linux-kernel - Re: [PATCH] drm/bridge: sii902x: add support for DRM_BRIDGE_ATTACH_NO

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Date:   Thu, 25 Aug 2022 14:48:47 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Dmitry Osipenko <digetx@...il.com>, andrzej.hajda@...el.com,
        robert.foss@...aro.org, Rob Herring <robh+dt@...nel.org>,
        jernej.skrabec@...il.com, jonas@...boo.se,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Laurent.pinchart@...asonboard.com,
        Sudeep Holla <Sudeep.Holla@....com>
Subject: Re: [PATCH] drm/bridge: sii902x: add support for DRM_BRIDGE_ATTACH_NO_CONNECTOR

On Wed, Aug 17, 2022 at 3:31 PM Neil Armstrong <narmstrong@...libre.com> 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?

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.

Yours,
Linus Walleij