From 300387c0b57d75e5218e2881d6ad2720657a8bcf Mon Sep 17 00:00:00 2001 From: Chris Wilson <chris@chris-wilson.co.uk> Date: Sun, 5 Sep 2010 20:25:43 +0100 Subject: [PATCH] drm/i915: Clear the vblank status bit before polling for the next vblank The vblank status bit is a sticky bit that must be cleared with a write of '1' prior to polling for the next vblank. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Tested-by: Sitsofe Wheeler <sitsofe@yahoo.com> jbarnes: I'd still rather see a lock, but I think you're right that we don't generally wait in code that needs not to miss an interrupt. Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org> --- drivers/gpu/drm/i915/intel_display.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 11a3394f5fe1..3fc767bcbaa0 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -990,6 +990,22 @@ void intel_wait_for_vblank(struct drm_device *dev, int pipe) struct drm_i915_private *dev_priv = dev->dev_private; int pipestat_reg = (pipe == 0 ? PIPEASTAT : PIPEBSTAT); + /* Clear existing vblank status. Note this will clear any other + * sticky status fields as well. + * + * This races with i915_driver_irq_handler() with the result + * that either function could miss a vblank event. Here it is not + * fatal, as we will either wait upon the next vblank interrupt or + * timeout. Generally speaking intel_wait_for_vblank() is only + * called during modeset at which time the GPU should be idle and + * should *not* be performing page flips and thus not waiting on + * vblanks... + * Currently, the result of us stealing a vblank from the irq + * handler is that a single frame will be skipped during swapbuffers. + */ + I915_WRITE(pipestat_reg, + I915_READ(pipestat_reg) | PIPE_VBLANK_INTERRUPT_STATUS); + /* Wait for vblank interrupt bit to set */ if (wait_for((I915_READ(pipestat_reg) & PIPE_VBLANK_INTERRUPT_STATUS), -- GitLab