PCI: create revision file in sysfs

From: Emil Velikov <emil.velikov@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.

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

Cc: Jammy Zhou <Jammy.Zhou@amd.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
---
Gents, I'm not subscribed to the mailing list so please keep me in the
CC chain.

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

On Tue, Nov 1, 2016 at 11:42 AM, Emil Velikov <emil.l.velikov@gmail.com> wrote:
> From: Emil Velikov <emil.velikov@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.
>
> Expose the revision as a separate file, just like we do for the device,
> vendor, their subsystem version and class.
>
> Cc: Jammy Zhou <Jammy.Zhou@amd.com>
> Cc: Michel Dänzer <michel.daenzer@amd.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: linux-pci@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

> ---
> Gents, I'm not subscribed to the mailing list so please keep me in the
> CC chain.
>
> 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
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
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[Dropping Jammy since his email bounces]

On 1 November 2016 at 15:47, Alex Deucher <alexdeucher@gmail.com> wrote:
> On Tue, Nov 1, 2016 at 11:42 AM, Emil Velikov <emil.l.velikov@gmail.com> wrote:
>> From: Emil Velikov <emil.velikov@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.
>>
>> Expose the revision as a separate file, just like we do for the device,
>> vendor, their subsystem version and class.
>>
>> Cc: Jammy Zhou <Jammy.Zhou@amd.com>
>> Cc: Michel Dänzer <michel.daenzer@amd.com>
>> Cc: Bjorn Helgaas <bhelgaas@google.com>
>> Cc: linux-pci@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
>
> Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
>
Thanks Alex.

Gents, to elaborate a bit:

When using the Mesa drivers alongside firefox [1] (since Mesa 13.0),
glxinfo (Mesa 10.0) and others, all the GPUs* will be awaken, causing
unwanted delays and increased power usage.
From the userspace POV we have two distinct users who require the
revision file - libdrm and libpciaccess. * The latter would even wake
up _all_ the devices located on a PCI bus !

Let me know if you'd like the above in the patch summary, meanwhile
I'll poke and collect a few more ack/r-b/t-b.

Thanks
Emil

[1] https://bugs.freedesktop.org/show_bug.cgi?id=98502
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