[Intel-gfx] [PATCH] drm/i915: Use LRI to update the semaphore registers

[Chris Wilson]

The bspec was recently updated to remove the ability to update the
semaphore using the MI_SEMAPHORE_BOX command, the ability to wait upon
the semaphore value remained. Instead the advice is to update the
register using the MI_LOAD_REGISTER_IMM command. In cursory testing,
semaphores continue to function - the question is whether this fixes
some of the deadlocks where the semaphore registers contained stale
values?

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Daniel J Blueman <daniel at quora.org>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index ee4abc5..dd2e7db 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -554,12 +554,9 @@ update_mboxes(struct intel_ring_buffer *ring,
 	    u32 seqno,
 	    u32 mmio_offset)
 {
-	intel_ring_emit(ring, MI_SEMAPHORE_MBOX |
-			      MI_SEMAPHORE_GLOBAL_GTT |
-			      MI_SEMAPHORE_REGISTER |
-			      MI_SEMAPHORE_UPDATE);
-	intel_ring_emit(ring, seqno);
+	intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(1));
 	intel_ring_emit(ring, mmio_offset);
+	intel_ring_emit(ring, seqno);
 }
 
 /**
-- 
1.7.10.4