radv: Do not set SX DISABLE bits for RB+ with unused surfaces.

The extra bits in CB_SHADER_MASK break dual source blending in
SkQP on a Stoney device. However:

- As far as I can tell, some other dual source blend tests are passing
  before and after the change.
- A hacked around skqp passes on my Vega desktop and Raven laptop
- Getting Skqp to give any useful info or to run it outside of Android
  on ChromeOS is proving difficult.

I have confirmed 3 strategies that seem to work:
- The old radv behavior of setting CB_SHADER_MASK to 0xF
- AMDVLK: CB_SHADER_MASK = 0xFF, and the 3 RB+ regs
  are 0.
- radeonsi: CB_SHADER_MASK = 0xFF, but does not set DISABLE
  bits in SX_BLEND_OPT_CONTROL for CB 1-7.

Let us use the radeonsi solution as that solution also seems like the correct
thing to do for holes. I have tested on my Raven laptop that setting the high
surfaces to not disabled and downconvert to 32_R does not imply a performance
penalty.

Fixes: e9316fdfd48 "radv: fix setting CB_SHADER_MASK for dual source blending"
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3670>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3670>
(cherry picked from commit 65a6dc5139fddd5e01eaedcc57fc67e0a6a28c94)

2 files changed, 8 insertions, 7 deletions

diff --git a/.pick_status.json b/.pick_status.json
index 78418eea96f..f9a84aff49b 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -283,7 +283,7 @@
         "description": "radv: Do not set SX DISABLE bits for RB+ with unused surfaces.",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": "e9316fdfd4899c269a19e106a6ffa4309ae48b27"
     },
diff --git a/src/amd/vulkan/radv_cmd_buffer.c b/src/amd/vulkan/radv_cmd_buffer.c
index 21ef5caa8e5..549b7e8843d 100644
--- a/src/amd/vulkan/radv_cmd_buffer.c
+++ b/src/amd/vulkan/radv_cmd_buffer.c
@@ -996,8 +996,9 @@ radv_emit_rbplus_state(struct radv_cmd_buffer *cmd_buffer)
 
 	for (unsigned i = 0; i < subpass->color_count; ++i) {
 		if (subpass->color_attachments[i].attachment == VK_ATTACHMENT_UNUSED) {
-			sx_blend_opt_control |= S_02875C_MRT0_COLOR_OPT_DISABLE(1) << (i * 4);
-			sx_blend_opt_control |= S_02875C_MRT0_ALPHA_OPT_DISABLE(1) << (i * 4);
+			/* We don't set the DISABLE bits, because the HW can't have holes,
+			 * so the SPI color format is set to 32-bit 1-component. */
+			sx_ps_downconvert |= V_028754_SX_RT_EXPORT_32_R << (i * 4);
 			continue;
 		}
 
@@ -1113,10 +1114,10 @@ radv_emit_rbplus_state(struct radv_cmd_buffer *cmd_buffer)
 		}
 	}
 
-	for (unsigned i = subpass->color_count; i < 8; ++i) {
-		sx_blend_opt_control |= S_02875C_MRT0_COLOR_OPT_DISABLE(1) << (i * 4);
-		sx_blend_opt_control |= S_02875C_MRT0_ALPHA_OPT_DISABLE(1) << (i * 4);
-	}
+	/* Do not set the DISABLE bits for the unused attachments, as that
+	 * breaks dual source blending in SkQP and does not seem to improve
+	 * performance. */
+
 	/* TODO: avoid redundantly setting context registers */
 	radeon_set_context_reg_seq(cmd_buffer->cs, R_028754_SX_PS_DOWNCONVERT, 3);
 	radeon_emit(cmd_buffer->cs, sx_ps_downconvert);