[PATCH v2] 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 delays.

There are at least two userspace components which could make use the new
file - libpciaccess and libdrm. At the moment the former will wake up
_every_ PCI device for simple invocation of 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
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.

As before, please keep me in the CC list. Additionally if there's
anything else I can do to get things going please let me know.

Thanks
Emil
---
 drivers/pci/pci-sysfs.c | 2 ++
 1 file changed, 2 insertions(+)

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