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drm/i915: Empty the ring before disabling

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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@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171027094311.30380-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2017-10-27 10:43:11 +01:00
parent e6ed2a1b99
commit 11caf5517c
2 changed files with 10 additions and 2 deletions
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6
drivers/gpu/drm/i915/intel_ringbuffer.c
View File

@ -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;
}

6
drivers/gpu/drm/i915/intel_uncore.c
View File

@ -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",