[PATCH v15 04/10] dt-bindings: display: bridge: anx7625: Add mode-switch support

[Stephen Boyd]

Quoting Stephen Boyd (2023-04-13 17:22:46)
> Quoting Pin-yen Lin (2023-04-13 02:50:44)
> >
> > Actually the `mode-switch` property here is mainly because
> > `fwnode_typec_mux_get`[1] and `typec_mux_match`[2] only return matches
> > when the property is present. I am not sure what side effects would be
> > if I remove the ID-matching condition in `typec_mux_match`, so I added
> > the property here.
> >
> > Is it feasible to remove the `mode-switch` property here given the
> > existing implementation of the Type-C framework?
>
> Omitting the mode-switch property would require changes to the type-c
> framework.
>
> I'm wondering if we can have this anx driver register mode switches for
> however many endpoints exist in the output port all the time when the
> aux-bus node doesn't exist. Then the type-c framework can walk from the
> usb-c-connector to each connected node looking for a device that is both
> a drm_bridge and a mode-switch. When it finds that combination, it knows
> that the mode-switch has been found. This hinges on the idea that a
> device that would have the mode-switch property is a drm_bridge and
> would register a mode-switch with the type-c framework.
>
> It may be a little complicated though, because we would only register
> one drm_bridge for the input to this anx device. The type-c walking code
> would need to look at the graph endpoint, and find the parent device to
> see if it is a drm_bridge.

I've been thinking more about this. I think we should only have the
'mode-switch' property possible when the USB input pins (port at 2) are
connected and the DPI input pins are connected (port at 0). Probably you
don't have that case though?

In your case, this device should register either one or two drm_bridges
that connect to whatever downstream is actually muxing the 2 DP lanes
with the USB SS lanes onto the usb-c-connector. If that is the EC for
ChromeOS, then the EC should have a binding that accepts some number of
input ports for DP. The EC would act as a drm_bridge, or in this case
probably two bridges, and also as two type-c switches for each
drm_bridge corresponding to the usb-c-connector nodes. When DP is on the
cable, the type-c switch/mux would signal to the drm_bridge that the
display is 'connected' via DRM_BRIDGE_OP_DETECT and struct
drm_bridge_funcs::detect(). Then the drm_bridge in this anx part would
implement struct drm_bridge_funcs::atomic_enable() and configure the
crosspoint switch the right way depending on the reg property of the
output node in port at 1.

Because you don't have the part that implements the orientation-switch,
you don't need to implement the code for it. I think simply adding
support in the binding for mode-switch and orientation-switch if this is
directly wired to a usb-c-connector should be sufficient. Those
properties would be at the top-level and not part of the graph binding.