[Mesa-dev] [PATCH] i965: Implement another VF cache invalidate workaround on Gen8+.

[Kenneth Graunke]

...and provide a better citation for the existing one.

v2:
- Apply the workaround to Gen8 too, as intended (caught by Topi).
- Restructure to add bits instead of an extra flush (based on a similar
  patch by Rafael Antognolli).
---
 src/mesa/drivers/dri/i965/brw_pipe_control.c | 41 ++++++++++++++++++++++------
 1 file changed, 33 insertions(+), 8 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_pipe_control.c b/src/mesa/drivers/dri/i965/brw_pipe_control.c
index 39e8bff7309..c6e7dd15f4c 100644
--- a/src/mesa/drivers/dri/i965/brw_pipe_control.c
+++ b/src/mesa/drivers/dri/i965/brw_pipe_control.c
@@ -119,14 +119,39 @@ brw_emit_pipe_control(struct brw_context *brw, uint32_t flags,
       if (devinfo->gen == 8)
          gen8_add_cs_stall_workaround_bits(&flags);
 
-      if (devinfo->gen == 9 &&
-          (flags & PIPE_CONTROL_VF_CACHE_INVALIDATE)) {
-         /* Hardware workaround: SKL
-          *
-          * Emit Pipe Control with all bits set to zero before emitting
-          * a Pipe Control with VF Cache Invalidate set.
-          */
-         brw_emit_pipe_control_flush(brw, 0);
+      if (flags & PIPE_CONTROL_VF_CACHE_INVALIDATE) {
+         if (devinfo->gen == 9) {
+            /* The PIPE_CONTROL "VF Cache Invalidation Enable" bit description
+             * lists several workarounds:
+             *
+             *    "Project: SKL, KBL, BXT
+             *
+             *     If the VF Cache Invalidation Enable is set to a 1 in a
+             *     PIPE_CONTROL, a separate Null PIPE_CONTROL, all bitfields
+             *     sets to 0, with the VF Cache Invalidation Enable set to 0
+             *     needs to be sent prior to the PIPE_CONTROL with VF Cache
+             *     Invalidation Enable set to a 1."
+             */
+            brw_emit_pipe_control_flush(brw, 0);
+         }
+
+         if (devinfo->gen >= 8) {
+            /* THE PIPE_CONTROL "VF Cache Invalidation Enable" docs continue:
+             *
+             *    "Project: BDW+
+             *
+             *     When VF Cache Invalidate is set “Post Sync Operation” must
+             *     be enabled to “Write Immediate Data” or “Write PS Depth
+             *     Count” or “Write Timestamp”."
+             *
+             * If there's a BO, we're already doing some kind of write.
+             * If not, add a write to the workaround BO.
+             */
+            if (!bo) {
+               flags |= PIPE_CONTROL_WRITE_IMMEDIATE;
+               bo = brw->workaround_bo;
+            }
+         }
       }
 
       if (devinfo->gen == 10)
-- 
2.15.0