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Date: Mon, 15 Sep 2014 15:09:40 -0700 From: Kamal Mostafa <kamal@...onical.com> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...ts.ubuntu.com Cc: Jiri Kosina <jkosina@...e.cz>, Daniel Vetter <daniel.vetter@...ll.ch>, Kamal Mostafa <kamal@...onical.com> Subject: [PATCH 3.13 170/187] drm/i915: read HEAD register back in init_ring_common() to enforce ordering 3.13.11.7 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiri Kosina <jkosina@...e.cz> commit ece4a17d237a79f63fbfaf3f724a12b6d500555c upstream. Withtout this, ring initialization fails reliabily during resume with [drm:init_ring_common] *ERROR* render ring initialization failed ctl 0001f001 head ffffff8804 tail 00000000 start 000e4000 This is not a complete fix, but it is verified to make the ring initialization failures during resume much less likely. We were not able to root-cause this bug (likely HW-specific to Gen4 chips) yet. This is therefore used as a ducttape before problem is fully understood and proper fix created, so that people don't suffer from completely unusable systems in the meantime. The discussion and debugging is happening at https://bugs.freedesktop.org/show_bug.cgi?id=76554 Signed-off-by: Jiri Kosina <jkosina@...e.cz> Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch> Signed-off-by: Kamal Mostafa <kamal@...onical.com> --- drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c index 53f5458..dfb8546 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -473,6 +473,9 @@ static int init_ring_common(struct intel_ring_buffer *ring) } } + /* Enforce ordering by reading HEAD register back */ + I915_READ_HEAD(ring); + /* Initialize the ring. This must happen _after_ we've cleared the ring * registers with the above sequence (the readback of the HEAD registers * also enforces ordering), otherwise the hw might lose the new ring -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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