Re: [Intel-gfx] [PATCH v2] drm/i915: Do a better job at disabling primary plane in the noatomic case.

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

On Thu, 10 Dec 2015, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Mon, Nov 23, 2015 at 10:25:28AM +0100, Maarten Lankhorst wrote:
>> Op 13-11-15 om 14:28 schreef Ander Conselvan De Oliveira:
>> > On Thu, 2015-11-12 at 14:58 +0100, Maarten Lankhorst wrote:
>> >> Op 12-11-15 om 14:37 schreef Ander Conselvan De Oliveira:
>> >>> On Wed, 2015-11-11 at 15:36 +0100, Maarten Lankhorst wrote:
>> >>>> When disable_noatomic is called plane_mask is not reliable yet,
>> >>>> and plane_state->visible = true even after disabling the primary plane.
>> >>> So the stale value of plane_state->visible causes a subsequent modeset to
>> >>> enable
>> >>> the primary again?
>> >> Probably not because it would get recalculated in calc_changes, but it should
>> >> really be set to false afterwards.
>> > So basically I didn't understand how the wrong value of plane_state->visible
>> > causes the bug that was mentioned. I think a brief explanation in the commit
>> > message would be good.
>> Well, apply with git am --scissors. Same patch but mentioning this.
>> 
>> Is this better?
>> ---->8-----
>> 
>> When disable_noatomic is called plane_mask is not correct yet,
>> and plane_state->visible = true is left as true after disabling
>> the primary plane.
>> 
>> Other planes are already disabled as part of crtc sanitization, only the
>> primary is left active. But the plane_mask is not updated here. It gets updated
>> during fb takeover in modeset_gem_init, or set to the new value on resume.
>> 
>> This means that to disable the primary plane 1 << drm_plane_index(primary)
>> needs to be used.
>> 
>> Afterwards because the crtc is no longer active it's forbidden to keep
>> plane_state->visible set, or a WARN_ON in intel_plane_atomic_calc_changes
>> triggers. There are other code points that rely on accurate plane_state->visible
>> too, so make sure the bool is cleared.
>
> Oh dear is this a mess :(
>
> As a bugfix this is Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Pushed to drm-intel-fixes, thanks for the patch and review.

BR,
Jani.

>
> But we need to bring a _lot_ more sanity to this in -next. Would probably
> be better if we keep the primary plane state all consistent, and then
> clear both visible and plane_mask when fb reconstruction fails.
>
> Also, some WARN_ON to bitch about inconsistency between plane_mask and
> ->visible in the disable code paths would be good I think.
> -Daniel
>
>> 
>> 
>> The other planes are already disabled in intel_sanitize_crtc, so
>> they don't have to be handled here.
>> 
>> Cc: stable@vger.kernel.org #v4.3, v4.2?
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92655
>> Tested-by: Tomas Mezzadra <tmezzadra@gmail.com>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_display.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> index b5f7493213b7..bc3282ab5ed2 100644
>> --- a/drivers/gpu/drm/i915/intel_display.c
>> +++ b/drivers/gpu/drm/i915/intel_display.c
>> @@ -6267,9 +6267,11 @@ static void intel_crtc_disable_noatomic(struct drm_crtc *crtc)
>>  		WARN_ON(intel_crtc->unpin_work);
>>  
>>  		intel_pre_disable_primary(crtc);
>> +
>> +		intel_crtc_disable_planes(crtc, 1 << drm_plane_index(crtc->primary));
>> +		to_intel_plane_state(crtc->primary->state)->visible = false;
>>  	}
>>  
>> -	intel_crtc_disable_planes(crtc, crtc->state->plane_mask);
>>  	dev_priv->display.crtc_disable(crtc);
>>  	intel_crtc->active = false;
>>  	intel_update_watermarks(crtc);
>> -- 2.1.0
>> 
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-- 
Jani Nikula, Intel Open Source Technology Center