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drm/i915: Clear the vblank status bit before polling for the next vblank

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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>
This commit is contained in:
Chris Wilson 2010-09-05 20:25:43 +01:00
parent 4f233eff6f
commit 300387c0b5
1 changed files with 16 additions and 0 deletions
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16
drivers/gpu/drm/i915/intel_display.c
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@ -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),