[PATCH libdrm 0/2] xf86drm: add OF_ fallback mechanism

[Lucas Stach]

Am Dienstag, den 23.10.2018, 18:28 +0100 schrieb Emil Velikov:
> On Thu, 18 Oct 2018 at 21:07, Christian Gmeiner
> > <christian.gmeiner at gmail.com> wrote:
> > 
> > Since kernel 4.17 (drm/etnaviv: remove the need for a gpu-subsystem DT
> > node) the etnaviv DRM driver doesn't have an associated DT node
> > anymore. This is technically correct, as the etnaviv device is a
> > virtual device driving multiple hardware devices.
> > 
> > Before 4.17 the userspace had access to the following information:
> > # cat /sys/dev/char/226:128/device/uevent
> > DRIVER=etnaviv
> > OF_NAME=gpu-subsystem
> > OF_FULLNAME=/gpu-subsystem
> > OF_COMPATIBLE_0=fsl,imx-gpu-subsystem
> > OF_COMPATIBLE_N=1
> > MODALIAS=of:Ngpu-subsystemT<NULL>Cfsl,imx-gpu-subsystem
> > DRIVER=imx-drm
> > OF_NAME=display-subsystem
> > OF_FULLNAME=/display-subsystem
> > OF_COMPATIBLE_0=fsl,imx-display-subsystem
> > OF_COMPATIBLE_N=1
> > 
> > Afer 4.17:
> > # cat /sys/dev/char/226:128/device/uevent
> > DRIVER=etnaviv
> > MODALIAS=platform:etnaviv
> > 
> 
> Mostly relaying what I mentioned previously [1], yet forgot to CC RobH.
> 
> - Are the OF entries in uevent part of the ABI or not? Can we have that
> documented anywhere?
> 
> There are very few mentions in the official kernel doc - Documentation/ABI/
> Obviously it doesn't mention anything OF_* but it neither does DRIVER
> or MODALIAS. Yet if we change those $world will break ;-)

The OF node has never been part of the etnaviv UABI, simply due to the
fact that it's still possible to instantiate the etnaviv driver from a
platform file, instead of a devicetree node.

> 
> - How can we distinguish in the (perhaps hypothetical) case when
> there's two or more etnaviv devices?

Why not simply use the DRM minor? All you need is an arbitrary handle
to grab the right instance.

Regards,
Lucas