Linux 3.3-rc6

[linux/fpc-iii.git] / drivers / pci / msi.c

/*
 * File:        msi.c
 * Purpose:     PCI Message Signaled Interrupt (MSI)
 *
 * Copyright (C) 2003-2004 Intel
 * Copyright (C) Tom Long Nguyen (tom.l.nguyen@intel.com)
 */

#include <linux/err.h>
#include <linux/mm.h>
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/ioport.h>
#include <linux/pci.h>
#include <linux/proc_fs.h>
#include <linux/msi.h>
#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/io.h>
#include <linux/slab.h>

#include "pci.h"
#include "msi.h"

static int pci_msi_enable = 1;

/* Arch hooks */

#ifndef arch_msi_check_device
int arch_msi_check_device(struct pci_dev *dev, int nvec, int type)
{
        return 0;
}
#endif

#ifndef arch_setup_msi_irqs
# define arch_setup_msi_irqs default_setup_msi_irqs
# define HAVE_DEFAULT_MSI_SETUP_IRQS
#endif

#ifdef HAVE_DEFAULT_MSI_SETUP_IRQS
int default_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
{
        struct msi_desc *entry;
        int ret;

        /*
         * If an architecture wants to support multiple MSI, it needs to
         * override arch_setup_msi_irqs()
         */
        if (type == PCI_CAP_ID_MSI && nvec > 1)
                return 1;

        list_for_each_entry(entry, &dev->msi_list, list) {
                ret = arch_setup_msi_irq(dev, entry);
                if (ret < 0)
                        return ret;
                if (ret > 0)
                        return -ENOSPC;
        }

        return 0;
}
#endif

#ifndef arch_teardown_msi_irqs
# define arch_teardown_msi_irqs default_teardown_msi_irqs
# define HAVE_DEFAULT_MSI_TEARDOWN_IRQS
#endif

#ifdef HAVE_DEFAULT_MSI_TEARDOWN_IRQS
void default_teardown_msi_irqs(struct pci_dev *dev)
{
        struct msi_desc *entry;

        list_for_each_entry(entry, &dev->msi_list, list) {
                int i, nvec;
                if (entry->irq == 0)
                        continue;
                nvec = 1 << entry->msi_attrib.multiple;
                for (i = 0; i < nvec; i++)
                        arch_teardown_msi_irq(entry->irq + i);
        }
}
#endif

#ifndef arch_restore_msi_irqs
# define arch_restore_msi_irqs default_restore_msi_irqs
# define HAVE_DEFAULT_MSI_RESTORE_IRQS
#endif

#ifdef HAVE_DEFAULT_MSI_RESTORE_IRQS
void default_restore_msi_irqs(struct pci_dev *dev, int irq)
{
        struct msi_desc *entry;

        entry = NULL;
        if (dev->msix_enabled) {
                list_for_each_entry(entry, &dev->msi_list, list) {
                        if (irq == entry->irq)
                                break;
                }
        } else if (dev->msi_enabled)  {
                entry = irq_get_msi_desc(irq);
        }

        if (entry)
                write_msi_msg(irq, &entry->msg);
}
#endif

static void msi_set_enable(struct pci_dev *dev, int pos, int enable)
{
        u16 control;

        BUG_ON(!pos);

        pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &control);
        control &= ~PCI_MSI_FLAGS_ENABLE;
        if (enable)
                control |= PCI_MSI_FLAGS_ENABLE;
        pci_write_config_word(dev, pos + PCI_MSI_FLAGS, control);
}

static void msix_set_enable(struct pci_dev *dev, int enable)
{
        int pos;
        u16 control;

        pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
        if (pos) {
                pci_read_config_word(dev, pos + PCI_MSIX_FLAGS, &control);
                control &= ~PCI_MSIX_FLAGS_ENABLE;
                if (enable)
                        control |= PCI_MSIX_FLAGS_ENABLE;
                pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);
        }
}

static inline __attribute_const__ u32 msi_mask(unsigned x)
{
        /* Don't shift by >= width of type */
        if (x >= 5)
                return 0xffffffff;
        return (1 << (1 << x)) - 1;
}

static inline __attribute_const__ u32 msi_capable_mask(u16 control)
{
        return msi_mask((control >> 1) & 7);
}

static inline __attribute_const__ u32 msi_enabled_mask(u16 control)
{
        return msi_mask((control >> 4) & 7);
}

/*
 * PCI 2.3 does not specify mask bits for each MSI interrupt.  Attempting to
 * mask all MSI interrupts by clearing the MSI enable bit does not work
 * reliably as devices without an INTx disable bit will then generate a
 * level IRQ which will never be cleared.
 */
static u32 __msi_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
{
        u32 mask_bits = desc->masked;

        if (!desc->msi_attrib.maskbit)
                return 0;

        mask_bits &= ~mask;
        mask_bits |= flag;
        pci_write_config_dword(desc->dev, desc->mask_pos, mask_bits);

        return mask_bits;
}

static void msi_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
{
        desc->masked = __msi_mask_irq(desc, mask, flag);
}

/*
 * This internal function does not flush PCI writes to the device.
 * All users must ensure that they read from the device before either
 * assuming that the device state is up to date, or returning out of this
 * file.  This saves a few milliseconds when initialising devices with lots
 * of MSI-X interrupts.
 */
static u32 __msix_mask_irq(struct msi_desc *desc, u32 flag)
{
        u32 mask_bits = desc->masked;
        unsigned offset = desc->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
                                                PCI_MSIX_ENTRY_VECTOR_CTRL;
        mask_bits &= ~PCI_MSIX_ENTRY_CTRL_MASKBIT;
        if (flag)
                mask_bits |= PCI_MSIX_ENTRY_CTRL_MASKBIT;
        writel(mask_bits, desc->mask_base + offset);

        return mask_bits;
}

static void msix_mask_irq(struct msi_desc *desc, u32 flag)
{
        desc->masked = __msix_mask_irq(desc, flag);
}

static void msi_set_mask_bit(struct irq_data *data, u32 flag)
{
        struct msi_desc *desc = irq_data_get_msi(data);

        if (desc->msi_attrib.is_msix) {
                msix_mask_irq(desc, flag);
                readl(desc->mask_base);         /* Flush write to device */
        } else {
                unsigned offset = data->irq - desc->dev->irq;
                msi_mask_irq(desc, 1 << offset, flag << offset);
        }
}

void mask_msi_irq(struct irq_data *data)
{
        msi_set_mask_bit(data, 1);
}

void unmask_msi_irq(struct irq_data *data)
{
        msi_set_mask_bit(data, 0);
}

void __read_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
{
        BUG_ON(entry->dev->current_state != PCI_D0);

        if (entry->msi_attrib.is_msix) {
                void __iomem *base = entry->mask_base +
                        entry->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE;

                msg->address_lo = readl(base + PCI_MSIX_ENTRY_LOWER_ADDR);
                msg->address_hi = readl(base + PCI_MSIX_ENTRY_UPPER_ADDR);
                msg->data = readl(base + PCI_MSIX_ENTRY_DATA);
        } else {
                struct pci_dev *dev = entry->dev;
                int pos = entry->msi_attrib.pos;
                u16 data;

                pci_read_config_dword(dev, msi_lower_address_reg(pos),
                                        &msg->address_lo);
                if (entry->msi_attrib.is_64) {
                        pci_read_config_dword(dev, msi_upper_address_reg(pos),
                                                &msg->address_hi);
                        pci_read_config_word(dev, msi_data_reg(pos, 1), &data);
                } else {
                        msg->address_hi = 0;
                        pci_read_config_word(dev, msi_data_reg(pos, 0), &data);
                }
                msg->data = data;
        }
}

void read_msi_msg(unsigned int irq, struct msi_msg *msg)
{
        struct msi_desc *entry = irq_get_msi_desc(irq);

        __read_msi_msg(entry, msg);
}

void __get_cached_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
{
        /* Assert that the cache is valid, assuming that
         * valid messages are not all-zeroes. */
        BUG_ON(!(entry->msg.address_hi | entry->msg.address_lo |
                 entry->msg.data));

        *msg = entry->msg;
}

void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg)
{
        struct msi_desc *entry = irq_get_msi_desc(irq);

        __get_cached_msi_msg(entry, msg);
}

void __write_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
{
        if (entry->dev->current_state != PCI_D0) {
                /* Don't touch the hardware now */
        } else if (entry->msi_attrib.is_msix) {
                void __iomem *base;
                base = entry->mask_base +
                        entry->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE;

                writel(msg->address_lo, base + PCI_MSIX_ENTRY_LOWER_ADDR);
                writel(msg->address_hi, base + PCI_MSIX_ENTRY_UPPER_ADDR);
                writel(msg->data, base + PCI_MSIX_ENTRY_DATA);
        } else {
                struct pci_dev *dev = entry->dev;
                int pos = entry->msi_attrib.pos;
                u16 msgctl;

                pci_read_config_word(dev, msi_control_reg(pos), &msgctl);
                msgctl &= ~PCI_MSI_FLAGS_QSIZE;
                msgctl |= entry->msi_attrib.multiple << 4;
                pci_write_config_word(dev, msi_control_reg(pos), msgctl);

                pci_write_config_dword(dev, msi_lower_address_reg(pos),
                                        msg->address_lo);
                if (entry->msi_attrib.is_64) {
                        pci_write_config_dword(dev, msi_upper_address_reg(pos),
                                                msg->address_hi);
                        pci_write_config_word(dev, msi_data_reg(pos, 1),
                                                msg->data);
                } else {
                        pci_write_config_word(dev, msi_data_reg(pos, 0),
                                                msg->data);
                }
        }
        entry->msg = *msg;
}

void write_msi_msg(unsigned int irq, struct msi_msg *msg)
{
        struct msi_desc *entry = irq_get_msi_desc(irq);

        __write_msi_msg(entry, msg);
}

static void free_msi_irqs(struct pci_dev *dev)
{
        struct msi_desc *entry, *tmp;

        list_for_each_entry(entry, &dev->msi_list, list) {
                int i, nvec;
                if (!entry->irq)
                        continue;
                nvec = 1 << entry->msi_attrib.multiple;
                for (i = 0; i < nvec; i++)
                        BUG_ON(irq_has_action(entry->irq + i));
        }

        arch_teardown_msi_irqs(dev);

        list_for_each_entry_safe(entry, tmp, &dev->msi_list, list) {
                if (entry->msi_attrib.is_msix) {
                        if (list_is_last(&entry->list, &dev->msi_list))
                                iounmap(entry->mask_base);
                }

                /*
                 * Its possible that we get into this path
                 * When populate_msi_sysfs fails, which means the entries
                 * were not registered with sysfs.  In that case don't
                 * unregister them.
                 */
                if (entry->kobj.parent) {
                        kobject_del(&entry->kobj);
                        kobject_put(&entry->kobj);
                }

                list_del(&entry->list);
                kfree(entry);
        }
}

static struct msi_desc *alloc_msi_entry(struct pci_dev *dev)
{
        struct msi_desc *desc = kzalloc(sizeof(*desc), GFP_KERNEL);
        if (!desc)
                return NULL;

        INIT_LIST_HEAD(&desc->list);
        desc->dev = dev;

        return desc;
}

static void pci_intx_for_msi(struct pci_dev *dev, int enable)
{
        if (!(dev->dev_flags & PCI_DEV_FLAGS_MSI_INTX_DISABLE_BUG))
                pci_intx(dev, enable);
}

static void __pci_restore_msi_state(struct pci_dev *dev)
{
        int pos;
        u16 control;
        struct msi_desc *entry;

        if (!dev->msi_enabled)
                return;

        entry = irq_get_msi_desc(dev->irq);
        pos = entry->msi_attrib.pos;

        pci_intx_for_msi(dev, 0);
        msi_set_enable(dev, pos, 0);
        arch_restore_msi_irqs(dev, dev->irq);

        pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &control);
        msi_mask_irq(entry, msi_capable_mask(control), entry->masked);
        control &= ~PCI_MSI_FLAGS_QSIZE;
        control |= (entry->msi_attrib.multiple << 4) | PCI_MSI_FLAGS_ENABLE;
        pci_write_config_word(dev, pos + PCI_MSI_FLAGS, control);
}

static void __pci_restore_msix_state(struct pci_dev *dev)
{
        int pos;
        struct msi_desc *entry;
        u16 control;

        if (!dev->msix_enabled)
                return;
        BUG_ON(list_empty(&dev->msi_list));
        entry = list_first_entry(&dev->msi_list, struct msi_desc, list);
        pos = entry->msi_attrib.pos;
        pci_read_config_word(dev, pos + PCI_MSIX_FLAGS, &control);

        /* route the table */
        pci_intx_for_msi(dev, 0);
        control |= PCI_MSIX_FLAGS_ENABLE | PCI_MSIX_FLAGS_MASKALL;
        pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);

        list_for_each_entry(entry, &dev->msi_list, list) {
                arch_restore_msi_irqs(dev, entry->irq);
                msix_mask_irq(entry, entry->masked);
        }

        control &= ~PCI_MSIX_FLAGS_MASKALL;
        pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);
}

void pci_restore_msi_state(struct pci_dev *dev)
{
        __pci_restore_msi_state(dev);
        __pci_restore_msix_state(dev);
}
EXPORT_SYMBOL_GPL(pci_restore_msi_state);


#define to_msi_attr(obj) container_of(obj, struct msi_attribute, attr)
#define to_msi_desc(obj) container_of(obj, struct msi_desc, kobj)

struct msi_attribute {
        struct attribute        attr;
        ssize_t (*show)(struct msi_desc *entry, struct msi_attribute *attr,
                        char *buf);
        ssize_t (*store)(struct msi_desc *entry, struct msi_attribute *attr,
                         const char *buf, size_t count);
};

static ssize_t show_msi_mode(struct msi_desc *entry, struct msi_attribute *atr,
                             char *buf)
{
        return sprintf(buf, "%s\n", entry->msi_attrib.is_msix ? "msix" : "msi");
}

static ssize_t msi_irq_attr_show(struct kobject *kobj,
                                 struct attribute *attr, char *buf)
{
        struct msi_attribute *attribute = to_msi_attr(attr);
        struct msi_desc *entry = to_msi_desc(kobj);

        if (!attribute->show)
                return -EIO;

        return attribute->show(entry, attribute, buf);
}

static const struct sysfs_ops msi_irq_sysfs_ops = {
        .show = msi_irq_attr_show,
};

static struct msi_attribute mode_attribute =
        __ATTR(mode, S_IRUGO, show_msi_mode, NULL);


struct attribute *msi_irq_default_attrs[] = {
        &mode_attribute.attr,
        NULL
};

void msi_kobj_release(struct kobject *kobj)
{
        struct msi_desc *entry = to_msi_desc(kobj);

        pci_dev_put(entry->dev);
}

static struct kobj_type msi_irq_ktype = {
        .release = msi_kobj_release,
        .sysfs_ops = &msi_irq_sysfs_ops,
        .default_attrs = msi_irq_default_attrs,
};

static int populate_msi_sysfs(struct pci_dev *pdev)
{
        struct msi_desc *entry;
        struct kobject *kobj;
        int ret;
        int count = 0;

        pdev->msi_kset = kset_create_and_add("msi_irqs", NULL, &pdev->dev.kobj);
        if (!pdev->msi_kset)
                return -ENOMEM;

        list_for_each_entry(entry, &pdev->msi_list, list) {
                kobj = &entry->kobj;
                kobj->kset = pdev->msi_kset;
                pci_dev_get(pdev);
                ret = kobject_init_and_add(kobj, &msi_irq_ktype, NULL,
                                     "%u", entry->irq);
                if (ret)
                        goto out_unroll;

                count++;
        }

        return 0;

out_unroll:
        list_for_each_entry(entry, &pdev->msi_list, list) {
                if (!count)
                        break;
                kobject_del(&entry->kobj);
                kobject_put(&entry->kobj);
                count--;
        }
        return ret;
}

/**
 * msi_capability_init - configure device's MSI capability structure
 * @dev: pointer to the pci_dev data structure of MSI device function
 * @nvec: number of interrupts to allocate
 *
 * Setup the MSI capability structure of the device with the requested
 * number of interrupts.  A return value of zero indicates the successful
 * setup of an entry with the new MSI irq.  A negative return value indicates
 * an error, and a positive return value indicates the number of interrupts
 * which could have been allocated.
 */
static int msi_capability_init(struct pci_dev *dev, int nvec)
{
        struct msi_desc *entry;
        int pos, ret;
        u16 control;
        unsigned mask;

        pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
        msi_set_enable(dev, pos, 0);    /* Disable MSI during set up */

        pci_read_config_word(dev, msi_control_reg(pos), &control);
        /* MSI Entry Initialization */
        entry = alloc_msi_entry(dev);
        if (!entry)
                return -ENOMEM;

        entry->msi_attrib.is_msix       = 0;
        entry->msi_attrib.is_64         = is_64bit_address(control);
        entry->msi_attrib.entry_nr      = 0;
        entry->msi_attrib.maskbit       = is_mask_bit_support(control);
        entry->msi_attrib.default_irq   = dev->irq;     /* Save IOAPIC IRQ */
        entry->msi_attrib.pos           = pos;

        entry->mask_pos = msi_mask_reg(pos, entry->msi_attrib.is_64);
        /* All MSIs are unmasked by default, Mask them all */
        if (entry->msi_attrib.maskbit)
                pci_read_config_dword(dev, entry->mask_pos, &entry->masked);
        mask = msi_capable_mask(control);
        msi_mask_irq(entry, mask, mask);

        list_add_tail(&entry->list, &dev->msi_list);

        /* Configure MSI capability structure */
        ret = arch_setup_msi_irqs(dev, nvec, PCI_CAP_ID_MSI);
        if (ret) {
                msi_mask_irq(entry, mask, ~mask);
                free_msi_irqs(dev);
                return ret;
        }

        ret = populate_msi_sysfs(dev);
        if (ret) {
                msi_mask_irq(entry, mask, ~mask);
                free_msi_irqs(dev);
                return ret;
        }

        /* Set MSI enabled bits  */
        pci_intx_for_msi(dev, 0);
        msi_set_enable(dev, pos, 1);
        dev->msi_enabled = 1;

        dev->irq = entry->irq;
        return 0;
}

static void __iomem *msix_map_region(struct pci_dev *dev, unsigned pos,
                                                        unsigned nr_entries)
{
        resource_size_t phys_addr;
        u32 table_offset;
        u8 bir;

        pci_read_config_dword(dev, msix_table_offset_reg(pos), &table_offset);
        bir = (u8)(table_offset & PCI_MSIX_FLAGS_BIRMASK);
        table_offset &= ~PCI_MSIX_FLAGS_BIRMASK;
        phys_addr = pci_resource_start(dev, bir) + table_offset;

        return ioremap_nocache(phys_addr, nr_entries * PCI_MSIX_ENTRY_SIZE);
}

static int msix_setup_entries(struct pci_dev *dev, unsigned pos,
                                void __iomem *base, struct msix_entry *entries,
                                int nvec)
{
        struct msi_desc *entry;
        int i;

        for (i = 0; i < nvec; i++) {
                entry = alloc_msi_entry(dev);
                if (!entry) {
                        if (!i)
                                iounmap(base);
                        else
                                free_msi_irqs(dev);
                        /* No enough memory. Don't try again */
                        return -ENOMEM;
                }

                entry->msi_attrib.is_msix       = 1;
                entry->msi_attrib.is_64         = 1;
                entry->msi_attrib.entry_nr      = entries[i].entry;
                entry->msi_attrib.default_irq   = dev->irq;
                entry->msi_attrib.pos           = pos;
                entry->mask_base                = base;

                list_add_tail(&entry->list, &dev->msi_list);
        }

        return 0;
}

static void msix_program_entries(struct pci_dev *dev,
                                        struct msix_entry *entries)
{
        struct msi_desc *entry;
        int i = 0;

        list_for_each_entry(entry, &dev->msi_list, list) {
                int offset = entries[i].entry * PCI_MSIX_ENTRY_SIZE +
                                                PCI_MSIX_ENTRY_VECTOR_CTRL;

                entries[i].vector = entry->irq;
                irq_set_msi_desc(entry->irq, entry);
                entry->masked = readl(entry->mask_base + offset);
                msix_mask_irq(entry, 1);
                i++;
        }
}

/**
 * msix_capability_init - configure device's MSI-X capability
 * @dev: pointer to the pci_dev data structure of MSI-X device function
 * @entries: pointer to an array of struct msix_entry entries
 * @nvec: number of @entries
 *
 * Setup the MSI-X capability structure of device function with a
 * single MSI-X irq. A return of zero indicates the successful setup of
 * requested MSI-X entries with allocated irqs or non-zero for otherwise.
 **/
static int msix_capability_init(struct pci_dev *dev,
                                struct msix_entry *entries, int nvec)
{
        int pos, ret;
        u16 control;
        void __iomem *base;

        pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
        pci_read_config_word(dev, pos + PCI_MSIX_FLAGS, &control);

        /* Ensure MSI-X is disabled while it is set up */
        control &= ~PCI_MSIX_FLAGS_ENABLE;
        pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);

        /* Request & Map MSI-X table region */
        base = msix_map_region(dev, pos, multi_msix_capable(control));
        if (!base)
                return -ENOMEM;

        ret = msix_setup_entries(dev, pos, base, entries, nvec);
        if (ret)
                return ret;

        ret = arch_setup_msi_irqs(dev, nvec, PCI_CAP_ID_MSIX);
        if (ret)
                goto error;

        /*
         * Some devices require MSI-X to be enabled before we can touch the
         * MSI-X registers.  We need to mask all the vectors to prevent
         * interrupts coming in before they're fully set up.
         */
        control |= PCI_MSIX_FLAGS_MASKALL | PCI_MSIX_FLAGS_ENABLE;
        pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);

        msix_program_entries(dev, entries);

        ret = populate_msi_sysfs(dev);
        if (ret) {
                ret = 0;
                goto error;
        }

        /* Set MSI-X enabled bits and unmask the function */
        pci_intx_for_msi(dev, 0);
        dev->msix_enabled = 1;

        control &= ~PCI_MSIX_FLAGS_MASKALL;
        pci_write_config_word(dev, pos + PCI_MSIX_FLAGS, control);

        return 0;

error:
        if (ret < 0) {
                /*
                 * If we had some success, report the number of irqs
                 * we succeeded in setting up.
                 */
                struct msi_desc *entry;
                int avail = 0;

                list_for_each_entry(entry, &dev->msi_list, list) {
                        if (entry->irq != 0)
                                avail++;
                }
                if (avail != 0)
                        ret = avail;
        }

        free_msi_irqs(dev);

        return ret;
}

/**
 * pci_msi_check_device - check whether MSI may be enabled on a device
 * @dev: pointer to the pci_dev data structure of MSI device function
 * @nvec: how many MSIs have been requested ?
 * @type: are we checking for MSI or MSI-X ?
 *
 * Look at global flags, the device itself, and its parent busses
 * to determine if MSI/-X are supported for the device. If MSI/-X is
 * supported return 0, else return an error code.
 **/
static int pci_msi_check_device(struct pci_dev *dev, int nvec, int type)
{
        struct pci_bus *bus;
        int ret;

        /* MSI must be globally enabled and supported by the device */
        if (!pci_msi_enable || !dev || dev->no_msi)
                return -EINVAL;

        /*
         * You can't ask to have 0 or less MSIs configured.
         *  a) it's stupid ..
         *  b) the list manipulation code assumes nvec >= 1.
         */
        if (nvec < 1)
                return -ERANGE;

        /*
         * Any bridge which does NOT route MSI transactions from its
         * secondary bus to its primary bus must set NO_MSI flag on
         * the secondary pci_bus.
         * We expect only arch-specific PCI host bus controller driver
         * or quirks for specific PCI bridges to be setting NO_MSI.
         */
        for (bus = dev->bus; bus; bus = bus->parent)
                if (bus->bus_flags & PCI_BUS_FLAGS_NO_MSI)
                        return -EINVAL;

        ret = arch_msi_check_device(dev, nvec, type);
        if (ret)
                return ret;

        if (!pci_find_capability(dev, type))
                return -EINVAL;

        return 0;
}

/**
 * pci_enable_msi_block - configure device's MSI capability structure
 * @dev: device to configure
 * @nvec: number of interrupts to configure
 *
 * Allocate IRQs for a device with the MSI capability.
 * This function returns a negative errno if an error occurs.  If it
 * is unable to allocate the number of interrupts requested, it returns
 * the number of interrupts it might be able to allocate.  If it successfully
 * allocates at least the number of interrupts requested, it returns 0 and
 * updates the @dev's irq member to the lowest new interrupt number; the
 * other interrupt numbers allocated to this device are consecutive.
 */
int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
{
        int status, pos, maxvec;
        u16 msgctl;

        pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
        if (!pos)
                return -EINVAL;
        pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &msgctl);
        maxvec = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
        if (nvec > maxvec)
                return maxvec;

        status = pci_msi_check_device(dev, nvec, PCI_CAP_ID_MSI);
        if (status)
                return status;

        WARN_ON(!!dev->msi_enabled);

        /* Check whether driver already requested MSI-X irqs */
        if (dev->msix_enabled) {
                dev_info(&dev->dev, "can't enable MSI "
                         "(MSI-X already enabled)\n");
                return -EINVAL;
        }

        status = msi_capability_init(dev, nvec);
        return status;
}
EXPORT_SYMBOL(pci_enable_msi_block);

void pci_msi_shutdown(struct pci_dev *dev)
{
        struct msi_desc *desc;
        u32 mask;
        u16 ctrl;
        unsigned pos;

        if (!pci_msi_enable || !dev || !dev->msi_enabled)
                return;

        BUG_ON(list_empty(&dev->msi_list));
        desc = list_first_entry(&dev->msi_list, struct msi_desc, list);
        pos = desc->msi_attrib.pos;

        msi_set_enable(dev, pos, 0);
        pci_intx_for_msi(dev, 1);
        dev->msi_enabled = 0;

        /* Return the device with MSI unmasked as initial states */
        pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &ctrl);
        mask = msi_capable_mask(ctrl);
        /* Keep cached state to be restored */
        __msi_mask_irq(desc, mask, ~mask);

        /* Restore dev->irq to its default pin-assertion irq */
        dev->irq = desc->msi_attrib.default_irq;
}

void pci_disable_msi(struct pci_dev *dev)
{
        if (!pci_msi_enable || !dev || !dev->msi_enabled)
                return;

        pci_msi_shutdown(dev);
        free_msi_irqs(dev);
        kset_unregister(dev->msi_kset);
        dev->msi_kset = NULL;
}
EXPORT_SYMBOL(pci_disable_msi);

/**
 * pci_msix_table_size - return the number of device's MSI-X table entries
 * @dev: pointer to the pci_dev data structure of MSI-X device function
 */
int pci_msix_table_size(struct pci_dev *dev)
{
        int pos;
        u16 control;

        pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
        if (!pos)
                return 0;

        pci_read_config_word(dev, msi_control_reg(pos), &control);
        return multi_msix_capable(control);
}

/**
 * pci_enable_msix - configure device's MSI-X capability structure
 * @dev: pointer to the pci_dev data structure of MSI-X device function
 * @entries: pointer to an array of MSI-X entries
 * @nvec: number of MSI-X irqs requested for allocation by device driver
 *
 * Setup the MSI-X capability structure of device function with the number
 * of requested irqs upon its software driver call to request for
 * MSI-X mode enabled on its hardware device function. A return of zero
 * indicates the successful configuration of MSI-X capability structure
 * with new allocated MSI-X irqs. A return of < 0 indicates a failure.
 * Or a return of > 0 indicates that driver request is exceeding the number
 * of irqs or MSI-X vectors available. Driver should use the returned value to
 * re-send its request.
 **/
int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec)
{
        int status, nr_entries;
        int i, j;

        if (!entries)
                return -EINVAL;

        status = pci_msi_check_device(dev, nvec, PCI_CAP_ID_MSIX);
        if (status)
                return status;

        nr_entries = pci_msix_table_size(dev);
        if (nvec > nr_entries)
                return nr_entries;

        /* Check for any invalid entries */
        for (i = 0; i < nvec; i++) {
                if (entries[i].entry >= nr_entries)
                        return -EINVAL;         /* invalid entry */
                for (j = i + 1; j < nvec; j++) {
                        if (entries[i].entry == entries[j].entry)
                                return -EINVAL; /* duplicate entry */
                }
        }
        WARN_ON(!!dev->msix_enabled);

        /* Check whether driver already requested for MSI irq */
        if (dev->msi_enabled) {
                dev_info(&dev->dev, "can't enable MSI-X "
                       "(MSI IRQ already assigned)\n");
                return -EINVAL;
        }
        status = msix_capability_init(dev, entries, nvec);
        return status;
}
EXPORT_SYMBOL(pci_enable_msix);

void pci_msix_shutdown(struct pci_dev *dev)
{
        struct msi_desc *entry;

        if (!pci_msi_enable || !dev || !dev->msix_enabled)
                return;

        /* Return the device with MSI-X masked as initial states */
        list_for_each_entry(entry, &dev->msi_list, list) {
                /* Keep cached states to be restored */
                __msix_mask_irq(entry, 1);
        }

        msix_set_enable(dev, 0);
        pci_intx_for_msi(dev, 1);
        dev->msix_enabled = 0;
}

void pci_disable_msix(struct pci_dev *dev)
{
        if (!pci_msi_enable || !dev || !dev->msix_enabled)
                return;

        pci_msix_shutdown(dev);
        free_msi_irqs(dev);
        kset_unregister(dev->msi_kset);
        dev->msi_kset = NULL;
}
EXPORT_SYMBOL(pci_disable_msix);

/**
 * msi_remove_pci_irq_vectors - reclaim MSI(X) irqs to unused state
 * @dev: pointer to the pci_dev data structure of MSI(X) device function
 *
 * Being called during hotplug remove, from which the device function
 * is hot-removed. All previous assigned MSI/MSI-X irqs, if
 * allocated for this device function, are reclaimed to unused state,
 * which may be used later on.
 **/
void msi_remove_pci_irq_vectors(struct pci_dev *dev)
{
        if (!pci_msi_enable || !dev)
                return;

        if (dev->msi_enabled || dev->msix_enabled)
                free_msi_irqs(dev);
}

void pci_no_msi(void)
{
        pci_msi_enable = 0;
}

/**
 * pci_msi_enabled - is MSI enabled?
 *
 * Returns true if MSI has not been disabled by the command-line option
 * pci=nomsi.
 **/
int pci_msi_enabled(void)
{
        return pci_msi_enable;
}
EXPORT_SYMBOL(pci_msi_enabled);

void pci_msi_init_pci_dev(struct pci_dev *dev)
{
        int pos;
        INIT_LIST_HEAD(&dev->msi_list);

        /* Disable the msi hardware to avoid screaming interrupts
         * during boot.  This is the power on reset default so
         * usually this should be a noop.
         */
        pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
        if (pos)
                msi_set_enable(dev, pos, 0);
        msix_set_enable(dev, 0);
}