drm/i915: catch gtfifo errors on forcewake_put

This is similar to a patch I wrote several months ago. It's been updated
for the new FORCEWAKE_MT. As recommended by Chris Wilson, use WARN()
instead of DRM_ERROR, so we can get a backtrace.

This shouldn't impact performance too much as the extra register read
can replace the POSTING_READ we had previously.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 189041984aba..d783e2b4c914 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -385,16 +385,27 @@ void gen6_gt_force_wake_get(struct drm_i915_private *dev_priv)
         spin_unlock_irqrestore(&dev_priv->gt_lock, irqflags);
 }
 
+static void gen6_gt_check_fifodbg(struct drm_i915_private *dev_priv)
+{
+        u32 gtfifodbg;
+        gtfifodbg = I915_READ_NOTRACE(GTFIFODBG);
+        if (WARN(gtfifodbg & GT_FIFO_CPU_ERROR_MASK,
+             "MMIO read or write has been dropped %x\n", gtfifodbg))
+                I915_WRITE_NOTRACE(GTFIFODBG, GT_FIFO_CPU_ERROR_MASK);
+}
+
 void __gen6_gt_force_wake_put(struct drm_i915_private *dev_priv)
 {
         I915_WRITE_NOTRACE(FORCEWAKE, 0);
-        POSTING_READ(FORCEWAKE);
+        /* The below doubles as a POSTING_READ */
+        gen6_gt_check_fifodbg(dev_priv);
 }
 
 void __gen6_gt_force_wake_mt_put(struct drm_i915_private *dev_priv)
 {
         I915_WRITE_NOTRACE(FORCEWAKE_MT, (1<<16) | 0);
-        POSTING_READ(FORCEWAKE_MT);
+        /* The below doubles as a POSTING_READ */
+        gen6_gt_check_fifodbg(dev_priv);
 }
 
 /*