[Mesa-dev] [PATCH] i965/gen8: Use HALIGN_16 for single sample mcs buffers

[Ben Widawsky]

The original code meant to do this, but was only checking num_samples == 1 to
figure out if a surface was fast clear capable. However, we can allocate single
sample miptrees with num_samples == 0 (when it's an internally created buffer).

This fixes a bunch of the piglit tests on gen8. Other gens should have been
fine.

Here is the order of events that allowed this to slip through:
t0: I wrote halign patches and tested them. These alignment assertions are for
   gen8 fast clear surfaces, basically.
t1: I pushed bogus perf patch which made fast clears never happen
t2: Reworked halign patches based on Chad's feedback and introduced the bug this
   patch fixes.
t2.5: I tested reworked patches, but assertion wasn't hit because of t1.
t3. Matt fixed issue in t1 which made fast clears happen here:
commit 22af95af8316f2888a3935cdf774ff0997b3dd42
Author: Matt Turner <mattst88 at gmail.com>
Date:   Thu Jun 18 16:14:50 2015 -0700

    i965: Add missing braces around if-statement.

This logic should match that of the v1 of my halign patch series.

Cc: Kenneth Graunke <kenneth at whitecape.org>
Cc: Matt Turner <mattst88 at gmail.com>
Reported-by: Kenneth Graunke <kenneth at whitecape.org>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 src/mesa/drivers/dri/i965/intel_mipmap_tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
index 80c52f2..6aa969a 100644
--- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
+++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
@@ -501,7 +501,7 @@ intel_miptree_create_layout(struct brw_context *brw,
     *  6   |      ?         |        ?
     */
    if (intel_miptree_is_fast_clear_capable(brw, mt)) {
-      if (brw->gen >= 9 || (brw->gen == 8 && num_samples == 1))
+      if (brw->gen >= 9 || (brw->gen == 8 && num_samples <= 1))
          layout_flags |= MIPTREE_LAYOUT_FORCE_HALIGN16;
    } else if (brw->gen >= 9 && num_samples > 1) {
       layout_flags |= MIPTREE_LAYOUT_FORCE_HALIGN16;
-- 
2.4.4