[PATCH v3] PCI: create revision file in sysfs

[Emil Velikov]

From: Emil Velikov <emil.velikov at collabora.com>

Currently the revision isn't available via sysfs/libudev thus if one
wants to know the value they need to read through the config file.

This in itself wakes/powers up the device, causing unwanted delay
since it can be quite costly.

There are at least two userspace components which could make use the new
file libpciaccess and libdrm. The former [used in various places] wakes
up _every_ PCI device, which can be observed via glxinfo [when using
Mesa 10.0+ drivers]. While the latter [in association with Mesa 13.0]
can lead to 2-3 second delays while starting firefox, thunderbird or
chromium.

Expose the revision as a separate file, just like we do for the device,
vendor, their subsystem version and class.

Cc: Bjorn Helgaas <bhelgaas at google.com>
Cc: linux-pci at vger.kernel.org
Cc: Greg KH <gregkh at linuxfoundation.org>
Link: https://bugs.freedesktop.org/show_bug.cgi?id=98502
Tested-by: Mauro Santos <registo.mailling at gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
---
v2: Add r-b/t-b tags, slim down CC list, add note about userspace.

v3: Add Documentation/ bits (Greg KH)

Gents, please keep me in the CC list.

Thanks
Emil
---
 Documentation/ABI/testing/sysfs-bus-pci | 7 +++++++
 Documentation/filesystems/sysfs-pci.txt | 2 ++
 drivers/pci/pci-sysfs.c                 | 2 ++
 3 files changed, 11 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index b3bc50f..5a1732b 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -294,3 +294,10 @@ Description:
 		a firmware bug to the system vendor.  Writing to this file
 		taints the kernel with TAINT_FIRMWARE_WORKAROUND, which
 		reduces the supportability of your system.
+
+What:		/sys/bus/pci/devices/.../revision
+Date:		November 2016
+Contact:	Emil Velikov <emil.l.velikov at gmail.com>
+Description:
+		This file contains the revision field of the the PCI device.
+		The value comes from device config space. The file is read only.
diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
index 74eaac2..6ea1ced 100644
--- a/Documentation/filesystems/sysfs-pci.txt
+++ b/Documentation/filesystems/sysfs-pci.txt
@@ -17,6 +17,7 @@ that support it.  For example, a given bus might look like this:
      |   |-- resource0
      |   |-- resource1
      |   |-- resource2
+     |   |-- revision
      |   |-- rom
      |   |-- subsystem_device
      |   |-- subsystem_vendor
@@ -41,6 +42,7 @@ files, each with their own function.
        resource		   PCI resource host addresses (ascii, ro)
        resource0..N	   PCI resource N, if present (binary, mmap, rw[1])
        resource0_wc..N_wc  PCI WC map resource N, if prefetchable (binary, mmap)
+       revision		   PCI revision (ascii, ro)
        rom		   PCI ROM resource, if present (binary, ro)
        subsystem_device	   PCI subsystem device (ascii, ro)
        subsystem_vendor	   PCI subsystem vendor (ascii, ro)
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index bcd10c7..0666287 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -50,6 +50,7 @@ pci_config_attr(vendor, "0x%04x\n");
 pci_config_attr(device, "0x%04x\n");
 pci_config_attr(subsystem_vendor, "0x%04x\n");
 pci_config_attr(subsystem_device, "0x%04x\n");
+pci_config_attr(revision, "0x%02x\n");
 pci_config_attr(class, "0x%06x\n");
 pci_config_attr(irq, "%u\n");
 
@@ -568,6 +569,7 @@ static struct attribute *pci_dev_attrs[] = {
 	&dev_attr_device.attr,
 	&dev_attr_subsystem_vendor.attr,
 	&dev_attr_subsystem_device.attr,
+	&dev_attr_revision.attr,
 	&dev_attr_class.attr,
 	&dev_attr_irq.attr,
 	&dev_attr_local_cpus.attr,
-- 
2.9.3