From a4acb8d0933f89eca6c26c2d3da39e6294e4fb98 Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Thu, 7 Aug 2014 14:04:09 +0200 Subject: [PATCH] drm/i915: read HEAD register back in init_ring_common() to enforce ordering 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 Signed-off-by: Jiri Kosina --- 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 279488a..7add7ee 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -517,6 +517,9 @@ static int init_ring_common(struct intel_engine_cs *ring) else ring_setup_phys_status_page(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 -- 1.8.5.2