Re: [PATCH] drm/i915: Hold runtime PM during plane commit

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Dec 15, 2014 at 04:30:44PM -0200, Paulo Zanoni wrote:
> 2014-12-15 16:11 GMT-02:00 Matt Roper <matthew.d.roper@intel.com>:
> > During plane operations, we read/write some registers that only operate
> > properly if we're not runtime suspended.  At the moment we're not
> > holding the runtime PM reference across the whole plane operation, so
> > there's a potential for problems.
> >
> > This issue was already partially addressed by commit
> >
> >         commit d6dd6843ff4a57c662dbc378b9f99a9c034b0956
> >         Author: Paulo Zanoni <paulo.r.zanoni@intel.com>
> >         Date:   Fri Aug 15 15:59:32 2014 -0300
> >
> >             drm/i915: fix plane/cursor handling when runtime suspended
> >
> > which took care of holding the runtime PM reference during the pin and
> > fence operations for plane updates.  However there are still a few
> > actual plane registers that we also need to hold the runtime PM
> > reference for.  Recent refactoring patches in preparation for atomic
> > have rearranged the code and made it increasingly likely that the
> > hardware will have time to suspend between the pin/fence operation and
> > the actual register writes.

Which kind of registers? If this is just in the system agent then a rpm
ref is enough, but if this is also about plane registers then we'd need a
reference of the plane power domain. Which would indicate some failure to
check for crtc->active somewhere I think.

> > The solution here grabs the runtime PM reference around the 'commit'
> > operation for planes, which should cover all the relevant register
> > reads/writes.
> >
> > Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=87180
> > Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> 
> I see we're in the middle of a very big rework on how all these
> prepare/commit functions are called, so I don't think it makes sense
> to spend too much time trying to find the very-best-perfect spot for
> the get/put calls, since they're likely to be changed later. So I
> guess that for now it's important to fix the current "regression"
> reported by QA:
> 
> Testcase: igt/pm-rpm/legacy-planes
> Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

Also Cc: stable@vger.kernel.org I guess? Or is this only for dinq?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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