[PATCH 1/2] drm/i915: Avoid a double-read of PCH_IIR during interrupt handling

Chris Wilson
2012-05-09T20:46:27Z

Currently the code re-reads PCH_IIR during the hotplug interrupt
processing. Not only is this a wasted read, but introduces a potential
for handling a spurious interrupt as we then may not clear all the
interrupts processed (since the re-read IIR may contains more interrupts
asserted than we clear using the result of the original read).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: stable@kernel.org
---
drivers/gpu/drm/i915/i915_irq.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b4999b5..14943ba 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -533,14 +533,11 @@ out:
return ret;
}

-static void pch_irq_handler(struct drm_device *dev)
+static void pch_irq_handler(struct drm_device *dev, u32 pch_iir)
{
drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
- u32 pch_iir;
int pipe;

- pch_iir = I915_READ(SDEIIR);
-
if (pch_iir & SDE_AUDIO_POWER_MASK)
DRM_DEBUG_DRIVER("PCH audio power change on port %d\n",
(pch_iir & SDE_AUDIO_POWER_MASK) >>
@@ -633,7 +630,7 @@ static irqreturn_t ivybridge_irq_handler(DRM_IRQ_ARGS)
if (de_iir & DE_PCH_EVENT_IVB) {
if (pch_iir & SDE_HOTPLUG_MASK_CPT)
queue_work(dev_priv->wq, &dev_priv->hotplug_work);
- pch_irq_handler(dev);
+ pch_irq_handler(dev, pch_iir);
}

if (pm_iir & GEN6_PM_DEFERRED_EVENTS)
@@ -721,7 +718,7 @@ static irqreturn_t ironlake_irq_handler(DRM_IRQ_ARGS)
if (de_iir & DE_PCH_EVENT) {
if (pch_iir & hotplug_mask)
queue_work(dev_priv->wq, &dev_priv->hotplug_work);
- pch_irq_handler(dev);
+ pch_irq_handler(dev, pch_iir);
}

if (de_iir & DE_PCU_EVENT) {
--
1.7.10