Render only DRM devices

[Christian König]

Am 11.10.22 um 13:37 schrieb Simon Ser:
> On Tuesday, October 11th, 2022 at 13:04, Christian König <ckoenig.leichtzumerken at gmail.com> wrote:
>
>> we already have quite a bunch of devices which are essentially render
>> only and don't expose any connectors or more general display functionality.
>>
>> Just recently I ran into a case where an older X/DDX combination
>> caused problems for such a device so I looked a bit into the
>> possibility to allow drivers to disable the primary node and only
>> expose the render node.
>>
>> It turned out that this effectively hides the device from X, but
>> OpenGL and Vulkan can still use it perfectly fine.
>>
>> The only crux is that this is checked so early in the initialization
>> that drivers don't have an opportunity to update their
>> dev->driver_features. So we will always need a separate drm_driver
>> structure for render only devices.
> Typically render-only devices still expose a primary node, but don't
> expose any KMS resources on it. See drmIsKMS() in libdrm.
>
> Primary nodes could still be used by older user-space for rendering with
> legacy DRM authentication.

Yeah, and that's exactly what we try to avoid :)

Cheers,
Christian.