[PATCH v2 0/3] uio: add MSI/MSI-X support to uio_pci_generic driver

[PATCH v2 0/3] uio: add MSI/MSI-X support to uio_pci_generic driver

[Vlad Zolotarov]

This series add support for MSI and MSI-X interrupts to uio_pci_generic driver.
 
Currently uio_pci_generic supports only legacy INT#x interrupts source. However
there are situations when this is not enough, for instance SR-IOV VF devices that
simply don't have INT#x capability. For such devices uio_pci_generic will simply
fail (more specifically probe() will fail).
 
When IOMMU is either not available (e.g. Amazon EC2) or not acceptable due to performance
overhead and thus VFIO is not an option users that develop user-space drivers are left
without any option but to develop some proprietary UIO drivers (e.g. igb_uio driver in Intel's
DPDK) just to be able to use UIO infrastructure.
 
This series provides a generic solution for this problem while preserving the original behaviour
for devices for which the original uio_pci_generic had worked before (i.e. INT#x will be used by default).

New in v2:
   - Added #include <linux/uaccess.h> to uio_pci_generic.c


Vlad Zolotarov (3):
  uio: add ioctl support
  uio_pci_generic: add MSI/MSI-X support
  Documentation: update uio-howto

 Documentation/DocBook/uio-howto.tmpl |  29 ++-
 drivers/uio/uio.c                    |  15 ++
 drivers/uio/uio_pci_generic.c        | 410 +++++++++++++++++++++++++++++++++--
 include/linux/uio_driver.h           |   3 +
 include/linux/uio_pci_generic.h      |  36 +++
 5 files changed, 467 insertions(+), 26 deletions(-)
 create mode 100644 include/linux/uio_pci_generic.h

-- 
2.1.0

[PATCH v2 1/3] uio: add ioctl support

[Vlad Zolotarov]

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
---
 drivers/uio/uio.c          | 15 +++++++++++++++
 include/linux/uio_driver.h |  3 +++
 2 files changed, 18 insertions(+)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 8196581..714b0e5 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -704,6 +704,20 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 	}
 }
 
+static long uio_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
+{
+	struct uio_listener *listener = filep->private_data;
+	struct uio_device *idev = listener->dev;
+
+	if (!idev->info)
+		return -EIO;
+
+	if (!idev->info->ioctl)
+		return -ENOTTY;
+
+	return idev->info->ioctl(idev->info, cmd, arg);
+}
+
 static const struct file_operations uio_fops = {
 	.owner		= THIS_MODULE,
 	.open		= uio_open,
@@ -712,6 +726,7 @@ static const struct file_operations uio_fops = {
 	.write		= uio_write,
 	.mmap		= uio_mmap,
 	.poll		= uio_poll,
+	.unlocked_ioctl	= uio_ioctl,
 	.fasync		= uio_fasync,
 	.llseek		= noop_llseek,
 };
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 32c0e83..10d7833 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -89,6 +89,7 @@ struct uio_device {
  * @mmap:		mmap operation for this uio device
  * @open:		open operation for this uio device
  * @release:		release operation for this uio device
+ * @ioctl:		ioctl handler
  * @irqcontrol:		disable/enable irqs when 0/1 is written to /dev/uioX
  */
 struct uio_info {
@@ -105,6 +106,8 @@ struct uio_info {
 	int (*open)(struct uio_info *info, struct inode *inode);
 	int (*release)(struct uio_info *info, struct inode *inode);
 	int (*irqcontrol)(struct uio_info *info, s32 irq_on);
+	int (*ioctl)(struct uio_info *info, unsigned int cmd,
+		     unsigned long arg);
 };
 
 extern int __must_check
-- 
2.1.0

[PATCH v2 2/3] uio_pci_generic: add MSI/MSI-X support

[Vlad Zolotarov]

Add support for MSI and MSI-X interrupt modes:
   - Interrupt mode selection order is:
        INT#X (for backward compatibility) -> MSI-X -> MSI.
   - Add ioctl() commands:
      - UIO_PCI_GENERIC_INT_MODE_GET: query the current interrupt mode.
      - UIO_PCI_GENERIC_IRQ_NUM_GET: query the maximum number of IRQs.
      - UIO_PCI_GENERIC_IRQ_SET: bind the IRQ to eventfd (similar to vfio).
   - Add mappings to all bars (memory and portio): some devices have
     registers related to MSI/MSI-X handling outside BAR0.

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
---
New in v2:
   - Added #include <linux/uaccess.h> to uio_pci_generic.c
---
 drivers/uio/uio_pci_generic.c   | 410 +++++++++++++++++++++++++++++++++++++---
 include/linux/uio_pci_generic.h |  36 ++++
 2 files changed, 423 insertions(+), 23 deletions(-)
 create mode 100644 include/linux/uio_pci_generic.h

diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
index d0b508b..90e7b0d 100644
--- a/drivers/uio/uio_pci_generic.c
+++ b/drivers/uio/uio_pci_generic.c
@@ -22,16 +22,32 @@
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/msi.h>
 #include <linux/slab.h>
 #include <linux/uio_driver.h>
+#include <linux/uio_pci_generic.h>
+#include <linux/eventfd.h>
+#include <linux/uaccess.h>
 
 #define DRIVER_VERSION	"0.01.0"
 #define DRIVER_AUTHOR	"Michael S. Tsirkin <mst@redhat.com>"
 #define DRIVER_DESC	"Generic UIO driver for PCI 2.3 devices"
 
+struct msix_info {
+	int num_irqs;
+	struct msix_entry *table;
+	struct uio_msix_irq_ctx {
+		struct eventfd_ctx *trigger;	/* MSI-x vector to eventfd */
+		char *name;			/* name in /proc/interrupts */
+	} *ctx;
+};
+
 struct uio_pci_generic_dev {
 	struct uio_info info;
 	struct pci_dev *pdev;
+	struct mutex msix_state_lock;		/* ioctl mutex */
+	enum uio_int_mode int_mode;
+	struct msix_info msix;
 };
 
 static inline struct uio_pci_generic_dev *
@@ -40,9 +56,177 @@ to_uio_pci_generic_dev(struct uio_info *info)
 	return container_of(info, struct uio_pci_generic_dev, info);
 }
 
-/* Interrupt handler. Read/modify/write the command register to disable
- * the interrupt. */
-static irqreturn_t irqhandler(int irq, struct uio_info *info)
+/* Unmap previously ioremap'd resources */
+static void release_iomaps(struct uio_pci_generic_dev *gdev)
+{
+	int i;
+	struct uio_mem *mem = gdev->info.mem;
+
+	for (i = 0; i < MAX_UIO_MAPS; i++, mem++) {
+		if (mem->internal_addr) {
+			iounmap(mem->internal_addr);
+			mem->internal_addr = NULL;
+		}
+	}
+}
+
+static int setup_maps(struct pci_dev *pdev, struct uio_info *info)
+{
+	int i, m = 0, p = 0, err;
+	static const char * const bar_names[] = {
+		"BAR0",	"BAR1",	"BAR2",	"BAR3",	"BAR4",	"BAR5",
+	};
+
+	for (i = 0; i < ARRAY_SIZE(bar_names); i++) {
+		unsigned long start = pci_resource_start(pdev, i);
+		unsigned long flags = pci_resource_flags(pdev, i);
+		unsigned long len = pci_resource_len(pdev, i);
+
+		if (start == 0 || len == 0)
+			continue;
+
+		if (flags & IORESOURCE_MEM) {
+			void *addr;
+
+			if (m >= MAX_UIO_MAPS)
+				continue;
+
+			addr = ioremap(start, len);
+			if (addr == NULL) {
+				err = -EINVAL;
+				goto fail;
+			}
+
+			info->mem[m].name = bar_names[i];
+			info->mem[m].addr = start;
+			info->mem[m].internal_addr = addr;
+			info->mem[m].size = len;
+			info->mem[m].memtype = UIO_MEM_PHYS;
+			++m;
+		} else if (flags & IORESOURCE_IO) {
+			if (p >= MAX_UIO_PORT_REGIONS)
+				continue;
+
+			info->port[p].name = bar_names[i];
+			info->port[p].start = start;
+			info->port[p].size = len;
+			info->port[p].porttype = UIO_PORT_X86;
+			++p;
+		}
+	}
+
+	return 0;
+fail:
+	for (i = 0; i < m; i++) {
+		iounmap(info->mem[i].internal_addr);
+		info->mem[i].internal_addr = NULL;
+	}
+
+	return err;
+}
+
+static irqreturn_t msix_irqhandler(int irq, void *arg);
+
+/* set the mapping between vector # and existing eventfd. */
+static int set_irq_eventfd(struct uio_pci_generic_dev *gdev, int vec, int fd)
+{
+	struct uio_msix_irq_ctx *ctx;
+	struct eventfd_ctx *trigger;
+	struct pci_dev *pdev = gdev->pdev;
+	int irq, err;
+
+	if (vec >= gdev->msix.num_irqs) {
+		dev_notice(&gdev->pdev->dev, "vec %u >= num_vec %u\n",
+			   vec, gdev->msix.num_irqs);
+		return -ERANGE;
+	}
+
+	irq = gdev->msix.table[vec].vector;
+
+	/* Cleanup existing irq mapping */
+	ctx = &gdev->msix.ctx[vec];
+	if (ctx->trigger) {
+		free_irq(irq, ctx->trigger);
+		eventfd_ctx_put(ctx->trigger);
+		ctx->trigger = NULL;
+	}
+
+	/* Passing -1 is used to disable interrupt */
+	if (fd < 0)
+		return 0;
+
+
+	trigger = eventfd_ctx_fdget(fd);
+	if (IS_ERR(trigger)) {
+		err = PTR_ERR(trigger);
+		dev_notice(&gdev->pdev->dev,
+			   "eventfd ctx get failed: %d\n", err);
+		return err;
+	}
+
+	err = request_irq(irq, msix_irqhandler, 0, ctx->name, trigger);
+	if (err) {
+		dev_notice(&pdev->dev, "request irq failed: %d\n", err);
+		eventfd_ctx_put(trigger);
+		return err;
+	}
+
+	dev_dbg(&pdev->dev, "map vector %u to fd %d trigger %p\n",
+		vec, fd, trigger);
+	ctx->trigger = trigger;
+
+	return 0;
+}
+
+static int uio_pci_generic_ioctl(struct uio_info *info, unsigned int cmd,
+				 unsigned long arg)
+{
+	struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
+	struct uio_pci_generic_irq_set hdr;
+	int err;
+
+	switch (cmd) {
+	case UIO_PCI_GENERIC_IRQ_SET:
+		if (copy_from_user(&hdr, (void __user *)arg, sizeof(hdr)))
+			return -EFAULT;
+
+		/* Locking is needed to ensure two things:
+		 *  1) Two IRQ_SET ioctl()'s are not running in parallel.
+		 *  2) IRQ_SET ioctl() is not running in parallel with remove().
+		 */
+		mutex_lock(&gdev->msix_state_lock);
+		if (gdev->int_mode != UIO_INT_MODE_MSIX) {
+			mutex_unlock(&gdev->msix_state_lock);
+			return -EOPNOTSUPP;
+		}
+
+		err = set_irq_eventfd(gdev, hdr.vec, hdr.fd);
+		mutex_unlock(&gdev->msix_state_lock);
+
+		break;
+	case UIO_PCI_GENERIC_IRQ_NUM_GET:
+		if (gdev->int_mode == UIO_INT_MODE_NONE)
+			err = put_user(0, (u32 __user *)arg);
+		else if (gdev->int_mode != UIO_INT_MODE_MSIX)
+			err = put_user(1, (u32 __user *)arg);
+		else
+			err = put_user(gdev->msix.num_irqs,
+				       (u32 __user *)arg);
+
+		break;
+	case UIO_PCI_GENERIC_INT_MODE_GET:
+		err = put_user(gdev->int_mode, (u32 __user *)arg);
+
+		break;
+	default:
+		err = -EOPNOTSUPP;
+	}
+
+	return err;
+}
+
+/* INT#X interrupt handler. */
+static irqreturn_t intx_irqhandler(int irq, struct uio_info *info)
 {
 	struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
 
@@ -53,8 +237,162 @@ static irqreturn_t irqhandler(int irq, struct uio_info *info)
 	return IRQ_HANDLED;
 }
 
-static int probe(struct pci_dev *pdev,
-			   const struct pci_device_id *id)
+/* MSI interrupt handler. */
+static irqreturn_t msi_irqhandler(int irq, struct uio_info *info)
+{
+	/* UIO core will signal the user process. */
+	return IRQ_HANDLED;
+}
+
+/* MSI-X interrupt handler. */
+static irqreturn_t msix_irqhandler(int irq, void *arg)
+{
+	struct eventfd_ctx *trigger = arg;
+
+	pr_devel("irq %u trigger %p\n", irq, trigger);
+
+	eventfd_signal(trigger, 1);
+	return IRQ_HANDLED;
+}
+
+static bool enable_intx(struct uio_pci_generic_dev *gdev)
+{
+	struct pci_dev *pdev = gdev->pdev;
+
+	if (!pdev->irq || !pci_intx_mask_supported(pdev))
+		return false;
+
+	gdev->int_mode = UIO_INT_MODE_INTX;
+	gdev->info.irq = pdev->irq;
+	gdev->info.irq_flags = IRQF_SHARED;
+	gdev->info.handler = intx_irqhandler;
+
+	return true;
+}
+
+static void set_pci_master(struct pci_dev *pdev)
+{
+	pci_set_master(pdev);
+	dev_warn(&pdev->dev, "Enabling PCI bus mastering. Bogus userspace application is able to trash kernel memory using DMA");
+	add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+}
+
+static bool enable_msi(struct uio_pci_generic_dev *gdev)
+{
+	struct pci_dev *pdev = gdev->pdev;
+
+	set_pci_master(pdev);
+
+	if (pci_enable_msi(pdev))
+		return false;
+
+	gdev->int_mode = UIO_INT_MODE_MSI;
+	gdev->info.irq = pdev->irq;
+	gdev->info.irq_flags = 0;
+	gdev->info.handler = msi_irqhandler;
+
+	return true;
+}
+
+static bool enable_msix(struct uio_pci_generic_dev *gdev)
+{
+	struct pci_dev *pdev = gdev->pdev;
+	int i, vectors = pci_msix_vec_count(pdev);
+
+	if (vectors <= 0)
+		return false;
+
+	gdev->msix.table = kcalloc(vectors, sizeof(struct msix_entry),
+				   GFP_KERNEL);
+	if (!gdev->msix.table) {
+		dev_err(&pdev->dev, "Failed to allocate memory for MSI-X table");
+		return false;
+	}
+
+	gdev->msix.ctx = kcalloc(vectors, sizeof(struct uio_msix_irq_ctx),
+				 GFP_KERNEL);
+	if (!gdev->msix.ctx) {
+		dev_err(&pdev->dev, "Failed to allocate memory for MSI-X contexts");
+		goto err_ctx_alloc;
+	}
+
+	for (i = 0; i < vectors; i++) {
+		gdev->msix.table[i].entry = i;
+		gdev->msix.ctx[i].name = kasprintf(GFP_KERNEL,
+						   KBUILD_MODNAME "[%d](%s)",
+						   i, pci_name(pdev));
+		if (!gdev->msix.ctx[i].name)
+			goto err_name_alloc;
+	}
+
+	set_pci_master(pdev);
+
+	if (pci_enable_msix(pdev, gdev->msix.table, vectors))
+		goto err_msix_enable;
+
+	gdev->int_mode = UIO_INT_MODE_MSIX;
+	gdev->info.irq = UIO_IRQ_CUSTOM;
+	gdev->msix.num_irqs = vectors;
+
+	return true;
+
+err_msix_enable:
+	pci_clear_master(pdev);
+err_name_alloc:
+	for (i = 0; i < vectors; i++)
+		kfree(gdev->msix.ctx[i].name);
+
+	kfree(gdev->msix.ctx);
+err_ctx_alloc:
+	kfree(gdev->msix.table);
+
+	return false;
+}
+
+/**
+ * Disable interrupts and free related resources.
+ *
+ * @gdev device handle
+ *
+ * This function should be called after the corresponding UIO device has been
+ * unregistered. This will ensure that there are no currently running ioctl()s
+ * and there won't be any new ones until next probe() call.
+ */
+static void disable_intr(struct uio_pci_generic_dev *gdev)
+{
+	struct pci_dev *pdev = gdev->pdev;
+	int i;
+
+	switch (gdev->int_mode) {
+	case UIO_INT_MODE_MSI:
+		pci_disable_msi(pdev);
+		pci_clear_master(pdev);
+
+		break;
+	case UIO_INT_MODE_MSIX:
+		/* No need for locking here since there shouldn't be any
+		 * ioctl()s running by now.
+		 */
+		for (i = 0; i < gdev->msix.num_irqs; i++) {
+			if (gdev->msix.ctx[i].trigger)
+				set_irq_eventfd(gdev, i, -1);
+
+			kfree(gdev->msix.ctx[i].name);
+		}
+
+		pci_disable_msix(pdev);
+		pci_clear_master(pdev);
+		kfree(gdev->msix.ctx);
+		kfree(gdev->msix.table);
+
+		break;
+	default:
+		break;
+	}
+}
+
+
+static int probe(struct pci_dev *pdev, const struct pci_device_id *id)
 {
 	struct uio_pci_generic_dev *gdev;
 	int err;
@@ -66,42 +404,64 @@ static int probe(struct pci_dev *pdev,
 		return err;
 	}
 
-	if (!pdev->irq) {
-		dev_warn(&pdev->dev, "No IRQ assigned to device: "
-			 "no support for interrupts?\n");
-		pci_disable_device(pdev);
-		return -ENODEV;
-	}
-
-	if (!pci_intx_mask_supported(pdev)) {
-		err = -ENODEV;
-		goto err_verify;
-	}
-
 	gdev = kzalloc(sizeof(struct uio_pci_generic_dev), GFP_KERNEL);
 	if (!gdev) {
 		err = -ENOMEM;
 		goto err_alloc;
 	}
 
+	gdev->pdev = pdev;
 	gdev->info.name = "uio_pci_generic";
 	gdev->info.version = DRIVER_VERSION;
-	gdev->info.irq = pdev->irq;
-	gdev->info.irq_flags = IRQF_SHARED;
-	gdev->info.handler = irqhandler;
-	gdev->pdev = pdev;
+	gdev->info.ioctl = uio_pci_generic_ioctl;
+	mutex_init(&gdev->msix_state_lock);
+
+	err = pci_request_regions(pdev, "uio_pci_generic");
+	if (err != 0) {
+		dev_err(&pdev->dev, "Cannot request regions\n");
+		goto err_request_regions;
+	}
+
+	/* Enable the corresponding interrupt mode. Try to enable INT#X first
+	 * for backward compatibility.
+	 */
+	if (enable_intx(gdev))
+		dev_info(&pdev->dev, "Using INT#x mode: IRQ %ld",
+			 gdev->info.irq);
+	else if (enable_msix(gdev))
+		dev_info(&pdev->dev, "Using MSI-X mode: number of IRQs %d",
+			 gdev->msix.num_irqs);
+	else if (enable_msi(gdev))
+		dev_info(&pdev->dev, "Using MSI mode: IRQ %ld", gdev->info.irq);
+	else {
+		err = -ENODEV;
+		goto err_verify;
+	}
+
+	/* remap resources */
+	err = setup_maps(pdev, &gdev->info);
+	if (err)
+		goto err_maps;
 
 	err = uio_register_device(&pdev->dev, &gdev->info);
 	if (err)
 		goto err_register;
+
 	pci_set_drvdata(pdev, gdev);
 
 	return 0;
+
 err_register:
+	release_iomaps(gdev);
+err_maps:
+	disable_intr(gdev);
+err_verify:
+	pci_release_regions(pdev);
+err_request_regions:
 	kfree(gdev);
 err_alloc:
-err_verify:
 	pci_disable_device(pdev);
+
 	return err;
 }
 
@@ -110,8 +470,12 @@ static void remove(struct pci_dev *pdev)
 	struct uio_pci_generic_dev *gdev = pci_get_drvdata(pdev);
 
 	uio_unregister_device(&gdev->info);
-	pci_disable_device(pdev);
+	disable_intr(gdev);
+	release_iomaps(gdev);
+	pci_release_regions(pdev);
 	kfree(gdev);
+	pci_disable_device(pdev);
+	pci_set_drvdata(pdev, NULL);
 }
 
 static struct pci_driver uio_pci_driver = {
diff --git a/include/linux/uio_pci_generic.h b/include/linux/uio_pci_generic.h
new file mode 100644
index 0000000..10716fc
--- /dev/null
+++ b/include/linux/uio_pci_generic.h
@@ -0,0 +1,36 @@
+/*
+ * include/linux/uio_pci_generic.h
+ *
+ * Userspace generic PCI IO driver.
+ *
+ * Licensed under the GPLv2 only.
+ */
+
+#ifndef _UIO_PCI_GENERIC_H_
+#define _UIO_PCI_GENERIC_H_
+
+#include <linux/ioctl.h>
+
+enum uio_int_mode {
+	UIO_INT_MODE_NONE,
+	UIO_INT_MODE_INTX,
+	UIO_INT_MODE_MSI,
+	UIO_INT_MODE_MSIX
+};
+
+/* bind the requested IRQ to the given eventfd */
+struct uio_pci_generic_irq_set {
+	int vec; /* index of the IRQ to connect to starting from 0 */
+	int fd;
+};
+
+#define UIO_PCI_GENERIC_BASE		0x86
+
+#define UIO_PCI_GENERIC_IRQ_SET		_IOW('I', UIO_PCI_GENERIC_BASE + 1, \
+		struct uio_pci_generic_irq_set)
+#define UIO_PCI_GENERIC_IRQ_NUM_GET	_IOW('I', UIO_PCI_GENERIC_BASE + 2, \
+		uint32_t)
+#define UIO_PCI_GENERIC_INT_MODE_GET	_IOW('I', UIO_PCI_GENERIC_BASE + 3, \
+		uint32_t)
+
+#endif /* _UIO_PCI_GENERIC_H_ */
-- 
2.1.0

[PATCH v2 3/3] Documentation: update uio-howto

[Vlad Zolotarov]

Change the chapters related to uio_pci_generic that refer interrupt mode.
Add the relevant explanation regarding MSI and MSI-X interrupt modes
support.

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
---
 Documentation/DocBook/uio-howto.tmpl | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
index cd0e452..a176129 100644
--- a/Documentation/DocBook/uio-howto.tmpl
+++ b/Documentation/DocBook/uio-howto.tmpl
@@ -46,6 +46,12 @@ GPL version 2.
 
 <revhistory>
 	<revision>
+	<revnumber>0.10</revnumber>
+	<date>2015-10-04</date>
+	<authorinitials>vz</authorinitials>
+	<revremark>Added MSI and MSI-X support to uio_pci_generic.</revremark>
+	</revision>
+	<revision>
 	<revnumber>0.9</revnumber>
 	<date>2009-07-16</date>
 	<authorinitials>mst</authorinitials>
@@ -935,15 +941,32 @@ and look in the output for failure reasons
 <sect1 id="uio_pci_generic_internals">
 <title>Things to know about uio_pci_generic</title>
 	<para>
-Interrupts are handled using the Interrupt Disable bit in the PCI command
+Interrupts are handled either as MSI-X or MSI interrupts (if the device supports it) or
+as legacy INTx interrupts. By default INTx interrupts are used.
+	</para>
+	<para>
+uio_pci_generic automatically configures a device to use INTx interrupt for backward
+compatibility. If INTx are not available MSI-X interrupts will be used if the device
+supports it and if not MSI interrupts are going to be used. If none of the interrupts
+modes is supported probe() will fail.
+	</para>
+	<para>
+To get the used interrupt mode application has to use UIO_PCI_GENERIC_INT_MODE_GET ioctl
+command.
+UIO_PCI_GENERIC_IRQ_NUM_GET ioctl command may be used to get the total number of IRQs.
+Then UIO_PCI_GENERIC_IRQ_SET ioctl command may be used to bind a specific eventfd to a specific
+IRQ vector.
+	</para>
+	<para>
+Legacy interrupts are handled using the Interrupt Disable bit in the PCI command
 register and Interrupt Status bit in the PCI status register.  All devices
 compliant to PCI 2.3 (circa 2002) and all compliant PCI Express devices should
 support these bits.  uio_pci_generic detects this support, and won't bind to
 devices which do not support the Interrupt Disable Bit in the command register.
 	</para>
 	<para>
-On each interrupt, uio_pci_generic sets the Interrupt Disable bit.
-This prevents the device from generating further interrupts
+If legacy interrupts are used, uio_pci_generic sets the Interrupt Disable bit on
+each interrupt. This prevents the device from generating further interrupts
 until the bit is cleared. The userspace driver should clear this
 bit before blocking and waiting for more interrupts.
 	</para>
-- 
2.1.0