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

[Krzysztof Kozlowski]

On 27/06/2024 18:45, Marc Gonzalez wrote:
> 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!
> 
> Valid question.
> 
> As discussed in my brilliantly expanded commit message (:p)
> the device can be configured in various ways, either through I2C registers
> or by pin strap. We use the device in its default settings, so we don't
> touch any I2C registers, thus I'm not sure the reg property is required.

But then how would it be represented in the DT? Where / under which parent?

If this is supposed to be always in I2C bus in DT, then you always need
reg. If you could place it in other place, then your reasoning is valid
- reg is optional.

Best regards,
Krzysztof