[Intel-gfx] [PATCH 08/13] drm/i915: FORCE_RESTORE for gen8 semaphores

[Ben Widawsky]

Implement the note indicated in the bspec.

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 2b0598e..bb84be8 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -659,6 +659,15 @@ static int do_switch(struct intel_ring_buffer *ring,
 	if (!to->is_initialized || is_default_context(to))
 		hw_flags |= MI_RESTORE_INHIBIT;
 
+	/* When SW intends to use semaphore signaling between Command streamers,
+	 * it must avoid lite restores in HW by programming "Force Restore" bit
+	 * to ‘1’ in context descriptor during context submission
+	 *
+	 * XXX: is this really needed for ringbuffer mode?
+	 */
+	if (IS_GEN8(ring->dev) && i915_semaphore_is_enabled(ring->dev))
+		hw_flags |= MI_FORCE_RESTORE;
+
 	ret = mi_set_context(ring, to, hw_flags);
 	if (ret)
 		goto unpin_out;
-- 
1.8.5.3