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