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

[Emil Velikov]

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