[Intel-gfx] [PATCH v2 4/4] drm/i915/chv: Ack interrupts before handling them (CHV)

[oscar.mateo at intel.com]

From: Oscar Mateo <oscar.mateo at intel.com>

Otherwise, we might receive a new interrupt before we have time to
ack the first one, eventually missing it.

Without an atomic XCHG operation with mmio space, this patch merely
reduces the window in which we can miss an interrupt (especially when
you consider how heavyweight the I915_READ/I915_WRITE operations are).

Notice that, before clearing a port-sourced interrupt in the IIR, the
corresponding interrupt source status in the PORT_HOTPLUG_STAT must be
cleared.

Spotted by Bob Beckett <robert.beckett at intel.com>.

v2:
- Add warning to commit message and comments to the code as per Chris
  Wilson's request.
- Imre Deak pointed out that the pipe underrun flag might not be signaled
  in IIR, so do not make valleyview_pipestat_irq_handler depend on it.

Signed-off-by: Oscar Mateo <oscar.mateo at intel.com>
---
 drivers/gpu/drm/i915/i915_irq.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 69c24b0..630b7fc 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1889,27 +1889,33 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg)
 	irqreturn_t ret = IRQ_NONE;
 
 	for (;;) {
+		/* Find the source(s) of the interrupt and clear the IIR
+		 * before processing */
 		master_ctl = I915_READ(GEN8_MASTER_IRQ) & ~GEN8_MASTER_IRQ_CONTROL;
 		iir = I915_READ(VLV_IIR);
 
 		if (master_ctl == 0 && iir == 0)
 			break;
 
+		ret = IRQ_HANDLED;
+
 		I915_WRITE(GEN8_MASTER_IRQ, 0);
 
-		gen8_gt_irq_handler(dev, dev_priv, master_ctl);
+		if (iir) {
+			/* Consume port before clearing IIR or we'll miss events */
+			if (iir & I915_DISPLAY_PORT_INTERRUPT)
+				i9xx_hpd_irq_handler(dev);
+			I915_WRITE(VLV_IIR, iir);
+		}
 
+		/* Call regardless, as some status bits might not be
+		 * signalled in iir */
 		valleyview_pipestat_irq_handler(dev, iir);
 
-		/* Consume port.  Then clear IIR or we'll miss events */
-		i9xx_hpd_irq_handler(dev);
-
-		I915_WRITE(VLV_IIR, iir);
+		gen8_gt_irq_handler(dev, dev_priv, master_ctl);
 
 		I915_WRITE(GEN8_MASTER_IRQ, DE_MASTER_IRQ_CONTROL);
 		POSTING_READ(GEN8_MASTER_IRQ);
-
-		ret = IRQ_HANDLED;
 	}
 
 	return ret;
-- 
1.9.0