[Intel-gfx] [PATCH 5/5] drm/i915: Estimate and update missed vblanks.

[Daniel Vetter]

On Fri, Jan 12, 2018 at 01:57:07PM -0800, Dhinakaran Pandiyan wrote:
> The frame counter may have got reset between disabling and enabling vblank
> interrupts due to DMC putting the hardware to DC5/6 state if PSR was
> active. The frame counter also could have stalled if PSR is active in cases
> where there is no DMC. The frame counter resetting as a user visible impact
> of screen freezes. Use drm_vblank_restore() to compute missed vblanks
> in the duration for which vblank interrupts are disabled. There's no need
> particularly check if PSR was active in the interrupt disabled duration.
> 
> Enabling vblank interrupts wakes up the hardware from DC5/6 and prevents it
> from going back again as long as the there are pending interrupts. So, we
> don't have to explicity disallow DC5/6 after enabling vblank interrupts
> to keep the counter running.
> 
> Let's not apply this to CHV for now, as enabling interrupts does not
> prevent the hardware from activating PSR and thereby stalling the counter.
> 
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>

Read this series, and I think compared to all the previous attempts to fix
this issue this one here seems the cleanest. Not an expert on the vblank
code (Michel or Ville are best for that), but on the series:

Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Cheers, Daniel
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 3517c6548e2c..db3466ec6faa 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2956,6 +2956,9 @@ static int ironlake_enable_vblank(struct drm_device *dev, unsigned int pipe)
>  	ilk_enable_display_irq(dev_priv, bit);
>  	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
>  
> +	if (HAS_PSR(dev_priv))
> +		drm_vblank_restore(dev, pipe);
> +
>  	return 0;
>  }
>  
> @@ -2968,6 +2971,9 @@ static int gen8_enable_vblank(struct drm_device *dev, unsigned int pipe)
>  	bdw_enable_pipe_irq(dev_priv, pipe, GEN8_PIPE_VBLANK);
>  	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
>  
> +	if (HAS_PSR(dev_priv))
> +		drm_vblank_restore(dev, pipe);
> +
>  	return 0;
>  }
>  
> -- 
> 2.11.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch