uio: add generic driver for PCI 2.3 devices

This adds a generic uio driver that can bind to any PCI device.  First
user will be virtualization where a qemu userspace process needs to give
guest OS access to the device.

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.  Driver detects this support,
and won't bind to devices which do not support the Interrupt Disable Bit
in the command register.

It's expected that more features of interest to virtualization will be
added to this driver in the future. Possibilities are: mmap for device
resources, MSI/MSI-X, eventfd (to interface with kvm), iommu.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Hans J. Koch <hjk@linutronix.de>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/DocBook/uio-howto.tmpl

@@ -25,6 +25,10 @@
 	<year>2006-2008</year>
 	<holder>Hans-Jürgen Koch.</holder>
 </copyright>
+<copyright>
+	<year>2009</year>
+	<holder>Red Hat Inc, Michael S. Tsirkin (mst@redhat.com)</holder>
+</copyright>
 
 <legalnotice>
 <para>
@@ -41,6 +45,13 @@ GPL version 2.
 </abstract>
 
 <revhistory>
+	<revision>
+	<revnumber>0.9</revnumber>
+	<date>2009-07-16</date>
+	<authorinitials>mst</authorinitials>
+	<revremark>Added generic pci driver
+		</revremark>
+	</revision>
 	<revision>
 	<revnumber>0.8</revnumber>
 	<date>2008-12-24</date>
@@ -809,6 +820,158 @@ framework to set up sysfs files for this region. Simply leave it alone.
 
 </chapter>
 
+<chapter id="uio_pci_generic" xreflabel="Using Generic driver for PCI cards">
+<?dbhtml filename="uio_pci_generic.html"?>
+<title>Generic PCI UIO driver</title>
+	<para>
+	The generic driver is a kernel module named uio_pci_generic.
+	It can work with any device compliant to PCI 2.3 (circa 2002) and
+	any compliant PCI Express device. Using this, you only need to
+        write the userspace driver, removing the need to write
+        a hardware-specific kernel module.
+	</para>
+
+<sect1 id="uio_pci_generic_binding">
+<title>Making the driver recognize the device</title>
+	<para>
+Since the driver does not declare any device ids, it will not get loaded
+automatically and will not automatically bind to any devices, you must load it
+and allocate id to the driver yourself. For example:
+	<programlisting>
+ modprobe uio_pci_generic
+ echo &quot;8086 10f5&quot; &gt; /sys/bus/pci/drivers/uio_pci_generic/new_id
+	</programlisting>
+	</para>
+	<para>
+If there already is a hardware specific kernel driver for your device, the
+generic driver still won't bind to it, in this case if you want to use the
+generic driver (why would you?) you'll have to manually unbind the hardware
+specific driver and bind the generic driver, like this:
+	<programlisting>
+    echo -n 0000:00:19.0 &gt; /sys/bus/pci/drivers/e1000e/unbind
+    echo -n 0000:00:19.0 &gt; /sys/bus/pci/drivers/uio_pci_generic/bind
+	</programlisting>
+	</para>
+	<para>
+You can verify that the device has been bound to the driver
+by looking for it in sysfs, for example like the following:
+	<programlisting>
+    ls -l /sys/bus/pci/devices/0000:00:19.0/driver
+	</programlisting>
+Which if successful should print
+	<programlisting>
+  .../0000:00:19.0/driver -&gt; ../../../bus/pci/drivers/uio_pci_generic
+	</programlisting>
+Note that the generic driver will not bind to old PCI 2.2 devices.
+If binding the device failed, run the following command:
+	<programlisting>
+  dmesg
+	</programlisting>
+and look in the output for failure reasons
+	</para>
+</sect1>
+
+<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
+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
+until the bit is cleared. The userspace driver should clear this
+bit before blocking and waiting for more interrupts.
+	</para>
+</sect1>
+<sect1 id="uio_pci_generic_userspace">
+<title>Writing userspace driver using uio_pci_generic</title>
+	<para>
+Userspace driver can use pci sysfs interface, or the
+libpci libray that wraps it, to talk to the device and to
+re-enable interrupts by writing to the command register.
+	</para>
+</sect1>
+<sect1 id="uio_pci_generic_example">
+<title>Example code using uio_pci_generic</title>
+	<para>
+Here is some sample userspace driver code using uio_pci_generic:
+<programlisting>
+#include &lt;stdlib.h&gt;
+#include &lt;stdio.h&gt;
+#include &lt;unistd.h&gt;
+#include &lt;sys/types.h&gt;
+#include &lt;sys/stat.h&gt;
+#include &lt;fcntl.h&gt;
+#include &lt;errno.h&gt;
+
+int main()
+{
+	int uiofd;
+	int configfd;
+	int err;
+	int i;
+	unsigned icount;
+	unsigned char command_high;
+
+	uiofd = open(&quot;/dev/uio0&quot;, O_RDONLY);
+	if (uiofd &lt; 0) {
+		perror(&quot;uio open:&quot;);
+		return errno;
+	}
+	configfd = open(&quot;/sys/class/uio/uio0/device/config&quot;, O_RDWR);
+	if (uiofd &lt; 0) {
+		perror(&quot;config open:&quot;);
+		return errno;
+	}
+
+	/* Read and cache command value */
+	err = pread(configfd, &amp;command_high, 1, 5);
+	if (err != 1) {
+		perror(&quot;command config read:&quot;);
+		return errno;
+	}
+	command_high &amp;= ~0x4;
+
+	for(i = 0;; ++i) {
+		/* Print out a message, for debugging. */
+		if (i == 0)
+			fprintf(stderr, &quot;Started uio test driver.\n&quot;);
+		else
+			fprintf(stderr, &quot;Interrupts: %d\n&quot;, icount);
+
+		/****************************************/
+		/* Here we got an interrupt from the
+		   device. Do something to it. */
+		/****************************************/
+
+		/* Re-enable interrupts. */
+		err = pwrite(configfd, &amp;command_high, 1, 5);
+		if (err != 1) {
+			perror(&quot;config write:&quot;);
+			break;
+		}
+
+		/* Wait for next interrupt. */
+		err = read(uiofd, &amp;icount, 4);
+		if (err != 4) {
+			perror(&quot;uio read:&quot;);
+			break;
+		}
+
+	}
+	return errno;
+}
+
+</programlisting>
+	</para>
+</sect1>
+
+</chapter>
+
 <appendix id="app1">
 <title>Further information</title>
 <itemizedlist>

MAINTAINERS

@@ -2218,6 +2218,13 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic.git
 S:	Maintained
 F:	include/asm-generic
 
+GENERIC UIO DRIVER FOR PCI DEVICES
+M:	Michael S. Tsirkin <mst@redhat.com>
+L:	kvm@vger.kernel.org
+L:	linux-kernel@vger.kernel.org
+S:	Supported
+F:	drivers/uio/uio_pci_generic.c
+
 GFS2 FILE SYSTEM
 M:	Steven Whitehouse <swhiteho@redhat.com>
 L:	cluster-devel@redhat.com

drivers/uio/Kconfig

@@ -84,4 +84,14 @@ config UIO_SERCOS3
 
 	  If you compile this as a module, it will be called uio_sercos3.
 
+config UIO_PCI_GENERIC
+	tristate "Generic driver for PCI 2.3 and PCI Express cards"
+	depends on PCI
+	default n
+	help
+	  Generic driver that you can bind, dynamically, to any
+	  PCI 2.3 compliant and PCI Express card. It is useful,
+	  primarily, for virtualization scenarios.
+	  If you compile this as a module, it will be called uio_pci_generic.
+
 endif

drivers/uio/Makefile

@@ -5,3 +5,4 @@ obj-$(CONFIG_UIO_PDRV_GENIRQ)	+= uio_pdrv_genirq.o
 obj-$(CONFIG_UIO_SMX)	+= uio_smx.o
 obj-$(CONFIG_UIO_AEC)	+= uio_aec.o
 obj-$(CONFIG_UIO_SERCOS3)	+= uio_sercos3.o
+obj-$(CONFIG_UIO_PCI_GENERIC)	+= uio_pci_generic.o

drivers/uio/uio_pci_generic.c

@@ -0,0 +1,207 @@
+/* uio_pci_generic - generic UIO driver for PCI 2.3 devices
+ *
+ * Copyright (C) 2009 Red Hat, Inc.
+ * Author: Michael S. Tsirkin <mst@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ * Since the driver does not declare any device ids, you must allocate
+ * id and bind the device to the driver yourself.  For example:
+ *
+ * # echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id
+ * # echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind
+ * # echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind
+ * # ls -l /sys/bus/pci/devices/0000:00:19.0/driver
+ * .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic
+ *
+ * Driver won't bind to devices which do not support the Interrupt Disable Bit
+ * in the command register. All devices compliant to PCI 2.3 (circa 2002) and
+ * all compliant PCI Express devices should support this bit.
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/uio_driver.h>
+#include <linux/spinlock.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 uio_pci_generic_dev {
+	struct uio_info info;
+	struct pci_dev *pdev;
+	spinlock_t lock; /* guards command register accesses */
+};
+
+static inline struct uio_pci_generic_dev *
+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)
+{
+	struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
+	struct pci_dev *pdev = gdev->pdev;
+	irqreturn_t ret = IRQ_NONE;
+	u32 cmd_status_dword;
+	u16 origcmd, newcmd, status;
+
+	/* We do a single dword read to retrieve both command and status.
+	 * Document assumptions that make this possible. */
+	BUILD_BUG_ON(PCI_COMMAND % 4);
+	BUILD_BUG_ON(PCI_COMMAND + 2 != PCI_STATUS);
+
+	spin_lock_irq(&gdev->lock);
+	pci_block_user_cfg_access(pdev);
+
+	/* Read both command and status registers in a single 32-bit operation.
+	 * Note: we could cache the value for command and move the status read
+	 * out of the lock if there was a way to get notified of user changes
+	 * to command register through sysfs. Should be good for shared irqs. */
+	pci_read_config_dword(pdev, PCI_COMMAND, &cmd_status_dword);
+	origcmd = cmd_status_dword;
+	status = cmd_status_dword >> 16;
+
+	/* Check interrupt status register to see whether our device
+	 * triggered the interrupt. */
+	if (!(status & PCI_STATUS_INTERRUPT))
+		goto done;
+
+	/* We triggered the interrupt, disable it. */
+	newcmd = origcmd | PCI_COMMAND_INTX_DISABLE;
+	if (newcmd != origcmd)
+		pci_write_config_word(pdev, PCI_COMMAND, newcmd);
+
+	/* UIO core will signal the user process. */
+	ret = IRQ_HANDLED;
+done:
+
+	pci_unblock_user_cfg_access(pdev);
+	spin_unlock_irq(&gdev->lock);
+	return ret;
+}
+
+/* Verify that the device supports Interrupt Disable bit in command register,
+ * per PCI 2.3, by flipping this bit and reading it back: this bit was readonly
+ * in PCI 2.2. */
+static int __devinit verify_pci_2_3(struct pci_dev *pdev)
+{
+	u16 orig, new;
+	int err = 0;
+
+	pci_block_user_cfg_access(pdev);
+	pci_read_config_word(pdev, PCI_COMMAND, &orig);
+	pci_write_config_word(pdev, PCI_COMMAND,
+			      orig ^ PCI_COMMAND_INTX_DISABLE);
+	pci_read_config_word(pdev, PCI_COMMAND, &new);
+	/* There's no way to protect against
+	 * hardware bugs or detect them reliably, but as long as we know
+	 * what the value should be, let's go ahead and check it. */
+	if ((new ^ orig) & ~PCI_COMMAND_INTX_DISABLE) {
+		err = -EBUSY;
+		dev_err(&pdev->dev, "Command changed from 0x%x to 0x%x: "
+			"driver or HW bug?\n", orig, new);
+		goto err;
+	}
+	if (!((new ^ orig) & PCI_COMMAND_INTX_DISABLE)) {
+		dev_warn(&pdev->dev, "Device does not support "
+			 "disabling interrupts: unable to bind.\n");
+		err = -ENODEV;
+		goto err;
+	}
+	/* Now restore the original value. */
+	pci_write_config_word(pdev, PCI_COMMAND, orig);
+err:
+	pci_unblock_user_cfg_access(pdev);
+	return err;
+}
+
+static int __devinit probe(struct pci_dev *pdev,
+			   const struct pci_device_id *id)
+{
+	struct uio_pci_generic_dev *gdev;
+	int err;
+
+	if (!pdev->irq) {
+		dev_warn(&pdev->dev, "No IRQ assigned to device: "
+			 "no support for interrupts?\n");
+		return -ENODEV;
+	}
+
+	err = pci_enable_device(pdev);
+	if (err) {
+		dev_err(&pdev->dev, "%s: pci_enable_device failed: %d\n",
+			__func__, err);
+		return err;
+	}
+
+	err = verify_pci_2_3(pdev);
+	if (err)
+		goto err_verify;
+
+	gdev = kzalloc(sizeof(struct uio_pci_generic_dev), GFP_KERNEL);
+	if (!gdev) {
+		err = -ENOMEM;
+		goto err_alloc;
+	}
+
+	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;
+	spin_lock_init(&gdev->lock);
+
+	if (uio_register_device(&pdev->dev, &gdev->info))
+		goto err_register;
+	pci_set_drvdata(pdev, gdev);
+
+	return 0;
+err_register:
+	kfree(gdev);
+err_alloc:
+err_verify:
+	pci_disable_device(pdev);
+	return err;
+}
+
+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);
+	kfree(gdev);
+}
+
+static struct pci_driver driver = {
+	.name = "uio_pci_generic",
+	.id_table = NULL, /* only dynamic id's */
+	.probe = probe,
+	.remove = remove,
+};
+
+static int __init init(void)
+{
+	pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
+	return pci_register_driver(&driver);
+}
+
+static void __exit cleanup(void)
+{
+	pci_unregister_driver(&driver);
+}
+
+module_init(init);
+module_exit(cleanup);
+
+MODULE_VERSION(DRIVER_VERSION);
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);

include/linux/pci_regs.h

@@ -42,6 +42,7 @@
 #define  PCI_COMMAND_INTX_DISABLE 0x400 /* INTx Emulation Disable */
 
 #define PCI_STATUS		0x06	/* 16 bits */
+#define  PCI_STATUS_INTERRUPT	0x08	/* Interrupt status */
 #define  PCI_STATUS_CAP_LIST	0x10	/* Support Capability List */
 #define  PCI_STATUS_66MHZ	0x20	/* Support 66 Mhz PCI 2.1 bus */
 #define  PCI_STATUS_UDF		0x40	/* Support User Definable Features [obsolete] */