[Mesa-dev] [PATCH] i965/skl: Don't use the PMA depth stall workaround

[Ben Widawsky]

The PMA depth stall must be enabled (optimization turned off) under certain
circumstances on gen8. This was supposedly fixed for Gen9, which means we do not
need to check, or toggle the state. The hardware is supposed to enable the
hardware optimization by default, unlike BDW, so we also don't need to set it at
init. For whatever reason this improves stability on ETQW with the bug mentioned
below.

TODO: This patch still needs to be tested on a full piglit run.

References: https://bugs.freedesktop.org/show_bug.cgi?id=89039 (doesn't fix)
Cc: Anuj Phogat <anuj.phogat at intel.com>
Cc: Eero Tamminen <eero.t.tamminen at intel.com>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 src/mesa/drivers/dri/i965/gen8_depth_state.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/gen8_depth_state.c b/src/mesa/drivers/dri/i965/gen8_depth_state.c
index c6494c9..3d126cf 100644
--- a/src/mesa/drivers/dri/i965/gen8_depth_state.c
+++ b/src/mesa/drivers/dri/i965/gen8_depth_state.c
@@ -368,6 +368,10 @@ static void
 gen8_emit_pma_stall_workaround(struct brw_context *brw)
 {
    uint32_t bits = 0;
+
+   if (brw->gen >= 9)
+      return;
+
    if (pma_fix_enable(brw))
       bits |= GEN8_HIZ_NP_PMA_FIX_ENABLE | GEN8_HIZ_NP_EARLY_Z_FAILS_DISABLE;
 
@@ -400,7 +404,8 @@ gen8_hiz_exec(struct brw_context *brw, struct intel_mipmap_tree *mt,
       return;
 
    /* Disable the PMA stall fix since we're about to do a HiZ operation. */
-   write_pma_stall_bits(brw, 0);
+   if (brw->gen == 8)
+      write_pma_stall_bits(brw, 0);
 
    assert(mt->first_level == 0);
    assert(mt->logical_depth0 >= 1);
-- 
2.3.3