freedreno/ir3: Drop the max_const on a6xx to 512.

The GLES blob on the p3a limits constlen to 512 between VS and FS across
a6xx gpu ids (615, 630, 640, and 650).  Experimentally, exceeding that
limit in any one stage results in rendering corruption or GPU hangs
(though my most detailed testing had a loop limit in a uniform, so that
may the cause of the hang).  Clamp the limit we use inside of a shader so
we don't exceed it within a stage.

This commit doesn't resovle limiting inter-stage.  Experimentally, I've
found that I can push up to a total of ~768 vec4s between VS and FS on
a630, with or without uniform updates between each draw.  We'll need to do
some shader key-based limiting of constlen at draw time to respect that
limit, but that's left for future work, and this commit is enough for the
google earth case that initiated this work.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5273>

diff --git a/src/freedreno/ir3/ir3_compiler.c b/src/freedreno/ir3/ir3_compiler.c
index 366e2008f8b6f9aa8ab5ac085a5927e56e0cd212..76404fd7a52af583be66d261b475297c17e05c1a 100644 (file)
--- a/src/freedreno/ir3/ir3_compiler.c
+++ b/src/freedreno/ir3/ir3_compiler.c
@@ -73,7 +73,10 @@ struct ir3_compiler * ir3_compiler_create(struct fd_device *dev, uint32_t gpu_id
                compiler->unminify_coords = false;
                compiler->txf_ms_with_isaml = false;
                compiler->array_index_add_half = true;
-               compiler->max_const = 1024;
+               /* Some a6xxs can apparently do 640 consts, but not all.  Need to
+                * characterize this better across GPUs
+                */
+               compiler->max_const = 512;
                compiler->const_upload_unit = 4;
        } else {
                /* no special handling for "flat" */