Re: [PATCH v5 1/5] drm/i915: Add enable/disable flip done and flip done handler

["Michel Dänzer" <michel@daenzer.net>]

On 2020-07-25 1:26 a.m., Paulo Zanoni wrote:
> Em seg, 2020-07-20 às 17:01 +0530, Karthik B S escreveu:
>>
>> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
>> index 1fa67700d8f4..95953b393941 100644
>> --- a/drivers/gpu/drm/i915/i915_irq.c
>> +++ b/drivers/gpu/drm/i915/i915_irq.c
>> @@ -697,14 +697,24 @@ u32 i915_get_vblank_counter(struct drm_crtc *crtc)
>>  	return (((high1 << 8) | low) + (pixel >= vbl_start)) & 0xffffff;
>>  }
>>  
>> +static u32 g4x_get_flip_counter(struct drm_crtc *crtc)
>> +{
>> +	struct drm_i915_private *dev_priv = to_i915(crtc->dev);
>> +	enum pipe pipe = to_intel_crtc(crtc)->pipe;
>> +
>> +	return I915_READ(PIPE_FLIPCOUNT_G4X(pipe));
>> +}
>> +
>>  u32 g4x_get_vblank_counter(struct drm_crtc *crtc)
>>  {
>>  	struct drm_i915_private *dev_priv = to_i915(crtc->dev);
>>  	enum pipe pipe = to_intel_crtc(crtc)->pipe;
>>  
>> +	if (crtc->state->async_flip)
>> +		return g4x_get_flip_counter(crtc);
>> +
>>  	return I915_READ(PIPE_FRMCOUNT_G4X(pipe));
> 
> I don't understand the intention behind this, can you please clarify?
> This goes back to my reply of the cover letter. It seems that here
> we're going to alternate between two different counters in our vblank
> count. So if user space alternates between sometimes using async flips
> and sometimes using normal flip it's going to get some very weird
> deltas, isn't it? At least this is what I remember from when I played
> with these registers: FLIPCOUNT drifts away from FRMCOUNT when we start
> using async flips.

This definitely looks wrong. The counter value returned by the
get_vblank_counter hook is supposed to increment when a vertical blank
period occurs; page flips are not supposed to affect this in any way.


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer
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