[Intel-gfx] [PATCH 2/2] drm/i915: catch gtfifo errors on forcewake_put

[Ben Widawsky]

This is similar to a patch I wrote several months ago. It's been updated
for the new FORCEWAKE_MT, and it also no longer clears the debug
register as it may be helpful to get that for the error state.  Also
recommended by Chris Wilson, use WARN() instead of DRM_ERROR, so we can
get a backtrace.

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_drv.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 1658cfd..3f88ca8 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -381,12 +381,18 @@ void gen6_gt_force_wake_get(struct drm_i915_private *dev_priv)
 
 void __gen6_gt_force_wake_put(struct drm_i915_private *dev_priv)
 {
+	u32 gtfifodbg = I915_READ(GTFIFODBG);
+	WARN(gtfifodbg & GT_FIFO_CPU_ERROR_MASK,
+	     "MMIO read or write has been dropped %x\n", gtfifodbg);
 	I915_WRITE_NOTRACE(FORCEWAKE, 0);
 	POSTING_READ(FORCEWAKE);
 }
 
 void __gen6_gt_force_wake_mt_put(struct drm_i915_private *dev_priv)
 {
+	u32 gtfifodbg = I915_READ(GTFIFODBG);
+	WARN(gtfifodbg & GT_FIFO_CPU_ERROR_MASK,
+	     "MMIO read or write has been dropped %x\n", gtfifodbg);
 	I915_WRITE_NOTRACE(FORCEWAKE_MT, (1<<16) | 0);
 	POSTING_READ(FORCEWAKE_MT);
 }
-- 
1.7.9