[Intel-gfx] [PATCH 6/6] drm/i915: Kick start the rings

[Chris Wilson]

On g4x, we have an issue where the register write to setup the rings do
not always take. However, it appears that the current check also passes
only by chance, a second reading of the register returns a different
broekn value - but the GPU appears to function. Based on that
observation, lets try feeding a nop into the ring and seeing if it
advances as part of our startup sanity checks.

References: https://bugs.freedesktop.org/show_bug.cgi?id=76554
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index a8c73a0d935d..bc52645fa8d5 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -514,10 +514,14 @@ static int init_ring_common(struct intel_ring_buffer *ring)
 			((ring->size - PAGE_SIZE) & RING_NR_PAGES)
 			| RING_VALID);
 
+	iowrite32(MI_NOOP, ring->virtual_start + 0);
+	iowrite32(MI_NOOP, ring->virtual_start + 4);
+	ring->write_tail(ring, 8);
+
 	/* If the head is still not zero, the ring is dead */
 	if (wait_for((I915_READ_CTL(ring) & RING_VALID) != 0 &&
 		     I915_READ_START(ring) == i915_gem_obj_ggtt_offset(obj) &&
-		     (I915_READ_HEAD(ring) & HEAD_ADDR) == 0, 50)) {
+		     (I915_READ_HEAD(ring) & HEAD_ADDR) == 8, 50)) {
 		DRM_ERROR("%s initialization failed "
 			  "ctl %08x (valid? %d) head %08x tail %08x start %08x [expected %08lx]\n",
 			  ring->name,
-- 
1.9.1