Am 19.08.2016 um 23:43 schrieb Eric Anholt: > Daniel Vetter <daniel.vetter at 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.
Oh, yes please. >> --- >> 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 at anholt.net> I read through it and can't find anything more to add. So with Eric's comments fixed the patch is Reviewed-by: Christian König <christian.koenig at amd.com>. Additional to that I think with our hybrid stack this is rather important for AMD. So I'm going to forward it to a few people internally as well. Regards, Christian.
