Re: [PATCH 5/5] drm/i915: Shuffle fifo underrun disable/enable points for gmch platforms

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, May 16, 2014 at 07:40:25PM +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Gen2 reports FIFO underruns whenever no planes are enabled on the pipe.
> So in order to avoid false positives we must enable the FIFO underrun
> reporting only when at least one plane is enabled on the pipe. For
> now just move the underrun reporting enable/disable points to the
> other side of the plane enable/disable point. That doesn't cover cases
> when we turn off all the planes for the pipe but leave the pipe running
> on purpose, but it's better than the current situation.
> 
> On gen4+ we can actually move the underrun reporting enable/disable to
> the opposite ends of the crtc enable/disable hooks. I suppose in theory
> we could leave the underrun reporting enabled all the time, except on
> VLV where PIPESTAT stops working when the display power well is down.
> If we ever get around to unifying the PIPESTAT irq handling for all
> gmch platforms, we should still follow the VLV route for other platforms.
> It would also micro-optimize the irq handler a bit since we could then
> skip the PIPESTAT reads for all disabled pipes.
> 
> Gen3 is still a mystery, but for now I'm going to assume it behaves
> like gen4+.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 1b5164c..7f61047 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -4514,6 +4514,8 @@ static void valleyview_crtc_enable(struct drm_crtc *crtc)
>  
>  	intel_crtc->active = true;
>  
> +	intel_set_cpu_fifo_underrun_reporting(dev, pipe, true);
> +
>  	for_each_encoder_on_crtc(dev, crtc, encoder)
>  		if (encoder->pre_pll_enable)
>  			encoder->pre_pll_enable(encoder);
> @@ -4537,7 +4539,6 @@ static void valleyview_crtc_enable(struct drm_crtc *crtc)
>  
>  	intel_update_watermarks(crtc);
>  	intel_enable_pipe(intel_crtc);
> -	intel_set_cpu_fifo_underrun_reporting(dev, pipe, true);
>  
>  	for_each_encoder_on_crtc(dev, crtc, encoder)
>  		encoder->enable(encoder);
> @@ -4564,6 +4565,9 @@ static void i9xx_crtc_enable(struct drm_crtc *crtc)
>  
>  	intel_crtc->active = true;
>  
> +	if (!IS_GEN2(dev))
> +		intel_set_cpu_fifo_underrun_reporting(dev, pipe, true);
> +
>  	for_each_encoder_on_crtc(dev, crtc, encoder)
>  		if (encoder->pre_enable)
>  			encoder->pre_enable(encoder);
> @@ -4576,13 +4580,22 @@ static void i9xx_crtc_enable(struct drm_crtc *crtc)
>  
>  	intel_update_watermarks(crtc);
>  	intel_enable_pipe(intel_crtc);
> -	intel_set_cpu_fifo_underrun_reporting(dev, pipe, true);
>  
>  	for_each_encoder_on_crtc(dev, crtc, encoder)
>  		encoder->enable(encoder);
>  
>  	intel_crtc_enable_planes(crtc);
>  
> +	/*
> +	 * Gen2 reports pipe underruns whenever all planes are disabled.
> +	 * So don't enable underrun reporting before at least some planes
> +	 * are enabled.
> +	 * FIXME: Need to fix the logic to work when we turn off all planes
> +	 * but leave the pipe running.
> +	 */
> +	if (IS_GEN2(dev))
> +		intel_set_cpu_fifo_underrun_reporting(dev, pipe, true);

I guess we should do this as part of the nuclear pageflip code iff all
planes are off. But for now this looks good enough imo.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch