[Intel-gfx] [PATCH 3/4] drm/i915: Add a breadcrumb

[Ben Widawsky]

Getting the watchdog interrupt is great, but knowing the exact batch the
watchdog fired on is even better. There are other ways to do this
without the watchdog, but having the watchdog makes it quite simple.

The idea is to simply emit the seqno before the batchbuffer begins
running, and if the watchdog fires we can read back the location where
the seqno was emitted to see the batchbuffer which hangs.

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +++++-
 drivers/gpu/drm/i915/intel_ringbuffer.h | 3 +++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 82bd0cd..39c6f8e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1332,7 +1332,7 @@ gen6_ring_dispatch_execbuffer(struct intel_ring_buffer *ring,
 {
 	int ret;
 
-	ret = intel_ring_begin(ring, 14);
+	ret = intel_ring_begin(ring, 18);
 	if (ret)
 		return ret;
 
@@ -1345,6 +1345,10 @@ gen6_ring_dispatch_execbuffer(struct intel_ring_buffer *ring,
 	intel_ring_emit(ring, 0);
 
 	/* add breadcrumb here */
+	intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
+	intel_ring_emit(ring, (I915_GEM_WATCHDOG_CRUMB_RCS + ring->id) << MI_STORE_DWORD_INDEX_SHIFT);
+	intel_ring_emit(ring, i915_gem_next_request_seqno(ring));
+	intel_ring_emit(ring, MI_NOOP);
 
 	intel_ring_emit(ring, MI_BATCH_BUFFER_START | MI_BATCH_NON_SECURE_I965);
 	/* bit0-7 is the length on GEN6+ */
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 1d3c81f..73de086 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -183,6 +183,9 @@ intel_read_status_page(struct intel_ring_buffer *ring,
  * The area from dword 0x20 to 0x3ff is available for driver usage.
  */
 #define I915_GEM_HWS_INDEX		0x20
+#define I915_GEM_WATCHDOG_CRUMB_RCS	0x21
+#define I915_GEM_WATCHDOG_CRUMB_VCS	0x22
+#define I915_GEM_WATCHDOG_CRUMB_BCS	0x23
 
 void intel_cleanup_ring_buffer(struct intel_ring_buffer *ring);
 
-- 
1.7.11.2