Re: [PATCH 2/6] drm/i915: Don't wait for page flips if there was GPU reset

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jan 29, 2013 at 06:13:34PM +0200, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> If a GPU reset occurs while a page flip has been submitted to the ring,
> the flip will never complete once the ring has been reset.
> 
> The GPU reset can be detected by sampling the reset_counter before the
> flip is submitted, and then while waiting for the flip, the sampled
> counter is compared with the current reset_counter value.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 14 +++++++++++++-
>  drivers/gpu/drm/i915/intel_drv.h     |  3 +++
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 4097118..e348a68 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -2862,10 +2862,12 @@ static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
>  {
>  	struct drm_device *dev = crtc->dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	unsigned long flags;
>  	bool pending;
>  
> -	if (i915_reset_in_progress(&dev_priv->gpu_error))
> +	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> +	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
>  		return false;
>  
>  	spin_lock_irqsave(&dev->event_lock, flags);
> @@ -6912,6 +6914,8 @@ static int intel_gen2_queue_flip(struct drm_device *dev,
>  	if (ret)
>  		goto err_unpin;
>  
> +	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);

Ok no bikeshed about ->reset_counter, but a different one: Why does this
need to be in the per-gen callback? Can't we just grab this before we call
down into these callbacks? Imo races wrt the reset/hang code don't matter
that much as long as we don't wait forever for a pageflip which won't
happen. Hanging the gpu concurrently to pageflipping is undefined anyway
right now ...
-Daniel

> +
>  	/* Can't queue multiple flips, so wait for the previous
>  	 * one to finish before executing the next.
>  	 */
> @@ -6956,6 +6960,8 @@ static int intel_gen3_queue_flip(struct drm_device *dev,
>  	if (ret)
>  		goto err_unpin;
>  
> +	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +
>  	if (intel_crtc->plane)
>  		flip_mask = MI_WAIT_FOR_PLANE_B_FLIP;
>  	else
> @@ -6997,6 +7003,8 @@ static int intel_gen4_queue_flip(struct drm_device *dev,
>  	if (ret)
>  		goto err_unpin;
>  
> +	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +
>  	/* i965+ uses the linear or tiled offsets from the
>  	 * Display Registers (which do not change across a page-flip)
>  	 * so we need only reprogram the base address.
> @@ -7045,6 +7053,8 @@ static int intel_gen6_queue_flip(struct drm_device *dev,
>  	if (ret)
>  		goto err_unpin;
>  
> +	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +
>  	intel_ring_emit(ring, MI_DISPLAY_FLIP |
>  			MI_DISPLAY_FLIP_PLANE(intel_crtc->plane));
>  	intel_ring_emit(ring, fb->pitches[0] | obj->tiling_mode);
> @@ -7111,6 +7121,8 @@ static int intel_gen7_queue_flip(struct drm_device *dev,
>  	if (ret)
>  		goto err_unpin;
>  
> +	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +
>  	intel_ring_emit(ring, MI_DISPLAY_FLIP_I915 | plane_bit);
>  	intel_ring_emit(ring, (fb->pitches[0] | obj->tiling_mode));
>  	intel_ring_emit(ring, obj->gtt_offset + intel_crtc->dspaddr_offset);
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index fcdfe42..a5521d9 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -235,6 +235,9 @@ struct intel_crtc {
>  	/* We can share PLLs across outputs if the timings match */
>  	struct intel_pch_pll *pch_pll;
>  	uint32_t ddi_pll_sel;
> +
> +	/* reset counter value when the last flip was submitted */
> +	unsigned int reset_counter;
>  };
>  
>  struct intel_plane {
> -- 
> 1.7.12.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch