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.widaw...@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 CHV.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84212
Cc: Matt Turner <matts...@gmail.com>
Signed-off-by: Ben Widawsky <b...@bwidawsk.net>
---
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 2fb578e..082bb1e 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -719,11 +719,11 @@ 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]))
--
2.2.1
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