List display device names

[Emil Velikov]

On 12 November 2015 at 07:37, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> On Wed, 11 Nov 2015 22:06:12 +0000
> Emil Velikov <emil.l.velikov at gmail.com> wrote:
>
>> Hi Tom,
>>
>> On 11 November 2015 at 13:31, Tom Deseyn <tom.deseyn at gmail.com> wrote:
>> > Hi all,
>> >
>> > To configure X I need to know the display device names (e.g. DFP-0). I get
>> > these by looking at the Xorg.log. Is there a way to list these display
>> > device names which is more suitable for automation? I looked at xrandr, but
>> > I haven't found an option which outputs these names.
>> >
>> Have a look in /sys/class/drm/. If you have two GPUs there might be a
>> bit of an issue - the numbers (names) will work but are not
>> persistent, as the boot order of drm modules may change.
>
> Hi,
>
> I'm not sure /sys actually works for X and xorg.conf. The names used
> vary by the video DDX in use. E.g. modesetting driver uses different
> names than intel driver. The names used by the DRM kernel system is yet
> another thing.
>
Indeed you are correct - all the ddx iterate over the available
connectors and create the names. In my case they align as 1) the
nouveau ddx implementation aligns the kernel one and 2) I have only
one GPU.

> I have a vague recollection that DFP names might even be an NVIDIA
> proprietary driver invention that no-one else uses?
>
Spot on ! Afaict neither one of nouveau, intel and radeon (+amdgpu ?)
ddx has ever used it.

> Sorry, but I'm not aware of any better way than looking at X log or
> xrandr output. If you are configuring the kernel command line for
> video=, then looking in /sys provides the right names.
>
> I suppose if you wrote your own RandR app, you'd get the names "for
> sure".
>
Thanks for unravelling this fortunate coincidence Pekka. I would have
stayed misguided if you wasn't for you.

Emil