[Mesa-dev] [RFC] gpu/docs: Clarify what userspace means for gl

[Daniel Vetter]

Clear rules avoid arguing.

I think it'd be good to have an equally solid list on the kms side.
But kms is much more meant to be a standard, and the list of userspace
projects we've accepted in the past is constantly shifting and
adjusting. So I figured I'll leave that as an exercise for later on.

v2: Try to clarify that we don't want a mesa driver just for mesa's
sake, and more clearly exclude anything that just doesn't make sense
technically.  Example would be a compute driver that makes sense to be
merged into drm (for kernel side code-sharing), but where the intended
use is some single-source CUDA-style compute without ever bothering
about any of the 3D/rendering side baggage that comes with gl/vk.

v3: Drop vulkan for now, the situation there isn't as obviously
clear-cut as on the gl side, and I don't want to tank this idea on a
hot discussion about vk and mesa. Plus I think once we have 1-2 more
vk drivers in mesa the situation on the vk side is clear-cut too, and
we can do a follow-up patch to add vk to the list where we expect the
userspace to be in upstream mesa. That's would give nice precedence to
make it clear that this isn't cast in stone, but meant to reflect
reality and should be adjusted as needed.

v4: Fix typo.

Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
Hi all,

I discussed this a bit with a few people over the past few months (I
think), to get a feel for where the consensus might be. Goal here isn't
anything aspirational (like with the recent igt patch), but just
documented current expectations, so that there's no confusion or companies
with failed projects that had no reason to fail. Same reasons really like
for the patch to document open source userspace requirements a few years
ago, that one is still extremely useful.

For obvious reasons needs solid support from both mesa and kernel people,
or it won't land.

Thoughts, hot takes, comments, also acks all very much welcome.

Thanks, Daniel
---
 Documentation/gpu/drm-uapi.rst | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index c9fd23efd957..79f78c3fa458 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -105,6 +105,29 @@ is already rather painful for the DRM subsystem, with multiple different uAPIs
 for the same thing co-existing. If we add a few more complete mistakes into the
 mix every year it would be entirely unmanageable.
 
+Below some clarifications what this means for specific areas in DRM.
+
+Compute&Rendering Userspace
+---------------------------
+
+Userspace API for enabling compute and rendering blocks which are capable of at
+least supporting one of the OpenGL or OpenGL ES standards from Khronos need to
+be enabled in the upstream `Mesa3D project<https://www.mesa3d.org/>`.
+
+Mesa3D is the canonical upstream for these areas because it is a fully
+compliant, performant and cross-vendor implementation that supports all kernel
+drivers in DRM. It is therefore the best platform to validate userspace API and
+especially make sure that cross-vendor interoperation is assured.
+
+Other userspace is only admissible if exposing a given feature through OpenGL or
+OpenGL ES would result in a technically unsound design, incomplete driver or
+otherwise an implementation which isn't useful in real world usage.
+
+Other areas, like media codec, which Mesa3D supports for just some drivers, but
+isn't the clear universal choice, are excluded from this policy. Driver teams
+are still encourage to aim for shared, cross-vendor infrastructure in userspace
+as much as possible.
+
 .. _drm_render_node:
 
 Render nodes
-- 
2.20.1