Re: [PATCH] drm/i915: Force vblanks around evasion when i915.watermark_test is set.

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Jun 09, 2016 at 01:36:50PM +0200, Maarten Lankhorst wrote:
> This will make it more likely that intermediary watermarks cause fifo
> underruns, which is useful when writing watermark specific tests,
> to make it more likely to trigger FIFO underruns in intermediary watermarks.

That's surprising ... with the vblank_wait added you're pretty much
guaranteed to never hit the evasion case. Note that the vblank evasion
code also just does a vblank wait if it detects a possible collision.

Given that I'd have assumed that this simply slows down atomic flips,
which is probably not what we want for testing all. Does this really help?
Any ideas why?
-Daniel

> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_params.c   | 1 +
>  drivers/gpu/drm/i915/i915_params.h   | 1 +
>  drivers/gpu/drm/i915/intel_display.c | 6 ++++++
>  3 files changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 5e18cf9f754d..297d1cd53b15 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -45,6 +45,7 @@ struct i915_params i915 __read_mostly = {
>  	.fastboot = 0,
>  	.prefault_disable = 0,
>  	.load_detect_test = 0,
> +	.watermark_test = 0,
>  	.reset = true,
>  	.invert_brightness = 0,
>  	.disable_display = 0,
> diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> index 1323261a0cdd..91f976c6bac6 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -57,6 +57,7 @@ struct i915_params {
>  	bool fastboot;
>  	bool prefault_disable;
>  	bool load_detect_test;
> +	bool watermark_test;
>  	bool reset;
>  	bool disable_display;
>  	bool verbose_state_checks;
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 8bb8d36f5cb9..9dcf304c7b1f 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -14184,6 +14184,9 @@ static void intel_begin_crtc_commit(struct drm_crtc *crtc,
>  		to_intel_crtc_state(old_crtc_state);
>  	bool modeset = needs_modeset(crtc->state);
>  
> +	if (i915.watermark_test)
> +		intel_wait_for_vblank(dev, intel_crtc->pipe);
> +
>  	/* Perform vblank evasion around commit operation */
>  	intel_pipe_update_start(intel_crtc);
>  
> @@ -14207,6 +14210,9 @@ static void intel_finish_crtc_commit(struct drm_crtc *crtc,
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  
>  	intel_pipe_update_end(intel_crtc, NULL);
> +
> +	if (i915.watermark_test)
> +		intel_wait_for_vblank(crtc->dev, intel_crtc->pipe);
>  }
>  
>  /**
> -- 
> 2.5.5
> 
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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