Mesa (main): broadcom/compiler: improve documentation for Z writes

[GitLab Mirror]

Module: Mesa
Branch: main
Commit: cc7db1fc537ea81310160be78716736544a51a9c
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=cc7db1fc537ea81310160be78716736544a51a9c

Author: Iago Toral Quiroga <itoral at igalia.com>
Date:   Fri Dec  3 10:44:14 2021 +0100

broadcom/compiler: improve documentation for Z writes

Reviewed-by: Alejandro Piñeiro <apinheiro at igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14037>

---

 src/broadcom/compiler/nir_to_vir.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/broadcom/compiler/nir_to_vir.c b/src/broadcom/compiler/nir_to_vir.c
index 6e645204b79..e93e754c51a 100644
--- a/src/broadcom/compiler/nir_to_vir.c
+++ b/src/broadcom/compiler/nir_to_vir.c
@@ -1707,10 +1707,12 @@ emit_frag_end(struct v3d_compile *c)
                 c->s->info.fs.early_fragment_tests = true;
         }
 
-        /* By default, the FEP will perform early fragment tests. This can be
-         * disabled when needed (Z writes from shader, discards, etc), by
-         * setting c->writes_z to True, in which case, the QPUs need to write
-         * the Z value.
+        /* By default, Z buffer writes are implicit using the Z values produced
+         * from FEP (Z value produced from rasterization). When this is not
+         * desirable (shader writes Z explicitly, has discards, etc) we need
+         * to let the hardware know by setting c->writes_z to true, in which
+         * case we always need to write a Z value from the QPU, even if it is
+         * just the passthrough Z value produced from FEP.
          *
          * Also, from the V3D 4.2 spec:
          *