Re: [PATCH 2/5] drm: Add initial dnyamic power off feature

[Chris Wilson <chris@chris-wilson.co.uk>]

On Mon, 10 Sep 2012 18:23:05 +1000, Dave Airlie <airlied@gmail.com> wrote:
> (oops' forgot reply to all)
> 
> >
> > My midlayer-smell-o-meter just cranked up to 11 when reading this comment
> > ;-)
> >
> > I'd have expected:
> > - Drivers to check the power state and enable the gpu if it's off in their
> >   cs ioctl (instead of the brute-force every ioctl there is approach in
> >   the drm core)
> 
> The problem is it won't just be the CS ioctl, so I just went with the
> larger hammer, I started annotating all the nouveau ioctls adding a
> wake up check at the top, and then realised that I need to start
> annotating all the non-gpu paths as well, like drm open, sysfs,
> basically anywhere that might cause us to access any GPU resources.
> Once I started annotating everywhere I realised just bashing it into
> the top most ioctl then sticking the whole lot into the drm core made
> sense. You have to think the device is gone completely, not the device
> is asleep. its not asleep, its effectively dead.

This reminds me of some of the power island patches that we making the
rounds a few years ago - effectively shadowing register blocks to avoid
waking up the device for trivial queries. In many ways it was just a
fine grained suspend/resume. Not sure if that concept helps here, but it
may be worth digging around to see how they went about waking up
individual devices.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre