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Message-ID: <Y+InK8qF0Izlv6s6@pendragon.ideasonboard.com>
Date: Tue, 7 Feb 2023 12:25:47 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Pin-yen Lin <treapking@...omium.org>
Cc: Rob Herring <robh@...nel.org>,
Andrzej Hajda <andrzej.hajda@...el.com>,
Neil Armstrong <neil.armstrong@...aro.org>,
Robert Foss <robert.foss@...aro.org>,
Jonas Karlman <jonas@...boo.se>,
Jernej Skrabec <jernej.skrabec@...il.com>,
David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Nicolas Boichat <drinkcat@...omium.org>,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
Hsin-Yi Wang <hsinyi@...omium.org>,
dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 1/2] dt-bindings: display: bridge: Add GPIO display
mux binding
On Tue, Feb 07, 2023 at 06:07:44PM +0800, Pin-yen Lin wrote:
> On Wed, Jan 18, 2023 at 4:17 AM Rob Herring wrote:
> > On Mon, Jan 16, 2023 at 07:08:19PM +0800, Pin-yen Lin wrote:
> > > From: Nicolas Boichat <drinkcat@...omium.org>
> > >
> > > Add bindings for Generic GPIO mux driver.
> > >
> > > Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> > > Signed-off-by: Pin-yen Lin <treapking@...omium.org>
> > > ---
> > >
> > > Changes in v2:
> > > - Referenced existing dt-binding schemas from graph.yaml
> > > - Added ddc-i2c-bus into the bindings
> > >
> > > .../bindings/display/bridge/gpio-mux.yaml | 95 +++++++++++++++++++
> > > 1 file changed, 95 insertions(+)
> > > create mode 100644 Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml b/Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml
> > > new file mode 100644
> > > index 000000000000..da29ba078f05
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml
> > > @@ -0,0 +1,95 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/display/bridge/gpio-mux.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Generic display mux (1 input, 2 outputs)
> > > +
> > > +maintainers:
> > > + - Nicolas Boichat <drinkcat@...omium.org>
> > > +
> > > +description: |
> > > + This bindings describes a simple display (e.g. HDMI) mux, that has 1
> > > + input, and 2 outputs. The mux status is controlled by hardware, and
> > > + its status is read back using a GPIO.
> > > +
> > > +properties:
> > > + compatible:
> > > + const: gpio-display-mux
> > > +
> > > + detect-gpios:
> > > + maxItems: 1
> > > + description: GPIO that indicates the active output
> >
> > What are we detecting? That implies an input, but this is selecting the
> > output path, right? Or what does 'mux status is controlled by hardware'
> > mean exactly? Something else? That does not sound very generic.
>
> The GPIO (or any kind of MUX) is an input that indicates where the
> output should go. The actual "output selection" procedure is done in
> the driver. That is, the driver monitors this GPIO and selects the
> output path accordingly. In our use case, the GPIO is reported by the
> embedded controller on the device.
>
> [1] listed other similar bridges that can leverage this driver, so we
> called this driver "generic".
>
> [1]: https://lore.kernel.org/all/CAJMQK-jGw8kJFNjoHjeZUL+3NCiOS2hgGERnAnMwNsL_cm_J=Q@mail.gmail.com/
>
> > In any case, we have a common mux binding so any kind of mux control
> > could be used here, not just GPIO. Then you can make this just a generic
> > display mux.
>
> Thanks for sharing this, I'll update the binding in the next version.
>
> > > +
> > > + ddc-i2c-bus:
> > > + description: phandle link to the I2C controller used for DDC EDID probing
> > > + $ref: /schemas/types.yaml#/definitions/phandle
> >
> > This belongs in the connector node(s).
>
> The HDMI bridge before the MUX doesn't (and doesn't have to) know that
> its next bridge is a MUX. We put it here so that the HDMI bridge can
> parse the phandle and get the bus node.
How does that work, does the HDMI encoder driver parse the ddc-i2c-bus
property of the next DT node in the OF graph ?
> > > +
> > > + ports:
> > > + $ref: /schemas/graph.yaml#/properties/ports
> > > +
> > > + properties:
> > > + port@0:
> > > + $ref: /schemas/graph.yaml#/properties/port
> > > + description: |
> > > + Video port for input.
> > > +
> > > + port@1:
> > > + $ref: /schemas/graph.yaml#/properties/port
> > > + description: |
> > > + 2 video ports for output.
> > > + The reg value in the endpoints matches the GPIO status: when
> > > + GPIO is asserted, endpoint with reg value <1> is selected.
> > > +
> > > + required:
> > > + - port@0
> > > + - port@1
> > > +
> > > +required:
> > > + - compatible
> > > + - detect-gpios
> > > + - ports
> > > +
> > > +unevaluatedProperties: false
> > > +
> > > +examples:
> > > + - |
> > > + #include <dt-bindings/gpio/gpio.h>
> > > + hdmi_mux: hdmi_mux {
> > > + compatible = "gpio-display-mux";
> > > + detect-gpios = <&pio 36 GPIO_ACTIVE_HIGH>;
> > > + pinctrl-names = "default";
> > > + pinctrl-0 = <&hdmi_mux_pins>;
> > > + ddc-i2c-bus = <&hdmiddc0>;
> > > +
> > > + ports {
> > > + #address-cells = <1>;
> > > + #size-cells = <0>;
> > > +
> > > + port@0 { /* input */
> > > + reg = <0>;
> > > +
> > > + hdmi_mux_in: endpoint {
> > > + remote-endpoint = <&hdmi0_out>;
> > > + };
> > > + };
> > > +
> > > + port@1 { /* output */
> > > + reg = <1>;
> > > +
> > > + #address-cells = <1>;
> > > + #size-cells = <0>;
> > > +
> > > + hdmi_mux_out_anx: endpoint@0 {
> > > + reg = <0>;
> > > + remote-endpoint = <&dp_bridge_in>;
> > > + };
> > > +
> > > + hdmi_mux_out_hdmi: endpoint@1 {
> > > + reg = <1>;
> > > + remote-endpoint = <&hdmi_connector_in>;
> > > + };
> > > + };
> > > + };
> > > + };
--
Regards,
Laurent Pinchart
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