pan/midgard: Set r1.w magic

I'm honestly unsure what this is for, but it's needed on MFBD systems
for unknown reasons, at least when MRT is actually in use and then
sometimes without MRT (it fixes a blend shader issue on T760?)

Signed-off-by: Alyssa Rosenzweig <[email protected]>
Reviewed-by: Tomeu Visoso <[email protected]>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/panfrost/midgard/midgard_ra.c b/src/panfrost/midgard/midgard_ra.c
index 749df2efb67..c5c77790e7c 100644
--- a/src/panfrost/midgard/midgard_ra.c
+++ b/src/panfrost/midgard/midgard_ra.c
@@ -524,7 +524,7 @@ allocate_registers(compiler_context *ctx, bool *spilled)
                 assert(check_read_class(l->class, ins->type, ins->src[2]));
         }
 
-        /* Mark writeout to r0, render target to r1.z */
+        /* Mark writeout to r0, render target to r1.z, unknown to r1.w */
         mir_foreach_instr_global(ctx, ins) {
                 if (!(ins->compact_branch && ins->writeout)) continue;
 
@@ -533,6 +533,9 @@ allocate_registers(compiler_context *ctx, bool *spilled)
 
                 if (ins->src[1] < ctx->temp_count)
                         l->solutions[ins->src[1]] = (16 * 1) + COMPONENT_Z * 4;
+
+                if (ins->src[2] < ctx->temp_count)
+                        l->solutions[ins->src[2]] = (16 * 1) + COMPONENT_W * 4;
         }
         
         mir_compute_interference(ctx, l);