[Mesa-dev] [PATCH 3/4] i965: Defeat the register stride checker in URB reads.

[Kenneth Graunke]

Pulling DF inputs from the URB generates messages like:

   send(8)         g23<1>DF        g1<8,8,1>UD
                   urb 3 SIMD8 read mlen 1 rlen 2      { align1 1Q };

which makes the simulator angry:

   "For 64-bit Align1 operation or multiplication of dwords in CHV,
    source horizontal stride must be aligned to qword."

This seems to be documented in the Cherryview PRM, Volume 7, Page 823:

   "When source or destination datatype is 64b or operation is integer
    DWord multiply, regioning in Align1 must follow these rules:

    1. Source and Destination horizontal stride must be aligned to the
       same qword."

Setting the source horizontal stride to QWord is insane, as it's the
message header containing 8 URB handles in a single 32-bit DWord.
Instead, we should whack the destination type to UD, D, or F so that
the register stride checker doesn't notice.  The destination type of
send messages is basically irrelevant anyway.

Cc: "12.0" <mesa-stable at lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95462
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
index 93a9519..8faa856 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
@@ -440,7 +440,7 @@ fs_generator::generate_urb_read(fs_inst *inst,
    assert(header.type == BRW_REGISTER_TYPE_UD);
 
    brw_inst *send = brw_next_insn(p, BRW_OPCODE_SEND);
-   brw_set_dest(p, send, dst);
+   brw_set_dest(p, send, retype(dst, BRW_REGISTER_TYPE_UD));
    brw_set_src0(p, send, header);
    brw_set_src1(p, send, brw_imm_ud(0u));
 
-- 
2.8.3