[PATCH v3] PCI: create revision file in sysfs

[Bjorn Helgaas]

On Fri, Nov 18, 2016 at 10:42:20AM +0900, Michel Dänzer wrote:
> On 18/11/16 08:48 AM, Bjorn Helgaas wrote:
> > 
> > Popping the stack all the way back to Emil's Nov 8 message:
> > 
> >   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.
> > 
> >   [1] https://bugs.freedesktop.org/show_bug.cgi?id=98502
> > 
> > The bug is about a delay in starting firefox, thunderbird, or
> > chromium.  I assume the browser starts on the current, powered-up,
> > GPU.  I don't understand why we care about the revision of other,
> > powered-off, GPUs.
> 
> We don't. The problem is that the current libdrm API unconditionally
> provides the revision. The plan is to address this in two ways:
> 
> * Add new libdrm API which allows the caller to say "I don't need the
> revision", and make Mesa use that. Users having those changes will not
> run into the problem even on older kernels.
> 
> * Add the separate revision file in sysfs and make libdrm use that for
> its current API. This means that even callers of the current libdrm API
> will not run into the problem with newer kernels.

Why do we care about *anything* for the other, powered-off, GPUs?
Even users of the new libdrm API who say "I don't need the revision"
are still getting the vendor/device/etc for those other GPUs.