An interesting snippet from Sandybridge's prm:
"Although a Ring Buffer can be enabled in the non-empty state, it must
not be disabled unless it is empty. Attempting to disable a Ring Buffer
in the non-empty state is UNDEFINED."
Let's avoid the undefined behaviour as we disable the rings prior to
reset and resume.
v2: Tell HEAD to catch up to TAIL (empty ring) first, then reset both to
0 (supposedly while stopped).
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
---
More investigatory stabs at the shards.
-Chris
---
drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +++++-
drivers/gpu/drm/i915/intel_uncore.c | 6 +++++-
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 05e01446b00b..47fadf8da84e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -480,10 +480,14 @@ static bool stop_ring(struct intel_engine_cs *engine)
}
}
- I915_WRITE_CTL(engine, 0);
+ I915_WRITE_HEAD(engine, I915_READ_TAIL(engine));
+
I915_WRITE_HEAD(engine, 0);
I915_WRITE_TAIL(engine, 0);
+ /* The ring must be empty before it is disabled */
+ I915_WRITE_CTL(engine, 0);
+
return (I915_READ_HEAD(engine) & HEAD_ADDR) == 0;
}
diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 20e3c65c0999..96ee6b2754be 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1387,10 +1387,14 @@ static void gen3_stop_engine(struct intel_engine_cs *engine)
DRM_DEBUG_DRIVER("%s: timed out on STOP_RING\n",
engine->name);
- I915_WRITE_FW(RING_CTL(base), 0);
+ I915_WRITE_FW(RING_HEAD(base), I915_READ_FW(RING_TAIL(base)));
+
I915_WRITE_FW(RING_HEAD(base), 0);
I915_WRITE_FW(RING_TAIL(base), 0);
+ /* The ring must be empty before it is disabled */
+ I915_WRITE_FW(RING_CTL(base), 0);
+
/* Check acts as a post */
if (I915_READ_FW(RING_HEAD(base)) != 0)
DRM_DEBUG_DRIVER("%s: ring head not parked\n",
--
2.15.0.rc2
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