Re: [PATCH] drm/bridge: sii902x: add support for DRM_BRIDGE_ATTACH_NO_CONNECTOR

[Neil Armstrong]

On 25/08/2022 14:48, Linus Walleij wrote:
> On Wed, Aug 17, 2022 at 3:31 PM Neil Armstrong <narmstrong@xxxxxxxxxxxx> wrote:
> > On 15/08/2022 02:15, Dmitry Osipenko wrote:
> > > 08.08.2022 12:51, Neil Armstrong пишет:
> > > > On 08/08/2022 11:15, Neil Armstrong wrote:
>
> > > > > > This patch broke ARM/QEMU vexpress display because of_drm_find_bridge()
> > > > > > always fail with -EPROBE_DEFER. Reverting this patch returns display
> > > > > > back. Please fix or revert, thanks in advance.
> > > > >
> > > > > Can you share a QEMU cmdline to reproduce ?
> > > >
> > > > Actually the vexpress DT has multiple input ports instead of a single
> > > > input port at @0
> > > > and an output port at @1 like documented in the bindings:
> > > >
> > > > vexpress-v2m.dtsi#L303-L307:
> > > > ports {
> > > >       #address-cells = <1>;
> > > >       #size-cells = <0>;
> > > >
> > > >       /*
> > > >        * Both the core tile and the motherboard routes their output
> > > >        * pads to this transmitter. The motherboard system controller
> > > >        * can select one of them as input using a mux register in
> > > >        * "arm,vexpress-muxfpga". The Vexpress with the CA9 core tile is
> > > >        * the only platform with this specific set-up.
> > > >        */
> > > >       port@0 {
> > > >           reg = <0>;
> > > >           dvi_bridge_in_ct: endpoint {
> > > >               remote-endpoint = <&clcd_pads_ct>;
> > > >           };
> > > >       };
> > > >       port@1 {
> > > >           reg = <1>;
> > > >           dvi_bridge_in_mb: endpoint {
> > > >               remote-endpoint = <&clcd_pads_mb>;
> > > >           };
> > > >       };
> > > > };
> > > >
> > > > bindings:
> > > >     ports:
> > > >       $ref: /schemas/graph.yaml#/properties/ports
> > > >
> > > >       properties:
> > > >         port@0:
> > > >           $ref: /schemas/graph.yaml#/properties/port
> > > >           description: Parallel RGB input port
> > > >
> > > >         port@1:
> > > >           $ref: /schemas/graph.yaml#/properties/port
> > > >           description: HDMI output port
> > > >
> > > >         port@3:
> > > >           $ref: /schemas/graph.yaml#/properties/port
> > > >           description: Sound input port
> > > >
> > > > The patch is conform to the bindings, the DT was working but is actually
> > > > not valid.
> > >
> > > I haven't looked closely at how to fix this properly, but if we can fix
> > > it using of_machine_is_compatible("arm,vexpress") workaround in the
> > > driver, then it will be good enough at least as a temporal fix, IMO.
> >
> > If other maintainers are ok with that, it can be temporary fix until the DT gets fixed.
>
> That's fine with me, will you send a patch?

Who, me ?

> I don't know how you expect the DT to get "fixed" though.
>
> The hardware looks like this, it's maybe not the most elegant
> electronics design but it exists, so... I wrote this DT with two
> inputs, see commit f1fe12c8bf332, the code handling this
> awkward mux is part of the DRM driver, see
> drivers/gpu/drm/pl111/pl111_versatile.c function
> pl111_vexpress_clcd_init() for an idea of how it works.

The proper fix would be the other way around, adding a mux bridge before the sii902x
returning the next bridge or nothing to the right controller.

> Yours,
> Linus Walleij

Neil