[PATCH 11/24] drm/i915: improve SERR_INT clearing for fifo underrun reporting

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

The current code won't report any fifo underruns on cpt if just one
pipe has fifo underrun reporting disabled. We can't enable the
interrupts, but we can still check the per-transcoder bits and so
report the underrun delayed if:
- We always clear the transcoder's bit (and none of the other bits)
  when enabling.
- We check the transcoder's bit after disabling (to avoid racing with
  the interrupt handler).

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_irq.c | 15 +++++++++++----
 drivers/gpu/drm/i915/i915_reg.h |  1 +
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 685ad84..8627043 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -210,16 +210,23 @@ static void cpt_set_fifo_underrun_reporting(struct drm_device *dev,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
 	if (enable) {
+		I915_WRITE(SERR_INT,
+			   SERR_INT_TRANS_FIFO_UNDERRUN(pch_transcoder));
+
 		if (!cpt_can_enable_serr_int(dev))
 			return;
-
-		I915_WRITE(SERR_INT, SERR_INT_TRANS_A_FIFO_UNDERRUN |
-				     SERR_INT_TRANS_B_FIFO_UNDERRUN |
-				     SERR_INT_TRANS_C_FIFO_UNDERRUN);
 	}
 
 	ibx_display_interrupt_update(dev_priv, SDE_ERROR_CPT,
 				     enable ? SDE_ERROR_CPT : 0);
+
+	if (!enable) {
+		uint32_t tmp = I915_READ(SERR_INT);
+
+		if (tmp & SERR_INT_TRANS_FIFO_UNDERRUN(pch_transcoder))
+			DRM_DEBUG_KMS("uncleared pch fifo underrun on pipe %i\n",
+				      pch_transcoder);
+	}
 }
 
 /**
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index b1fdca9..86e3987 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3880,6 +3880,7 @@
 #define  SERR_INT_TRANS_C_FIFO_UNDERRUN	(1<<6)
 #define  SERR_INT_TRANS_B_FIFO_UNDERRUN	(1<<3)
 #define  SERR_INT_TRANS_A_FIFO_UNDERRUN	(1<<0)
+#define  SERR_INT_TRANS_FIFO_UNDERRUN(pipe)	(1<< (pipe*3))
 
 /* digital port hotplug */
 #define PCH_PORT_HOTPLUG        0xc4030		/* SHOTPLUG_CTL */
-- 
1.8.1.4