[PATCH 3/4] drm/uapi: document the USB subconnector type

[Simon Ser]

On Wednesday, August 2nd, 2023 at 21:23, Dmitry Baryshkov <dmitry.baryshkov at linaro.org> wrote:

> >> >> +	{ DRM_MODE_SUBCONNECTOR_USB,	     "USB"       }, /* DP */
> >> >
> >> > Should this be DRM_MODE_SUBCONNECTOR_USB_C and "USB-C", in case we get
> >> > another USB type later ?
> >>
> >> Hmm, which id should I use for micro-USB then? (consider anx7808,
> >> SlimPort). I thought about using DRM_MODE_SUBCONNECTOR_USB for both of
> >> them. But maybe I should add another subtype for SlimPort.
> >
> >I suppose it depends on whether userspace needs a way to differentiate
> >those. Do you have a good visibility on the userspace use cases ?
> 
> No. I'm not even sure, which userspace handles subtypes properly.

wlroots uses it for human-readable output descriptions, e.g.

    > wayland-info
    interface: 'wl_output',                                  version:  4, name: 49
    	name: DP-3
    	description: Samsung Electric Company SyncMaster HS3P505873 (DP-3 via DVI-D)

The "via DVI-D" bit comes from subconnector.

The description is displayed to the user when picking an output to screen
capture, among other things. It is helpful to users because they can better
understand why their output connected via DVI shows up as "DP".

The KMS docs describe "subconnector" to be defined as "downstream port" for DP.
Can USB-C (or USB) be seen as a DP downstream port?