[Intel-gfx] [PATCH 6/6] drm/i915: Sanitize drm crtc vblank counter after DC reset frame count.

[Rodrigo Vivi]

On Thu, Aug 4, 2016 at 1:26 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, Aug 03, 2016 at 02:33:39PM -0700, Rodrigo Vivi wrote:
>> DC state reset the frame counter that is a read-only register.
>>
>> So, besides blocking DC state on vblank let's restore the
>> drm crtc vblank counter to a place we know it is reliable.
>>
>> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_irq.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
>> index 4efe20c..82d6896 100644
>> --- a/drivers/gpu/drm/i915/i915_irq.c
>> +++ b/drivers/gpu/drm/i915/i915_irq.c
>> @@ -2759,7 +2759,9 @@ static int gen8_enable_vblank(struct drm_device *dev, unsigned int pipe)
>>  static void gen9_prepare_vblank(struct drm_device *dev, unsigned int pipe)
>>  {
>>       struct drm_i915_private *dev_priv = to_i915(dev);
>> +     struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
>>       intel_display_power_get(dev_priv, POWER_DOMAIN_VBLANK);
>> +     drm_crtc_vblank_sanitize_counter(crtc);
>
> I think this should be done within the platform power code. Otherwise
> something else might keep the system out of dc states, but then we might
> wreak havoc by calling this function here.

This is safe here because DC is handled as a power_well... so as long
as there is one domain holding its reference DC will be off.

Also this needs to be in a place we are sure that vblanks are yet disabled.

Now it comes back to that point on how to make sure that we only run 1
prepare pre-enable...

multiple prepare/unprepares will keep trying to resync it useless and
if we have that WARN_ON we will get flooded....

> -Daniel
>
>>  }
>>
>>  static void gen9_unprepare_vblank(struct drm_device *dev, unsigned int pipe)
>> --
>> 2.4.3
>>
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>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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-- 
Rodrigo Vivi
Blog: http://blog.vivi.eng.br