI message");

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

static ssize_t
spidev_sync(struct spidev_data *spidev, struct spi_message *message)
{
        int status;
        struct spi_device *spi;

        spin_lock_irq(&spidev->spi_lock);
        spi = spidev->spi;
        spin_unlock_irq(&spidev->spi_lock);

        if (spi == NULL)
                status = -ESHUTDOWN;
        else
                status = spi_sync(spi, message);

        if (status == 0)
                status = message->actual_length;

        return status;
}

static inline ssize_t
spidev_sync_write(struct spidev_data *spidev, size_t len)
{
        struct spi_transfer     t = {
                        .tx_buf         = spidev->tx_buffer,
                        .len            = len,
                        .speed_hz       = spidev->speed_hz,
                };
        struct spi_message      m;

        spi_message_init(&m);
        spi_message_add_tail(&t, &m);
        return spidev_sync(spidev, &m);
}

static inline ssize_t
spidev_sync_read(struct spidev_data *spidev, size_t len)
{
        struct spi_transfer     t = {
                        .rx_buf         = spidev->rx_buffer,
                        .len            = len,
                        .speed_hz       = spidev->speed_hz,
                };
        struct spi_message      m;

        spi_message_init(&m);
        spi_message_add_tail(&t, &m);
        return spidev_sync(spidev, &m);
}

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

/* Read-only message with current device setup */
static ssize_t
spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
        struct spidev_data      *spidev;
        ssize_t                 status = 0;

        /* chipselect only toggles at start or end of operation */
        if (count > bufsiz)
                return -EMSGSIZE;

        spidev = filp->private_data;

        mutex_lock(&spidev->buf_lock);
        status = spidev_sync_read(spidev, count);
        if (status > 0) {
                unsigned long   missing;

                missing = copy_to_user(buf, spidev->rx_buffer, status);
                if (missing == status)
                        status = -EFAULT;
                else
                        status = status - missing;
        }
        mutex_unlock(&spidev->buf_lock);

        return status;
}

/* Write-only message with current device setup */
static ssize_t
spidev_write(struct file *filp, const char __user *buf,
                size_t count, loff_t *f_pos)
{
        struct spidev_data      *spidev;
        ssize_t                 status = 0;
        unsigned long           missing;

        /* chipselect only toggles at start or end of operation */
        if (count > bufsiz)
                return -EMSGSIZE;

        spidev = filp->private_data;

        mutex_lock(&spidev->buf_lock);
        missing = copy_from_user(spidev->tx_buffer, buf, count);
        if (missing == 0)
                status = spidev_sync_write(spidev, count);
        else
                status = -EFAULT;
        mutex_unlock(&spidev->buf_lock);

        return status;
}

static int spidev_message(struct spidev_data *spidev,
                struct spi_ioc_transfer *u_xfers, unsigned n_xfers)
{
        struct spi_message      msg;
        struct spi_transfer     *k_xfers;
        struct spi_transfer     *k_tmp;
        struct spi_ioc_transfer *u_tmp;
        unsigned                n, total, tx_total, rx_total;
        u8                      *tx_buf, *rx_buf;
        int                     status = -EFAULT;

        spi_message_init(&msg);
        k_xfers = kcalloc(n_xfers, sizeof(*k_tmp), GFP_KERNEL);
        if (k_xfers == NULL)
                return -ENOMEM;

        /* Construct spi_message, copying any tx data to bounce buffer.
         * We walk the array of user-provided transfers, using each one
         * to initialize a kernel version of the same transfer.
         */
        tx_buf = spidev->tx_buffer;
        rx_buf = spidev->rx_buffer;
        total = 0;
        tx_total = 0;
        rx_total = 0;
        for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
                        n;
                        n--, k_tmp++, u_tmp++) {
                k_tmp->len = u_tmp->len;

                total += k_tmp->len;
                /* Since the function returns the total length of transfers
                 * on success, restrict the total to positive int values to
                 * avoid the return value looking like an error.  Also check
                 * each transfer length to avoid arithmetic overflow.
                 */
                if (total > INT_MAX || k_tmp->len > INT_MAX) {
                        status = -EMSGSIZE;
                        goto done;
                }

                if (u_tmp->rx_buf) {
                        /* this transfer needs space in RX bounce buffer */
                        rx_total += k_tmp->len;
                        if (rx_total > bufsiz) {
                                status = -EMSGSIZE;
                                goto done;
                        }
                        k_tmp->rx_buf = rx_buf;
                        rx_buf += k_tmp->len;
                }
                if (u_tmp->tx_buf) {
                        /* this transfer needs space in TX bounce buffer */
                        tx_total += k_tmp->len;
                        if (tx_total > bufsiz) {
                                status = -EMSGSIZE;
                                goto done;
                        }
                        k_tmp->tx_buf = tx_buf;
                        if (copy_from_user(tx_buf, (const u8 __user *)
                                                (uintptr_t) u_tmp->tx_buf,
                                        u_tmp->len))
                                goto done;
                        tx_buf += k_tmp->len;
                }

                k_tmp->cs_change = !!u_tmp->cs_change;
                k_tmp->tx_nbits = u_tmp->tx_nbits;
                k_tmp->rx_nbits = u_tmp->rx_nbits;
                k_tmp->bits_per_word = u_tmp->bits_per_word;
                k_tmp->delay_usecs = u_tmp->delay_usecs;
                k_tmp->speed_hz = u_tmp->speed_hz;
                if (!k_tmp->speed_hz)
                        k_tmp->speed_hz = spidev->speed_hz;
#ifdef VERBOSE
                dev_dbg(&spidev->spi->dev,
                        "  xfer len %u %s%s%s%dbits %u usec %uHz\n",
                        u_tmp->len,
                        u_tmp->rx_buf ? "rx " : "",
                        u_tmp->tx_buf ? "tx " : "",
                        u_tmp->cs_change ? "cs " : "",
                        u_tmp->bits_per_word ? : spidev->spi->bits_per_word,
                        u_tmp->delay_usecs,
                        u_tmp->speed_hz ? : spidev->spi->max_speed_hz);
#endif
                spi_message_add_tail(k_tmp, &msg);
        }

        status = spidev_sync(spidev, &msg);
        if (status < 0)
                goto done;

        /* copy any rx data out of bounce buffer */
        rx_buf = spidev->rx_buffer;
        for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {
                if (u_tmp->rx_buf) {
                        if (copy_to_user((u8 __user *)
                                        (uintptr_t) u_tmp->rx_buf, rx_buf,
                                        u_tmp->len)) {
                                status = -EFAULT;
                                goto done;
                        }
                        rx_buf += u_tmp->len;
                }
        }
        status = total;

done:
        kfree(k_xfers);
        return status;
}

static struct spi_ioc_transfer *
spidev_get_ioc_message(unsigned int cmd, struct spi_ioc_transfer __user *u_ioc,
                unsigned *n_ioc)
{
        u32     tmp;

        /* Check type, command number and direction */
        if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC
                        || _IOC_NR(cmd) != _IOC_NR(SPI_IOC_MESSAGE(0))
                        || _IOC_DIR(cmd) != _IOC_WRITE)
                return ERR_PTR(-ENOTTY);

        tmp = _IOC_SIZE(cmd);
        if ((tmp % sizeof(struct spi_ioc_transfer)) != 0)
                return ERR_PTR(-EINVAL);
        *n_ioc = tmp / sizeof(struct spi_ioc_transfer);
        if (*n_ioc == 0)
                return NULL;

        /* copy into scratch area */
        return memdup_user(u_ioc, tmp);
}

static long
spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
        int                     retval = 0;
        struct spidev_data      *spidev;
        struct spi_device       *spi;
        u32                     tmp;
        unsigned                n_ioc;
        struct spi_ioc_transfer *ioc;

        /* Check type and command number */
        if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC)
                return -ENOTTY;

        /* guard against device removal before, or while,
         * we issue this ioctl.
         */
        spidev = filp->private_data;
        spin_lock_irq(&spidev->spi_lock);
        spi = spi_dev_get(spidev->spi);
        spin_unlock_irq(&spidev->spi_lock);

        if (spi == NULL)
                return -ESHUTDOWN;

        /* use the buffer lock here for triple duty:
         *  - prevent I/O (from us) so calling spi_setup() is safe;
         *  - prevent concurrent SPI_IOC_WR_* from morphing
         *    data fields while SPI_IOC_RD_* reads them;
         *  - SPI_IOC_MESSAGE needs the buffer locked "normally".
         */
        mutex_lock(&spidev->buf_lock);

        switch (cmd) {
        /* read requests */
        case SPI_IOC_RD_MODE:
                retval = put_user(spi->mode & SPI_MODE_MASK,
                                        (__u8 __user *)arg);
                break;
        case SPI_IOC_RD_MODE32:
                retval = put_user(spi->mode & SPI_MODE_MASK,
                                        (__u32 __user *)arg);
                break;
        case SPI_IOC_RD_LSB_FIRST:
                retval = put_user((spi->mode & SPI_LSB_FIRST) ?  1 : 0,
                                        (__u8 __user *)arg);
                break;
        case SPI_IOC_RD_BITS_PER_WORD:
                retval = put_user(spi->bits_per_word, (__u8 __user *)arg);
                break;
        case SPI_IOC_RD_MAX_SPEED_HZ:
                retval = put_user(spidev->speed_hz, (__u32 __user *)arg);
                break;

        /* write requests */
        case SPI_IOC_WR_MODE:
        case SPI_IOC_WR_MODE32:
                if (cmd == SPI_IOC_WR_MODE)
                        retval = get_user(tmp, (u8 __user *)arg);
                else
                        retval = get_user(tmp, (u32 __user *)arg);
                if (retval == 0) {
                        u32     save = spi->mode;

                        if (tmp & ~SPI_MODE_MASK) {
                                retval = -EINVAL;
                                break;
                        }

                        tmp |= spi->mode & ~SPI_MODE_MASK;
                        spi->mode = (u16)tmp;
                        retval = spi_setup(spi);
                        if (retval < 0)
                                spi->mode = save;
                        else
                                dev_dbg(&spi->dev, "spi mode %x\n", tmp);
                }
                break;
        case SPI_IOC_WR_LSB_FIRST:
                retval = get_user(tmp, (__u8 __user *)arg);
                if (retval == 0) {
                        u32     save = spi->mode;

                        if (tmp)
                                spi->mode |= SPI_LSB_FIRST;
                        else
                                spi->mode &= ~SPI_LSB_FIRST;
                        retval = spi_setup(spi);
                        if (retval < 0)
                                spi->mode = save;
                        else
                                dev_dbg(&spi->dev, "%csb first\n",
                                                tmp ? 'l' : 'm');
                }
                break;
        case SPI_IOC_WR_BITS_PER_WORD:
                retval = get_user(tmp, (__u8 __user *)arg);
                if (retval == 0) {
                        u8      save = spi->bits_per_word;

                        spi->bits_per_word = tmp;
                        retval = spi_setup(spi);
                        if (retval < 0)
                                spi->bits_per_word = save;
                        else
                                dev_dbg(&spi->dev, "%d bits per word\n", tmp);
                }
                break;
        case SPI_IOC_WR_MAX_SPEED_HZ:
                retval = get_user(tmp, (__u32 __user *)arg);
                if (retval == 0) {
                        u32     save = spi->max_speed_hz;

                        spi->max_speed_hz = tmp;
                        retval = spi_setup(spi);
                        if (retval >= 0)
                                spidev->speed_hz = tmp;
                        else
                                dev_dbg(&spi->dev, "%d Hz (max)\n", tmp);
                        spi->max_speed_hz = save;
                }
                break;

        default:
                /* segmented and/or full-duplex I/O request */
                /* Check message and copy into scratch area */
                ioc = spidev_get_ioc_message(cmd,
                                (struct spi_ioc_transfer __user *)arg, &n_ioc);
                if (IS_ERR(ioc)) {
                        retval = PTR_ERR(ioc);
                        break;
                }
                if (!ioc)
                        break;  /* n_ioc is also 0 */

                /* translate to spi_message, execute */
                retval = spidev_message(spidev, ioc, n_ioc);
                kfree(ioc);
                break;
        }

        mutex_unlock(&spidev->buf_lock);
        spi_dev_put(spi);
        return retval;
}

#ifdef CONFIG_COMPAT
static long
spidev_compat_ioc_message(struct file *filp, unsigned int cmd,
                unsigned long arg)
{
        struct spi_ioc_transfer __user  *u_ioc;
        int                             retval = 0;
        struct spidev_data              *spidev;
        struct spi_device               *spi;
        unsigned                        n_ioc, n;
        struct spi_ioc_transfer         *ioc;

        u_ioc = (struct spi_ioc_transfer __user *) compat_ptr(arg);

        /* guard against device removal before, or while,
         * we issue this ioctl.
         */
        spidev = filp->private_data;
        spin_lock_irq(&spidev->spi_lock);
        spi = spi_dev_get(spidev->spi);
        spin_unlock_irq(&spidev->spi_lock);

        if (spi == NULL)
                return -ESHUTDOWN;

        /* SPI_IOC_MESSAGE needs the buffer locked "normally" */
        mutex_lock(&spidev->buf_lock);

        /* Check message and copy into scratch area */
        ioc = spidev_get_ioc_message(cmd, u_ioc, &n_ioc);
        if (IS_ERR(ioc)) {
                retval = PTR_ERR(ioc);
                goto done;
        }
        if (!ioc)
                goto done;      /* n_ioc is also 0 */

        /* Convert buffer pointers */
        for (n = 0; n < n_ioc; n++) {
                ioc[n].rx_buf = (uintptr_t) compat_ptr(ioc[n].rx_buf);
                ioc[n].tx_buf = (uintptr_t) compat_ptr(ioc[n].tx_buf);
        }

        /* translate to spi_message, execute */
        retval = spidev_message(spidev, ioc, n_ioc);
        kfree(ioc);

done:
        mutex_unlock(&spidev->buf_lock);
        spi_dev_put(spi);
        return retval;
}

static long
spidev_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
        if (_IOC_TYPE(cmd) == SPI_IOC_MAGIC
                        && _IOC_NR(cmd) == _IOC_NR(SPI_IOC_MESSAGE(0))
                        && _IOC_DIR(cmd) == _IOC_WRITE)
                return spidev_compat_ioc_message(filp, cmd, arg);

        return spidev_ioctl(filp, cmd, (unsigned long)compat_ptr(arg));
}
#else
#define spidev_compat_ioctl NULL
#endif /* CONFIG_COMPAT */

static int spidev_open(struct inode *inode, struct file *filp)
{
        struct spidev_data      *spidev;
        int                     status = -ENXIO;

        mutex_lock(&device_list_lock);

        list_for_each_entry(spidev, &device_list, device_entry) {
                if (spidev->devt == inode->i_rdev) {
                        status = 0;
                        break;
                }
        }

        if (status) {
                pr_debug("spidev: nothing for minor %d\n", iminor(inode));
                goto err_find_dev;
        }

        if (!spidev->tx_buffer) {
                spidev->tx_buffer = kmalloc(bufsiz, GFP_KERNEL);
                if (!spidev->tx_buffer) {
                        dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
                        status = -ENOMEM;
                        goto err_find_dev;
                }
        }

        if (!spidev->rx_buffer) {
                spidev->rx_buffer = kmalloc(bufsiz, GFP_KERNEL);
                if (!spidev->rx_buffer) {
                        dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
                        status = -ENOMEM;
                        goto err_alloc_rx_buf;
                }
        }

        spidev->users++;
        filp->private_data = spidev;
        nonseekable_open(inode, filp);

        mutex_unlock(&device_list_lock);
        return 0;

err_alloc_rx_buf:
        kfree(spidev->tx_buffer);
        spidev->tx_buffer = NULL;
err_find_dev:
        mutex_unlock(&device_list_lock);
        return status;
}

static int spidev_release(struct inode *inode, struct file *filp)
{
        struct spidev_data      *spidev;

        mutex_lock(&device_list_lock);
        spidev = filp->private_data;
        filp->private_data = NULL;

        /* last close? */
        spidev->users--;
        if (!spidev->users) {
                int             dofree;

                kfree(spidev->tx_buffer);
                spidev->tx_buffer = NULL;

                kfree(spidev->rx_buffer);
                spidev->rx_buffer = NULL;

                spin_lock_irq(&spidev->spi_lock);
                if (spidev->spi)
                        spidev->speed_hz = spidev->spi->max_speed_hz;

                /* ... after we unbound from the underlying device? */
                dofree = (spidev->spi == NULL);
                spin_unlock_irq(&spidev->spi_lock);

                if (dofree)
                        kfree(spidev);
        }
        mutex_unlock(&device_list_lock);

        return 0;
}

static const struct file_operations spidev_fops = {
        .owner =        THIS_MODULE,
        /* REVISIT switch to aio primitives, so that userspace
         * gets more complete API coverage.  It'll simplify things
         * too, except for the locking.
         */
        .write =        spidev_write,
        .read =         spidev_read,
        .unlocked_ioctl = spidev_ioctl,
        .compat_ioctl = spidev_compat_ioctl,
        .open =         spidev_open,
        .release =      spidev_release,
        .llseek =       no_llseek,
};

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

/* The main reason to have this class is to make mdev/udev create the
 * /dev/spidevB.C character device nodes exposing our userspace API.
 * It also simplifies memory management.
 */

static struct class *spidev_class;

#ifdef CONFIG_OF
static const struct of_device_id spidev_dt_ids[] = {
        { .compatible = "rohm,dh2228fv" },
        { .compatible = "lineartechnology,ltc2488" },
        { .compatible = "ge,achc" },
        { .compatible = "semtech,sx1301" },
        {},
};
MODULE_DEVICE_TABLE(of, spidev_dt_ids);
#endif

#ifdef CONFIG_ACPI

/* Dummy SPI devices not to be used in production systems */
#define SPIDEV_ACPI_DUMMY       1

static const struct acpi_device_id spidev_acpi_ids[] = {
        /*
         * The ACPI SPT000* devices are only meant for development and
         * testing. Systems used in production should have a proper ACPI
         * description of the connected peripheral and they should also use
         * a proper driver instead of poking directly to the SPI bus.
         */
        { "SPT0001", SPIDEV_ACPI_DUMMY },
        { "SPT0002", SPIDEV_ACPI_DUMMY },
        { "SPT0003", SPIDEV_ACPI_DUMMY },
        {},
};
MODULE_DEVICE_TABLE(acpi, spidev_acpi_ids);

static void spidev_probe_acpi(struct spi_device *spi)
{
        const struct acpi_device_id *id;

        if (!has_acpi_companion(&spi->dev))
                return;

        id = acpi_match_device(spidev_acpi_ids, &spi->dev);
        if (WARN_ON(!id))
                return;

        if (id->driver_data == SPIDEV_ACPI_DUMMY)
                dev_warn(&spi->dev, "do not use this driver in production systems!\n");
}
#else
static inline void spidev_probe_acpi(struct spi_device *spi) {}
#endif

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

static int spidev_probe(struct spi_device *spi)
{
        struct spidev_data      *spidev;
        int                     status;
        unsigned long           minor;

        /*
         * spidev should never be referenced in DT without a specific
         * compatible string, it is a Linux implementation thing
         * rather than a description of the hardware.
         */
        if (spi->dev.of_node && !of_match_device(spidev_dt_ids, &spi->dev)) {
                dev_err(&spi->dev, "buggy DT: spidev listed directly in DT\n");
                WARN_ON(spi->dev.of_node &&
                        !of_match_device(spidev_dt_ids, &spi->dev));
        }

        spidev_probe_acpi(spi);

        /* Allocate driver data */
        spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);
        if (!spidev)
                return -ENOMEM;

        /* Initialize the driver data */
        spidev->spi = spi;
        spin_lock_init(&spidev->spi_lock);
        mutex_init(&spidev->buf_lock);

        INIT_LIST_HEAD(&spidev->device_entry);

        /* If we can allocate a minor number, hook up this device.
         * Reusing minors is fine so long as udev or mdev is working.
         */
        mutex_lock(&device_list_lock);
        minor = find_first_zero_bit(minors, N_SPI_MINORS);
        if (minor < N_SPI_MINORS) {
                struct device *dev;

                spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
                dev = device_create(spidev_class, &spi->dev, spidev->devt,
                                    spidev, "spidev%d.%d",
                                    spi->master->bus_num, spi->chip_select);
                status = PTR_ERR_OR_ZERO(dev);
        } else {
                dev_dbg(&spi->dev, "no minor number available!\n");
                status = -ENODEV;
        }
        if (status == 0) {
                set_bit(minor, minors);
                list_add(&spidev->device_entry, &device_list);
        }
        mutex_unlock(&device_list_lock);

        spidev->speed_hz = spi->max_speed_hz;

        if (status == 0)
                spi_set_drvdata(spi, spidev);
        else
                kfree(spidev);

        return status;
}

static int spidev_remove(struct spi_device *spi)
{
        struct spidev_data      *spidev = spi_get_drvdata(spi);

        /* make sure ops on existing fds can abort cleanly */
        spin_lock_irq(&spidev->spi_lock);
        spidev->spi = NULL;
        spin_unlock_irq(&spidev->spi_lock);

        /* prevent new opens */
        mutex_lock(&device_list_lock);
        list_del(&spidev->device_entry);
        device_destroy(spidev_class, spidev->devt);
        clear_bit(MINOR(spidev->devt), minors);
        if (spidev->users == 0)
                kfree(spidev);
        mutex_unlock(&device_list_lock);

        return 0;
}

static struct spi_driver spidev_spi_driver = {
        .driver = {
                .name =         "spidev",
                .of_match_table = of_match_ptr(spidev_dt_ids),
                .acpi_match_table = ACPI_PTR(spidev_acpi_ids),
        },
        .probe =        spidev_probe,
        .remove =       spidev_remove,

        /* NOTE:  suspend/resume methods are not necessary here.
         * We don't do anything except pass the requests to/from
         * the underlying controller.  The refrigerator handles
         * most issues; the controller driver handles the rest.
         */
};

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

static int __init spidev_init(void)
{
        int status;

        /* Claim our 256 reserved device numbers.  Then register a class
         * that will key udev/mdev to add/remove /dev nodes.  Last, register
         * the driver which manages those device numbers.
         */
        BUILD_BUG_ON(N_SPI_MINORS > 256);
        status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
        if (status < 0)
                return status;

        spidev_class = class_create(THIS_MODULE, "spidev");
        if (IS_ERR(spidev_class)) {
                unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
                return PTR_ERR(spidev_class);
        }

        status = spi_register_driver(&spidev_spi_driver);
        if (status < 0) {
                class_destroy(spidev_class);
                unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
        }
        return status;
}
module_init(spidev_init);

static void __exit spidev_exit(void)
{
        spi_unregister_driver(&spidev_spi_driver);
        class_destroy(spidev_class);
        unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
}
module_exit(spidev_exit);

MODULE_AUTHOR("Andrea Paterniani, <a.paterniani@swapp-eng.it>");
MODULE_DESCRIPTION("User mode SPI device interface");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:spidev");