[PATCH libdrm] libdrm: Allow dynamic drm majors on linux

[Thomas Hellstrom]

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.

/Thomas