Re: [PATCH v3 1/2] dt-bindings: display: bridge: add TI TDP158

[Maxime Ripard <mripard@kernel.org>]

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On Mon, Jul 01, 2024 at 05:36:18PM GMT, Marc Gonzalez wrote:
> On 01/07/2024 15:50, Maxime Ripard wrote:
> 
> > On Thu, Jun 27, 2024 at 01:13:03PM GMT, Marc Gonzalez wrote:
> >
> >> TDP158 is an AC-coupled DVI / HDMI to TMDS level shifting Redriver.
> >> It supports DVI 1.0, HDMI 1.4b and 2.0b.
> >> It supports 4 TMDS channels, HPD, and a DDC interface.
> >> It supports dual power supply rails (1.1V on VDD, 3.3V on VCC)
> >> for power reduction. Several methods of power management are
> >> implemented to reduce overall power consumption.
> >> It supports fixed receiver EQ gain using I2C or pin strap to
> >> compensate for different lengths input cable or board traces.
> >>
> >> Features
> >>
> >> - AC-coupled TMDS or DisplayPort dual-mode physical layer input
> >> to HDMI 2.0b TMDS physical layer output supporting up to 6Gbps
> >> data rate, compatible with HDMI 2.0b electrical parameters
> >> - DisplayPort dual-mode standard version 1.1
> >> - Programmable fixed receiver equalizer up to 15.5dB
> >> - Global or independent high speed lane control, pre-emphasis
> >> and transmit swing, and slew rate control
> >> - I2C or pin strap programmable
> >> - Configurable as a DisplayPort redriver through I2C
> >> - Full lane swap on main lanes
> >> - Low power consumption (200 mW at 6Gbps, 8 mW in shutdown)
> >>
> >> https://www.ti.com/lit/ds/symlink/tdp158.pdf
> >>
> >> Signed-off-by: Marc Gonzalez <mgonzalez@freebox.fr>
> >> ---
> >>  .../bindings/display/bridge/ti,tdp158.yaml         | 51 ++++++++++++++++++++++
> >>  1 file changed, 51 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/display/bridge/ti,tdp158.yaml b/Documentation/devicetree/bindings/display/bridge/ti,tdp158.yaml
> >> new file mode 100644
> >> index 0000000000000..21c8585c3bb2d
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/display/bridge/ti,tdp158.yaml
> >> @@ -0,0 +1,51 @@
> >> +# SPDX-License-Identifier: GPL-2.0-only
> >> +%YAML 1.2
> >> +---
> >> +$id: http://devicetree.org/schemas/display/bridge/ti,tdp158.yaml#
> >> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> >> +
> >> +title: TI TDP158 HDMI to TMDS Redriver
> >> +
> >> +maintainers:
> >> +  - Arnaud Vrac <avrac@freebox.fr>
> >> +  - Pierre-Hugues Husson <phhusson@freebox.fr>
> >> +
> >> +properties:
> >> +  compatible:
> >> +    const: ti,tdp158
> >> +
> >> +  reg:
> >> +    description: I2C address of the device
> >> +
> >> +  enable-gpios:
> >> +    description: GPIO controlling bridge enable
> >> +
> >> +  vcc-supply:
> >> +    description: Power supply 3.3V
> >> +
> >> +  vdd-supply:
> >> +    description: Power supply 1.1V
> >> +
> >> +  ports:
> >> +    $ref: /schemas/graph.yaml#/properties/ports
> >> +
> >> +    properties:
> >> +      port@0:
> >> +        $ref: /schemas/graph.yaml#/properties/port
> >> +        description: Bridge input
> >> +
> >> +      port@1:
> >> +        $ref: /schemas/graph.yaml#/properties/port
> >> +        description: Bridge output
> >> +
> >> +    required:
> >> +      - port@0
> >> +      - port@1
> > 
> > The device supports DVI, HDMI or DP input, with various requirements and
> > capabilities depending on the input. Your binding doesn't address that.
> > 
> > Similarly, it can do lane-swapping, so we should probably have a
> > property to describe what mapping we want to use.
> > 
> > The i2c register access (and the whole behaviour of the device) is
> > constrained on the I2C_EN pin status, and you can't read it from the
> > device, so it's also something we need to have in the DT.
> 
> We are using the device in its default configuration.
> (Power on via OE, then it works as expected)

I know, but that doesn't really matter for a binding.

> Can we leave any additional properties to be defined by whomever needs
> them in the future?

If you can guarantee that doing so would be backward compatible, sure.
But that means being able to answer those questions with a reasonable
plan.

Maxime

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