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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 16 Dec 2014, Daniel Vetter <daniel@ffwll.ch> wrote:
> 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?

At least the partial fix referenced is in 3.17.

> -Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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-- 
Jani Nikula, Intel Open Source Technology Center
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