From: Ville Syrjälä Date: Tue, 19 Feb 2013 13:16:38 +0000 (+0200) Subject: drm/i915: Eliminate race from gen2/3 page flip interrupt handling X-Git-Tag: firefly_0821_release~3680^2~443^2~82^2~64 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=5e2032d47ac9b67e671bd855c5e68005190954da;p=firefly-linux-kernel-4.4.55.git drm/i915: Eliminate race from gen2/3 page flip interrupt handling 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 completed too soon. To eliminate this race, check the live pending flip status from the ISR register before finishing the page flip. v2: Added a comment explaining the logic (by Chris Wilson) v3: Fix a typo in the comment Reviewed-by: Chris Wilson Tested-by: Chris Wilson Signed-off-by: Ville Syrjälä Signed-off-by: Daniel Vetter --- diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index 9fde49a29999..6488249477db 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 +2497,17 @@ 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]; + + /* We detect FlipDone by looking for the change in PendingFlip from '1' + * to '0' on the following vblank, i.e. IIR has the Pendingflip + * asserted following the MI_DISPLAY_FLIP, but ISR is deasserted, hence + * the flip is completed (no longer pending). Since this doesn't raise an + * interrupt per se, we watch for the change at vblank. + */ + if ((I915_READ(ISR) & flip[plane]) == 0) { + intel_finish_page_flip(dev, pipe); + flip_mask &= ~flip[plane]; + } } }