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drm/i915: Be paranoid and post the writes to stop the rings 

Although the mmio are uncached and so should be flushed on every write,
be paranoid and do a mmio read after setting the ring head/tail to be
sure they have taken effect before moving on.

v2: post tail to be pleasing to the eye

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180208072800.595-1-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
This commit is contained in:
Chris Wilson 2018-02-08 07:28:00 +00:00
parent 0d73e7a095
commit bc8f2f5db9
1 changed files with 2 additions and 0 deletions
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2
drivers/gpu/drm/i915/intel_uncore.c
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@ -1522,9 +1522,11 @@ static void gen3_stop_engine(struct intel_engine_cs *engine)
engine->name);
I915_WRITE_FW(RING_HEAD(base), I915_READ_FW(RING_TAIL(base)));
POSTING_READ_FW(RING_HEAD(base)); /* paranoia */
I915_WRITE_FW(RING_HEAD(base), 0);
I915_WRITE_FW(RING_TAIL(base), 0);
POSTING_READ_FW(RING_TAIL(base));
/* The ring must be empty before it is disabled */
I915_WRITE_FW(RING_CTL(base), 0);