[Mesa-dev] [PATCH] i965: Disable fast clears for MSRTs on SKL

[Neil Roberts]

There are currently a bunch of formats that behave strangely when
sampling the cleared color from the MCS buffer on SKL. They seem to
mostly be formats that don't have an alpha component, although it's
not all of them, and we haven't yet found anything in the specs which
would explain this. For now to be on the safe side this patch just
disables fast clears for MSRTs on SKL altogether. The assumption is
that clears are probably more likely to be used in single-sampled
applications anyway so we can at least get them working and we can
enable MSRTs later once we understand the problem better.
---

If we go with this patch we could remove the explicit check for the
half-float intensity and luminance formats as well.

 src/mesa/drivers/dri/i965/brw_meta_fast_clear.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c b/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
index dc085ba..85576a8 100644
--- a/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
+++ b/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
@@ -524,6 +524,13 @@ brw_meta_fast_clear(struct brw_context *brw, struct gl_framebuffer *fb,
       if (brw->gen < 7)
          clear_type = REP_CLEAR;
 
+      /* Certain formats have unresolved issues with sampling from the MCS
+       * buffer on Gen9. This disables fast clears altogether for MSRTs until
+       * we can figure out what's going on.
+       */
+      if (brw->gen >= 9 && irb->mt->num_samples > 1)
+         clear_type = REP_CLEAR;
+
       if (irb->mt->fast_clear_state == INTEL_FAST_CLEAR_STATE_NO_MCS)
          clear_type = REP_CLEAR;
 
-- 
1.9.3