Mesa (master): pan/bi: Document register conventions

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Module: Mesa
Branch: master
Commit: 8fde30925d9c13df9003ab34bd8fafe404ff2284
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=8fde30925d9c13df9003ab34bd8fafe404ff2284

Author: Alyssa Rosenzweig <alyssa at collabora.com>
Date:   Mon Mar  1 19:55:07 2021 +0000

pan/bi: Document register conventions

Should motiviate RA decisions.

Signed-off-by: Alyssa Rosenzweig <alyssa at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9421>

---

 src/panfrost/bifrost/README.md | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/panfrost/bifrost/README.md b/src/panfrost/bifrost/README.md
new file mode 100644
index 00000000000..2838d41846f
--- /dev/null
+++ b/src/panfrost/bifrost/README.md
@@ -0,0 +1,25 @@
+# Bifrost compiler
+
+## Register file
+
+Defined partially in software, partially in hardware.
+
+## Blend shaders
+
+R0 - R3: input (color #0)
+R4 - R7: input (color #1)
+R8 - R15: general purpose
+R48: return address
+
+## Fragment
+
+Anything live during BLEND must respect blend shader registers.
+
+R0 - R3: preloaded (message #0)
+R4 - R7: preloaded (message #1)
+R57 - R63: preloaded (various)
+
+R0 - R15: general purpose (full threads)
+R48 - R63: general purpose (full threads)
+
+R32 - R47: general purpose (half threads, or v6)