Mesa (staging/20.1): panfrost: Fix background showing when using discard

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Module: Mesa
Branch: staging/20.1
Commit: b62f3a931af7b2736deaa9323cc53fdf6246a432
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=b62f3a931af7b2736deaa9323cc53fdf6246a432

Author: Icecream95 <ixn at keemail.me>
Date:   Tue May 12 14:08:09 2020 +1200

panfrost: Fix background showing when using discard

This fixes problems in a number of games, including SuperTuxKart,
OpenMW and RVGL.

v2: Use MALI_READS_ZS | 0x20 instead of MALI_WRITES_Z to match with
the blob. Keep using 0x400 | 0x20 when depth is disabled.

Closes: #2620
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
(cherry picked from commit 0dd24b381c52e0b20fe70041e95611aad6b0d258)

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5193>

---

 src/gallium/drivers/panfrost/pan_cmdstream.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/gallium/drivers/panfrost/pan_cmdstream.c b/src/gallium/drivers/panfrost/pan_cmdstream.c
index 6c667d2017d..42d77ca09f0 100644
--- a/src/gallium/drivers/panfrost/pan_cmdstream.c
+++ b/src/gallium/drivers/panfrost/pan_cmdstream.c
@@ -742,8 +742,14 @@ panfrost_frag_shader_meta_init(struct panfrost_context *ctx,
          * related to forward-pixel kill, as per "Mali Performance 3: Is
          * EGL_BUFFER_PRESERVED a good thing?" by Peter Harris */
 
+        const struct pipe_depth_stencil_alpha_state *zsa = ctx->depth_stencil;
+
+        bool depth_enabled = fs->writes_depth ||
+           (zsa && zsa->depth.enabled && zsa->depth.func != PIPE_FUNC_ALWAYS);
+
         SET_BIT(fragmeta->unknown2_3, MALI_CAN_DISCARD, fs->can_discard);
-        SET_BIT(fragmeta->midgard1.flags_lo, 0x400, fs->can_discard);
+        SET_BIT(fragmeta->midgard1.flags_lo, 0x400, !depth_enabled && fs->can_discard);
+        SET_BIT(fragmeta->midgard1.flags_lo, MALI_READS_ZS, depth_enabled && fs->can_discard);
 
         panfrost_frag_meta_rasterizer_update(ctx, fragmeta);
         panfrost_frag_meta_zsa_update(ctx, fragmeta);