Mesa (master): intel/fs: Work around dual-source blending hangs in combination with SIMD16

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Module: Mesa
Branch: master
Commit: 296c04d78c9840f83e7fcaf9b45a4cee96752348
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=296c04d78c9840f83e7fcaf9b45a4cee96752348

Author: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
Date:   Thu May 14 15:29:36 2020 +0300

intel/fs: Work around dual-source blending hangs in combination with SIMD16

It was found that dual-source blending hangs with SIMD16 dispatch in some
specific but unknown situation. Which in the wild happen when rgba
anti-aliasing is enabled for fonts.

Cc: <mesa-stable at lists.freedesktop.org>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2183
Signed-off-by: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5037>

---

 src/intel/compiler/brw_fs_visitor.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/intel/compiler/brw_fs_visitor.cpp b/src/intel/compiler/brw_fs_visitor.cpp
index 7b315693e4a..22e83f1adb9 100644
--- a/src/intel/compiler/brw_fs_visitor.cpp
+++ b/src/intel/compiler/brw_fs_visitor.cpp
@@ -548,9 +548,13 @@ fs_visitor::emit_fb_writes()
        * XXX - Emit an extra single-source NULL RT-write marked LastRT in
        *       order to release the thread dependency without disabling
        *       SIMD32.
+       *
+       * The dual-source RT write messages may lead to hangs with SIMD16
+       * dispatch on ICL due some unknown reasons, see
+       * https://gitlab.freedesktop.org/mesa/mesa/-/issues/2183
        */
-      limit_dispatch_width(16, "Dual source blending unsupported "
-                           "in SIMD32 mode.\n");
+      limit_dispatch_width(8, "Dual source blending unsupported "
+                           "in SIMD16 and SIMD32 modes.\n");
    }
 }