Daniel Vetter <daniel.vetter@xxxxxxxx> 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@xxxxxxxxxx>
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