[PATCH] unstable/linux-dmabuf: Add 'direct_display' flag

[Marius Vlad]

Flag used to tell the compositor that it should avoid touching the
dmabuf buffer and forward it directly to the display controller.

Most likely this flag can be used together with the content-protection
protocol. It assures the client that the compositor will never handle
the buffer over to the GPU but instead it will forward it straight to
the display controller.

While content-protection protocol should be sufficient to restrict the
content on certain displays, on certain hardware platforms the GPU is
not a secure-path link in the secure-content-path chain, and as such,
this flag would be necessary to avoid passing the dmabuf buffer
over to the GPU altogether. GPUs reading the dmabuf residing in a
specially designed memory zone would be seen as an illegal memory access.

Other example include video players which might need this flag passed
down to avoid doing any composition, thus having an improvement of
bandwidth usage and performance. Set-up boxes with dedicated video
players could use this facility alongside the Pixman renderer, is
another potential example of why this flag would be useful.

Bumps zwp_linux_dmabuf_v1 and zwp_linux_buffer_params_v1 to version 4.

Signed-off-by: Marius Vlad <marius.vlad at collabora.com>

---
This patch initially started as fork at
https://gitlab.freedesktop.org/marius.vlad0/wayland-protocols/merge_requests/3

This flag was used to be called 'no_gpu_import' but 'direct_display'
should better reflect its name and purpose.

Lastly, a WIP for the implementation of this flag for weston is at
https://gitlab.freedesktop.org/wayland/weston/merge_requests/298, which
should follow up closely.
---
 .../linux-dmabuf/linux-dmabuf-unstable-v1.xml     | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml b/unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml
index b43e81c..5b4b1e6 100644
--- a/unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml
+++ b/unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml
@@ -2,7 +2,7 @@
 <protocol name="linux_dmabuf_unstable_v1">
 
   <copyright>
-    Copyright © 2014, 2015 Collabora, Ltd.
+    Copyright © 2014, 2015, 2019 Collabora, Ltd.
 
     Permission is hereby granted, free of charge, to any person obtaining a
     copy of this software and associated documentation files (the "Software"),
@@ -24,7 +24,7 @@
     DEALINGS IN THE SOFTWARE.
   </copyright>
 
-  <interface name="zwp_linux_dmabuf_v1" version="3">
+  <interface name="zwp_linux_dmabuf_v1" version="4">
     <description summary="factory for creating dmabuf-based wl_buffers">
       Following the interfaces from:
       https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_image_dma_buf_import.txt
@@ -149,7 +149,7 @@
     </event>
   </interface>
 
-  <interface name="zwp_linux_buffer_params_v1" version="3">
+  <interface name="zwp_linux_buffer_params_v1" version="4">
     <description summary="parameters for creating a dmabuf-based wl_buffer">
       This temporary object is a collection of dmabufs and other
       parameters that together form a single logical buffer. The temporary
@@ -229,6 +229,7 @@
       <entry name="y_invert" value="1" summary="contents are y-inverted"/>
       <entry name="interlaced" value="2" summary="content is interlaced"/>
       <entry name="bottom_first" value="4" summary="bottom field first"/>
+      <entry name="direct_display" value="8" summary="forward buffer to display controller" since="4"/>
     </enum>
 
     <request name="create">
@@ -254,6 +255,14 @@
         'bottom_first' is specified. It is undefined whether 'bottom_first'
         is ignored if 'interlaced' is not set.
 
+        Flag 'direct_display' tells the compositor not to import it to the GPU
+        in order to bypass it entirely, such that the buffer will be directly
+        scanned-out by the display controller. If HW is not capable/or there
+        aren't any available resources to directly scan-out the buffer, a
+        placeholder should be installed in-place by the compositor. The
+        compositor may perform checks on the dmabuf and refuse to create a
+        wl_buffer if the dmabuf seems unusable for being used directly.
+
         This protocol does not convey any information about field rate,
         duration, or timing, other than the relative ordering between the
         two fields in one buffer. A compositor may have to estimate the
-- 
2.24.0