[RFC] Host1x/TegraDRM UAPI

[Daniel Vetter]

On Fri, Jun 26, 2020 at 04:59:45PM +0300, Dmitry Osipenko wrote:
> 26.06.2020 16:38, Daniel Vetter пишет:
> > On Fri, Jun 26, 2020 at 01:40:40PM +0200, Thierry Reding wrote:
> >> On Fri, Jun 26, 2020 at 01:06:58PM +0200, Karol Herbst wrote:
> >>> On Tue, Jun 23, 2020 at 3:03 PM Mikko Perttunen <cyndis at kapsi.fi> wrote:
> >>>>
> >>>> # Host1x/TegraDRM UAPI proposal
> >>>>
> >>>> This is a proposal for a stable UAPI for Host1x and TegraDRM, to replace
> >>>> the current TegraDRM UAPI that is behind `STAGING` and quite obsolete in
> >>>> many ways.
> >>>>
> >>>> I haven't written any implementation yet -- I'll do that once there is
> >>>> some agreement on the high-level design.
> >>>>
> >>>> Current open items:
> >>>>
> >>>> * The syncpoint UAPI allows userspace to create sync_file FDs with
> >>>> arbitrary syncpoint fences. dma_fence code currently seems to assume all
> >>>> fences will be signaled, which would not necessarily be the case with
> >>>> this interface.
> >>>> * Previously present GEM IOCTLs (GEM_CREATE, GEM_MMAP) are not present.
> >>>> Not sure if they are still needed.
> >>>>
> >>>
> >>> Hi, as this wasn't addressed here (and sorry if I missed it): is there
> >>> an open source userspace making use of this UAPI? Because this is
> >>> something which needs to be seen before it can be included at all.
> >>
> >> There's a set of commits that implement an earlier draft here:
> >>
> >>     https://github.com/thierryreding/linux/tree/for-5.6/drm-tegra-destage-abi
> >>
> >> and corresponding changes to libdrm to make use of that and implement
> >> tests using the various generations of VIC here:
> >>
> >>     https://cgit.freedesktop.org/~tagr/drm/log/
> >>
> >> Before actually jumping to an implementation we wanted to go over the
> >> design a bit more to avoid wasting a lot of work, like we've done in
> >> the past. Turns out it isn't easy to get everyone to agree on a good
> >> ABI. Who would've thought? =)
> >>
> >> I expect that once the discussion around the ABI settles Mikko will
> >> start on implementing this ABI in the kernel and we'll update the
> >> libdrm patches to make use of the new ABI as well.
> > 
> > Do we have more than libdrm and tests for this, like something somewhat
> > functional? Since tegradrm landed years ago we've refined the criteria a
> > bit in this regard, latest version is explicit in that it needs to be
> > something that's functional (for end-users in some form), not just
> > infrastructure and tests.
> 
> We have Opentegra [1] and VDPAU [2] userspace drivers for older Tegra
> SoCs that have been using the staging UAPI for years now.
> 
> [1] https://github.com/grate-driver/xf86-video-opentegra
> [2] https://github.com/grate-driver/libvdpau-tegra
> 
> The UAPI and the kernel driver updates are very needed for these drivers
> because of the missing UAPI synchronization features and performance
> problems of the kernel driver.
> 
> So we already have some real-world userspace for the testing!

Awesome! Maybe for future rounds include the links for the vdpau driver. I
didn't know about that one at all. -opentegra is probably not so relevant
anymore (and I flat out forgot it exists) ... Including the userspace side
links is good so that forgetful people like me don't nag :-)
-Daniel


> It's not the first and not the second time we're discussing the Tegra
> DRM UAPI changes, but this time it feels like there is a good chance
> that it will finally materialize and I'm very happy about it :)

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch