[PATCH 05/10] drm/i915: also disable south interrupts when handling them

[Paulo Zanoni <przanoni@gmail.com>]

From: Paulo Zanoni <paulo.r.zanoni@intel.com>

>From the docs:
  "Only the rising edge of the PCH Display interrupt will cause the
  North Display IIR (DEIIR) PCH Display Interrupt even bit to be set,
  so all PCH Display Interrupts, including back to back interrupts,
  must be cleared before a new PCH Display interrupt can cause DEIIR
  to be set".

The current code works fine because we don't get many interrupts, but
if we enable the PCH FIFO underrun interrupts we'll start getting so
many interrupts that at some point new PCH interrupts won't cause
DEIIR to be set.

The initial implementation I tried was to turn the code that checks
SDEIIR into a loop, but we can still get interrupts even after the
loop is done (and before the irq handler finishes), so we have to
either disable the interrupts or mask them. In the end I concluded
that just disabling the PCH interrupts is enough, you don't even need
the loop, so this is what this patch implements. I've tested it and it
passes the 2 "PCH FIFO underrun interrupt storms" I can reproduce:
the "ironlake_crtc_disable" case and the "wrong watermarks" case.

In other words, here's how to reproduce the problem fixed by this
patch:
  1 - Enable PCH FIFO underrun interrupts (SERR_INT on SNB+)
  2 - Boot the machine
  3 - While booting we'll get tons of PCH FIFO underrun interrupts
  4 - Plug a new monitor
  5 - Run xrandr, notice it won't detect the new monitor
  6 - Read SDEIIR and notice it's not 0 while DEIIR is 0

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
 drivers/gpu/drm/i915/i915_irq.c |   16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index f096ad9..500fd65 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -701,7 +701,7 @@ static irqreturn_t ivybridge_irq_handler(int irq, void *arg)
 {
 	struct drm_device *dev = (struct drm_device *) arg;
 	drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
-	u32 de_iir, gt_iir, de_ier, pm_iir;
+	u32 de_iir, gt_iir, de_ier, pm_iir, sde_ier;
 	irqreturn_t ret = IRQ_NONE;
 	int i;
 
@@ -711,6 +711,10 @@ static irqreturn_t ivybridge_irq_handler(int irq, void *arg)
 	de_ier = I915_READ(DEIER);
 	I915_WRITE(DEIER, de_ier & ~DE_MASTER_IRQ_CONTROL);
 
+	sde_ier = I915_READ(SDEIER);
+	I915_WRITE(SDEIER, 0);
+	POSTING_READ(SDEIER);
+
 	gt_iir = I915_READ(GTIIR);
 	if (gt_iir) {
 		snb_gt_irq_handler(dev, dev_priv, gt_iir);
@@ -759,6 +763,8 @@ static irqreturn_t ivybridge_irq_handler(int irq, void *arg)
 
 	I915_WRITE(DEIER, de_ier);
 	POSTING_READ(DEIER);
+	I915_WRITE(SDEIER, sde_ier);
+	POSTING_READ(SDEIER);
 
 	return ret;
 }
@@ -778,7 +784,7 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg)
 	struct drm_device *dev = (struct drm_device *) arg;
 	drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 	int ret = IRQ_NONE;
-	u32 de_iir, gt_iir, de_ier, pm_iir;
+	u32 de_iir, gt_iir, de_ier, pm_iir, sde_ier;
 
 	atomic_inc(&dev_priv->irq_received);
 
@@ -787,6 +793,10 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg)
 	I915_WRITE(DEIER, de_ier & ~DE_MASTER_IRQ_CONTROL);
 	POSTING_READ(DEIER);
 
+	sde_ier = I915_READ(SDEIER);
+	I915_WRITE(SDEIER, 0);
+	POSTING_READ(SDEIER);
+
 	de_iir = I915_READ(DEIIR);
 	gt_iir = I915_READ(GTIIR);
 	pm_iir = I915_READ(GEN6_PMIIR);
@@ -849,6 +859,8 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg)
 done:
 	I915_WRITE(DEIER, de_ier);
 	POSTING_READ(DEIER);
+	I915_WRITE(SDEIER, sde_ier);
+	POSTING_READ(SDEIER);
 
 	return ret;
 }
-- 
1.7.10.4