[Intel-gfx] [PATCH] drm/i915: Eliminate race from gen2/3 page flip interrupt handling

[Paul Menzel]

Am Montag, den 18.02.2013, 13:57 +0200 schrieb ville.syrjala at linux.intel.com:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> If the interrupt handler were to process a previous vblank interrupt and
> the following flip pending interrupt at the same time, the page flip
> would be complete too soon.

»would complete« or »would be complete*d*«

> To eliminate this race check the live pending flip status from the ISR
> register before finishing the page flip.

Could this be tested somehow? Could a test case be written for this?

> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 9fde49a..3de570c 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2284,8 +2284,11 @@ static irqreturn_t i8xx_irq_handler(int irq, void *arg)
>  		    drm_handle_vblank(dev, 0)) {
>  			if (iir & I915_DISPLAY_PLANE_A_FLIP_PENDING_INTERRUPT) {
>  				intel_prepare_page_flip(dev, 0);
> -				intel_finish_page_flip(dev, 0);
> -				flip_mask &= ~I915_DISPLAY_PLANE_A_FLIP_PENDING_INTERRUPT;
> +
> +				if ((I915_READ16(ISR) & I915_DISPLAY_PLANE_A_FLIP_PENDING_INTERRUPT) == 0) {
> +					intel_finish_page_flip(dev, 0);
> +					flip_mask &= ~I915_DISPLAY_PLANE_A_FLIP_PENDING_INTERRUPT;
> +				}
>  			}
>  		}
>  
> @@ -2293,8 +2296,11 @@ static irqreturn_t i8xx_irq_handler(int irq, void *arg)
>  		    drm_handle_vblank(dev, 1)) {
>  			if (iir & I915_DISPLAY_PLANE_B_FLIP_PENDING_INTERRUPT) {
>  				intel_prepare_page_flip(dev, 1);
> -				intel_finish_page_flip(dev, 1);
> -				flip_mask &= ~I915_DISPLAY_PLANE_B_FLIP_PENDING_INTERRUPT;
> +
> +				if ((I915_READ16(ISR) & I915_DISPLAY_PLANE_B_FLIP_PENDING_INTERRUPT) == 0) {
> +					intel_finish_page_flip(dev, 1);
> +					flip_mask &= ~I915_DISPLAY_PLANE_B_FLIP_PENDING_INTERRUPT;
> +				}
>  			}
>  		}
>  
> @@ -2491,8 +2497,11 @@ static irqreturn_t i915_irq_handler(int irq, void *arg)
>  			    drm_handle_vblank(dev, pipe)) {
>  				if (iir & flip[plane]) {
>  					intel_prepare_page_flip(dev, plane);
> -					intel_finish_page_flip(dev, pipe);
> -					flip_mask &= ~flip[plane];
> +
> +					if ((I915_READ(ISR) & flip[plane]) == 0) {

Why not `I915_READ16`?

> +						intel_finish_page_flip(dev, pipe);
> +						flip_mask &= ~flip[plane];
> +					}
>  				}
>  			}


Thanks,

Paul
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