[PATCH 3/3] drm/i915: close rps work vs. rps disable races

[Daniel Vetter <daniel.vetter@ffwll.ch>]

The rps disabling code wasn't properly cancelling outstanding work
items. Also add a comment that explains why we're not racing with
the work item, that could again unmask interrupts.

This also fixes a bug on module unload because nothing was properly
syncing up with that work item, possibly leading to it being run after
freeing dev_priv or removing the module code.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_display.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 56a8554..ccd4600 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7483,10 +7483,16 @@ void gen6_disable_rps(struct drm_device *dev)
 
 	I915_WRITE(GEN6_RPNSWREQ, 1 << 31);
 	I915_WRITE(GEN6_PMINTRMSK, 0xffffffff);
-	I915_WRITE(GEN6_PMIER, 0);
+	/* Complete PM interrupt masking here doesn't race with the rps work
+	 * item again unmasking PM interrupts because that is using PMIMR
+	 * (logically sitting atop of PMINTRMSK) to mask interrupts. */
+	cancel_work_sync(&dev_priv->rps_work);
 
+	/* Clear PMIMR and dev_priv->pm_iir in case outstanding work gets
+	 * cancelled before having run. */
 	spin_lock_irq(&dev_priv->rps_lock);
 	dev_priv->pm_iir = 0;
+	I915_WRITE(GEN6_PMIER, 0);
 	spin_unlock_irq(&dev_priv->rps_lock);
 
 	I915_WRITE(GEN6_PMIIR, I915_READ(GEN6_PMIIR));
-- 
1.7.6