Re: [RFC PATCH 1/6] dt-bindings: display/bridge: Add binding for input mux bridge

From: "Guido Günther" <agx@sigxcpu.org>
To: Rob Herring <robh@kernel.org>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Shawn Guo <shawnguo@kernel.org>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Fabio Estevam <festevam@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Sam Ravnborg <sam@ravnborg.org>,
	Anson Huang <Anson.Huang@nxp.com>,
	Leonard Crestez <leonard.crestez@nxp.com>,
	Lucas Stach <l.stach@pengutronix.de>, Peng Fan <peng.fan@nxp.com>,
	Robert Chiras <robert.chiras@nxp.com>,
	dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH 1/6] dt-bindings: display/bridge: Add binding for input mux bridge
Date: Sat, 30 May 2020 15:26:34 +0200	[thread overview]
Message-ID: <20200530132634.GA3337@bogon.m.sigxcpu.org> (raw)
In-Reply-To: <20200528194804.GA541078@bogus>

Hi Rob,
On Thu, May 28, 2020 at 01:48:04PM -0600, Rob Herring wrote:
> On Fri, May 15, 2020 at 03:12:10PM +0200, Guido Günther wrote:
> > The bridge allows to select the input source via a mux controller.
> > 
> > Signed-off-by: Guido Günther <agx@sigxcpu.org>
> > ---
> >  .../display/bridge/mux-input-bridge.yaml      | 123 ++++++++++++++++++
> >  1 file changed, 123 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/display/bridge/mux-input-bridge.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/display/bridge/mux-input-bridge.yaml b/Documentation/devicetree/bindings/display/bridge/mux-input-bridge.yaml
> > new file mode 100644
> > index 000000000000..4029cf63ee5c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/display/bridge/mux-input-bridge.yaml
> > @@ -0,0 +1,123 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/display/bridge/mux-input-bridge.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: DRM input source selection via multiplexer
> 
> DRM is not a hardware thing.

I thought about naming the mux pixel-input-mux (input-mux sounding too
generic) but then i hit rockchip-drm and went for that name.  The
binding itself is not a drm thing in itself it really aims to model how
the mux is placed in the 'display pipeline' of the SoC (as Laurent
explained). Should I go with pixel-input-mux?

> The graph binding is already designed to support muxing. Generally, 
> multiple endpoints on an input node is a mux. So either the device with 
> the input ports knows how to select the input, or you just need a 
> mux-control property for the port to have some other device implement 
> the control.

A mux control property is how it's modeled at the moment but that is
very SoC specific.

> You could do it like you have below. That would be appropriate if 
> there's a separate h/w device controlling the muxing. Say for example 
> some board level device controlled by i2c.

It's a different part of the SoC that lives in a register range very
separate (iomuxc_gpr) from MIPI/DSI (nwl). Does that qualify?

Cheers,
 -- Guido

> 
> Rob
> 