[Mesa-dev] [PATCH 1/6] i965: Kill y_or_x variable in miptree tiling selection

[Ben Widawsky]

NOTE: The commit message is retained for posterity, however there were some
changes in the code since the patch was originally written that may make the old
commit message false. Starting with v4 is actually much simpler than the
original change.

This patch is needed to help keep some of the churn down later in the series
(IIRC)

v3: Rebased + redone on top of the layout flags + tiling patch.

Original commit message:

IMHO, intel_miptree_choose_tiling() is an unfortunate incarnation because it
conflates what is permitted vs. what is desirable. This makes doing any sort of
"fallback" operations after the fact somewhat kludgey.

The original code basically says:
"if we requested x XOR y-tiled, and the region > aperture; then try to x-tiled"

Better would be:
"if we *received* x OR y-tiled, and the region > aperture; then try to x-tiled"

Optimally it is:
"if we can use either x OR y-tiled and got y-tiled, and the region > aperture; then try
x tiled"

This patch actually addresses two potential issues:
1.  As far as I can tell, drm_intel_gem_bo_alloc_tiled() which is invariably
called, can potentially change the tiling type. Therefore, we shouldn't be
checking the requested tiling type, but rather the granted tiling
2. The existing code can fall back to X-tiled even if choose_tiling said
X-tiling was not okay.

Neither of these are probably actually an issue, but this simply makes the code
correct.

The changes behavior originally introduced here:
commit cbe24ff7c8d69a6d378d9c2cce2bc117517f4302
Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Wed Apr 10 13:49:16 2013 -0700

    intel: Fall back to X-tiling when larger than estimated aperture size.

v2: This was rebased on a recent commit than Anuj pushed since I originally
authored the patch.
commit 524a729f68c15da3fc6c42b3158a13e0b84c2728
Author: Anuj Phogat <anuj.phogat at gmail.com>
Date:   Tue Feb 17 10:40:58 2015 -0800

    i965: Fix condition to use Y tiling in blitter in intel_miptree_create()

v3: Removed the check against X-tiling since its removal in
9f78e27fc60b3473b708ab4ca04e4ebd6be6cf4e

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 src/mesa/drivers/dri/i965/intel_mipmap_tree.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
index e85c3f0..e0a7f11 100644
--- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
+++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
@@ -651,10 +651,7 @@ intel_miptree_create(struct brw_context *brw,
       total_height = ALIGN(total_height, 64);
    }
 
-   bool y_or_x = false;
-
    if (mt->tiling == (I915_TILING_Y | I915_TILING_X)) {
-      y_or_x = true;
       mt->tiling = I915_TILING_Y;
    }
 
@@ -684,7 +681,9 @@ intel_miptree_create(struct brw_context *brw,
     * BLT engine to support it.  Prior to Sandybridge, the BLT paths can't
     * handle Y-tiling, so we need to fall back to X.
     */
-   if (brw->gen < 6 && y_or_x && mt->bo->size >= brw->max_gtt_map_object_size) {
+   if (brw->gen < 6 &&
+       mt->bo->size >= brw->max_gtt_map_object_size &&
+       mt->tiling == I915_TILING_Y) {
       perf_debug("%dx%d miptree larger than aperture; falling back to X-tiled\n",
                  mt->total_width, mt->total_height);
 
-- 
2.5.0