linux-kernel - Re: [PATCH] PCI: create revision file in sysfs

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Date:   Tue, 8 Nov 2016 11:27:37 +0000
From:   Emil Velikov <emil.l.velikov@...il.com>
To:     Alex Deucher <alexdeucher@...il.com>
Cc:     Maling list - DRI developers <dri-devel@...ts.freedesktop.org>,
        Michel Dänzer <michel.daenzer@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] PCI: create revision file in sysfs

[Dropping Jammy since his email bounces]

On 1 November 2016 at 15:47, Alex Deucher <alexdeucher@...il.com> wrote:
> On Tue, Nov 1, 2016 at 11:42 AM, Emil Velikov <emil.l.velikov@...il.com> wrote:
>> From: Emil Velikov <emil.velikov@...labora.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@....com>
>> Cc: Michel Dänzer <michel.daenzer@....com>
>> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
>> Cc: linux-pci@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Emil Velikov <emil.velikov@...labora.com>
>
> Reviewed-by: Alex Deucher <alexander.deucher@....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