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

[Ben Widawsky]

This appears to not actually be needed on the current code. Just putting
it on the ML so we can point bug reports at it later.

As pointed out by Ville, the current code is "broken" since we do
FORCE_RESTORE, and RESTORE_INHIBIT on the same dword. Anecdotally, this
seems fine.

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index f77b4c1..aa82fb4 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -661,6 +661,13 @@ static int do_switch(struct intel_ring_buffer *ring,
 	if (!to->is_initialized || i915_gem_context_is_default(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
+	 */
+	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;
-- 
1.9.2