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    Subject[ 43/55] drm/i915: Avoid a double-read of PCH_IIR during interrupt handling
    3.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Chris Wilson <chris@chris-wilson.co.uk>

    commit 9adab8b5a7fde248504f484e197589f3e3c922e2 upstream.

    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>
    Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/i915/i915_irq.c | 9 +++------
    1 file changed, 3 insertions(+), 6 deletions(-)

    --- a/drivers/gpu/drm/i915/i915_irq.c
    +++ b/drivers/gpu/drm/i915/i915_irq.c
    @@ -422,14 +422,11 @@ static void gen6_pm_rps_work(struct work
    mutex_unlock(&dev_priv->dev->struct_mutex);
    }

    -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) >>
    @@ -527,7 +524,7 @@ static irqreturn_t ivybridge_irq_handler
    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) {
    @@ -626,7 +623,7 @@ static irqreturn_t ironlake_irq_handler(
    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) {



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