[Mesa-dev] [PATCH 10/12] panfrost: Document "depth buffer writeback" bit

[Alyssa Rosenzweig]

We were setting this bit as a magic value for a while when using depth
FBOs, but it is only now clear what the meaning is.

Signed-off-by: Alyssa Rosenzweig <alyssa at rosenzweig.io>
---
 src/gallium/drivers/panfrost/include/panfrost-job.h | 8 ++++++++
 src/gallium/drivers/panfrost/pan_context.c          | 5 ++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/gallium/drivers/panfrost/include/panfrost-job.h b/src/gallium/drivers/panfrost/include/panfrost-job.h
index d719325d07b..3c5ed2bc802 100644
--- a/src/gallium/drivers/panfrost/include/panfrost-job.h
+++ b/src/gallium/drivers/panfrost/include/panfrost-job.h
@@ -1457,6 +1457,14 @@ struct bifrost_fb_extra {
 } __attribute__((packed));
 
 /* flags for unk3 */
+
+/* Enables writing depth results back to main memory (rather than keeping them
+ * on-chip in the tile buffer and then discarding) */
+
+#define MALI_MFBD_DEPTH_WRITE (1 << 10)
+
+/* The MFBD contains the extra bifrost_fb_extra section*/
+
 #define MALI_MFBD_EXTRA (1 << 13)
 
 struct bifrost_framebuffer {
diff --git a/src/gallium/drivers/panfrost/pan_context.c b/src/gallium/drivers/panfrost/pan_context.c
index 37f6ce4910f..419c1a4eb6f 100644
--- a/src/gallium/drivers/panfrost/pan_context.c
+++ b/src/gallium/drivers/panfrost/pan_context.c
@@ -270,7 +270,7 @@ panfrost_set_fragment_target_zsbuf(
 
                 ctx->fragment_extra.unk = 0x400 | 0x20 | 0x10 | 0x5;
 
-                ctx->fragment_mfbd.unk3 |= 0x400;
+                ctx->fragment_mfbd.unk3 |= MALI_MFBD_DEPTH_WRITE;
         } else if (rsrc->bo->layout == PAN_LINEAR) {
                 /* TODO: explicit depth on SFBD */
                 assert(!require_sfbd);
@@ -282,8 +282,7 @@ panfrost_set_fragment_target_zsbuf(
                 ctx->fragment_extra.ds_linear.depth = rsrc->bo->gpu[0];
                 ctx->fragment_extra.ds_linear.depth_stride = stride;
 
-                /* Seemingly means "write to depth buffer" */
-                ctx->fragment_mfbd.unk3 |= 0x400;
+                ctx->fragment_mfbd.unk3 |= MALI_MFBD_DEPTH_WRITE;
         } else {
                 fprintf(stderr, "Invalid render layout (zsbuf)");
                 assert(0);
-- 
2.20.1