[Intel-gfx] [PATCH] drm/i915: Acquire RPM wakeref for KMS atomic commit

Chris Wilson chris at chris-wilson.co.uk
Mon Dec 21 08:14:53 PST 2015

On Mon, Dec 21, 2015 at 05:02:08PM +0100, Daniel Vetter wrote:
> On Sat, Dec 19, 2015 at 09:58:43AM +0000, Chris Wilson wrote:
> > Once all the preparations are complete, we are ready to write the
> > modesetting to the hardware. During this phase, we will be making lots
> > of HW register access, so take a top level wakeref to prevent an
> > unwarranted rpm suspend cycle mid-commit. Lower level functions should
> > be waking the individual power wells as required.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93439
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Imre Deak <imre.deak at intel.com>
> The original idea here was that doing this will paper over bugs in our rpm
> refcounting. There's also the problem that for modeset stuff we have all
> the power wells still to take care of.
> For the referenced bug we should add a power domain check in the get hw
> state function instead, which is what we've been doing with all the other
> similar hw state readout functions too.

Agreed that there is another bug, but in the long term, we do want a
"prolonged" wakeref here. In the next evolution of the wakeref assertions,
we should be able to differentiate between the two (i.e. when we have
fine grained wakerefs around the hw access, we need to assert we hold one
of that type in the mmio accessor, rather than the prolonged version).

Chris Wilson, Intel Open Source Technology Centre

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