Daniel Vetter daniel.vetter@ffwll.ch writes:
Everyone knows them, except all the new folks joining from the ARM side haven't lived through all the pain of the past years and are entirely surprised when I raise this. Definitely time to document this.
Documentation/gpu/drm-uapi.rst | 67 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+)
diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 94876938aef3..a7e3aa27167d 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -36,6 +36,73 @@ Primary Nodes, DRM Master and Authentication Open-Source Userspace Requirements ==================================
+The DRM subsystem has stricter requirements on what the userspace side for new +uAPI needs to look like. This section here explains what exactly those +requirements are, and why they exist.
+The short summary is that any addition of DRM uAPI requires corresponding +open-sourced userspace patches, and those patches must be reviewed and ready for +merging into a suitable and canonical upstream project.
+GFX devices (both display and render/GPU side) are really complex bits of hardware, +with userspace and kernel by necessity having to work together really closely. +The interfaces, for rendering and modesetting must be extremely wide and
I think there should be another comma after "modesetting".
+flexible, and therefore it is almost always impossible to precisely define them +for every possible corner case. This in turns makes it really practically
"in turn"
+These are fairly steep requirements, but have grown out from years of shared +pain and experience with uAPI added hastily, and almost always regretted about +as fast. GFX devices change really fast, requiring a paradigm shift and entire +new set of uAPI interfaces every few years at least. Together with the Linux +kernel's guarantee to keep existing userspace running for 10+ years this is +already rather painful for the DRM subsystem, with multiple different uAPIs for +the same thing co-existing. If we'd add a few more complete mistakes into the
"If we"
+mix every year it would be entirely unmanagable.
With the little nitpicks (probably) fixed,
Reviewed-by: Eric Anholt eric@anholt.net