Mesa (master): i965/vec4: Correct MUL destination hazard

[Ben Widawsky]

Module: Mesa
Branch: master
Commit: 8030e269e911c4f90a44d9a77eb342dd2657d229
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=8030e269e911c4f90a44d9a77eb342dd2657d229

Author: Ben Widawsky <benjamin.widawsky at intel.com>
Date:   Tue Dec  2 17:30:49 2014 -0800

i965/vec4: Correct MUL destination hazard

As it turns out, we were over-thinking the cause of the hang on
Cherryview. It's simply errata for Cherryview.

commit 88fea85f09e2252035bec66ab26c375b45b000f5
Author: Ben Widawsky <benjamin.widawsky at intel.com>
Date:   Fri Nov 21 10:47:41 2014 -0800

    i965/vec4/gen8: Handle the MUL dest hazard exception

This is an explanation to why we never saw the hang on BDW.

NOTE: The problem the original patch was trying to fix does still exist. It will
have to be fixed at some point.

v2: Modify commit message, s/CHV/BDW

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84212
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
Reviewed-by: Matt Turner <mattst88 at gmail.com>

---

 src/mesa/drivers/dri/i965/brw_vec4.cpp |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index 8988196..98fad6c 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -822,11 +822,11 @@ vec4_visitor::is_dep_ctrl_unsafe(const vec4_instruction *inst)
    (reg.type == BRW_REGISTER_TYPE_UD || \
     reg.type == BRW_REGISTER_TYPE_D)
 
-   /* From the destination hazard section of the spec:
-    * > Instructions other than send, may use this control as long as operations
-    * > that have different pipeline latencies are not mixed.
+   /* "When source or destination datatype is 64b or operation is integer DWord
+    * multiply, DepCtrl must not be used."
+    * May apply to future SoCs as well.
     */
-   if (brw->gen >= 8) {
+   if (brw->is_cherryview) {
       if (inst->opcode == BRW_OPCODE_MUL &&
          IS_DWORD(inst->src[0]) &&
          IS_DWORD(inst->src[1]))