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

From: Simon Ser
Date: Thu Aug 03 2023 - 11:43:43 EST

On Thursday, August 3rd, 2023 at 17:36, Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> wrote:

> On Thu, 3 Aug 2023 at 18:31, Simon Ser contact@xxxxxxxxxxx wrote:
> > On Thursday, August 3rd, 2023 at 17:22, Simon Ser contact@xxxxxxxxxxx wrote:
> >
> > > 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?
> >
> > To expand on this a bit: I'm wondering if we're mixing apples and
> > oranges here. The current values of "subconnector" typically describe
> > the lower-level protocol tunneled inside DP. For instance, VGA can be
> > tunneled inside the DP cable when using DP → VGA adapter.
> My opinion hasn't changed: I think this should be the USB connector
> with proper DP / DVI / HDMI / etc. subconnector type (or lack of it).
> In the end, the physical connector on the side of laptop is USB-C.

- Even if the connector is USB-C, the protocol used for display is
still DP. There's also the case of Thunderbolt.
- This is inconsistent with existing drivers. i915 and amdgpu expose
DP ports for their USB-C ports. Changing that isn't possible without
causing user-space regressions (compositor config files use the
connector type).