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

[Marc Gonzalez]

On 27/06/2024 18:25, Conor Dooley wrote:

> On Thu, Jun 27, 2024 at 01:13:03PM +0200, 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 at 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 at freebox.fr>
>> +  - Pierre-Hugues Husson <phhusson at freebox.fr>
>> +
>> +properties:
>> +  compatible:
>> +    const: ti,tdp158
>> +
>> +  reg:
>> +    description: I2C address of the device
> 
> Is reg not required? How do you communicate with the device if the i2c
> bus is not connected? Is the enable GPIO enough to operate it in some
> situations?
> 
> Otherwise this looks good to me, but given Maxime commented about the
> complexity of the device, I'm probably out of my depth!

Hello Conor,

A cycle has been detected:
Above, you defer to Maxime.
Yet later, he wrote:
"DT maintainers have required that reg is always present"


I propose we NOT mark the "reg" property as required.
(Thus, keep the binding as proposed in v3.)

Rationale:

- The device can be statically configured by pin straps,
in which case it is NOT connected to an I2C bus.

- Even if the device IS connected to an I2C bus,
no I2C accesses are required if the default configuration
meets the ODM's needs.

Is that OK with you? Can I get your Amen?

Regards