On Tue, 4 Sep 2018 at 03:00, Thomas Hellstrom <thellstrom at vmware.com> wrote: > > On 09/03/2018 06:33 PM, Daniel Vetter wrote: > > On Mon, Sep 03, 2018 at 11:16:29AM +0200, Thomas Hellstrom wrote: > >> On 08/31/2018 05:30 PM, Thomas Hellstrom wrote: > >>> On 08/31/2018 05:27 PM, Emil Velikov wrote: > >>>> On 31 August 2018 at 15:38, Michel Dänzer <michel at daenzer.net> wrote: > >>>>> [ Adding the amd-gfx list ] > >>>>> > >>>>> On 2018-08-31 3:05 p.m., Thomas Hellstrom wrote: > >>>>>> On 08/31/2018 02:30 PM, Emil Velikov wrote: > >>>>>>> On 31 August 2018 at 12:54, Thomas Hellstrom <thellstrom at vmware.com> > >>>>>>> wrote: > >>>>>>>> To determine whether a device node is a drm device > >>>>>>>> node or not, the code > >>>>>>>> currently compares the node's major number to the static drm major > >>>>>>>> device > >>>>>>>> number. > >>>>>>>> > >>>>>>>> This breaks the standalone vmwgfx driver on XWayland dri clients, > >>>>>>>> > >>>>>>> Any particular reason why the code doesn't use a fixed node there? > >>>>>>> It will make the diff vs the in-kernel driver a bit smaller. > >>>>>> Because then it won't be able to interoperate with other in-tree > >>>>>> drivers, like virtual drm drivers or passthrough usb drm drivers. > >>>>>> There is no clean way to share the minor number allocation > >>>>>> with in-tree > >>>>>> drm, so standalone vmwgfx is using dynamic major allocation. > >>>>> I wonder why I haven't heard of any of these issues with the standalone > >>>>> version of amdgpu shipped in packaged AMD releases. Does that > >>>>> also use a > >>>>> different major number? If yes, maybe it's just that nobody has tried > >>>>> Xwayland clients with that driver. If no, how does it avoid the other > >>>>> issues described above? > >>>>> > >>>> AFAICT, the difference is that the standalone vmwgfx uses an internal > >>>> copy of drm core. > >>>> It doesn't reuse the in-kernel drm, hence it cannot know which minor > >>>> it can use. > >>>> > >>>> -Emil > >>> Actually, standalone vmwgfx could perhaps also try to allocate minors > >>> from 63 and downwards. That might work, but needs some verification. > >>> > >> So unfortuntately this doesn't work since the in-tree drm's file operations > >> are registered with the DRM_MAJOR. > >> So I still think the patch is the way to go. If people are concerned that > >> also fbdev file descriptors are allowed, perhaps there are other sysfs > >> traits we can look at? > > Somewhat out of curiosity, but why do you have to overwrite all of drm? > > amdgpu seems to be able to pull their stunt off without ... > > -Daniel > > At the time we launched the standalone vmwgfx, the DRM <-> driver > interface was moving considerably more rapidly than the DRM <-> kernel > interface. I think that's still the case. Hence less work for us. Also > meant we can install the full driver stack with latest features on > fairly old VMs without backported DRM functionality. > I think this should be fine for 99% of drm usage, there may be corner cases in wierd places, but I can't point to any that really matter (maybe strace?) Acked-by: Dave Airlie <airlied at redhat.com> Dave.
