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

[Dmitry Baryshkov]

On Fri, Jun 28, 2024 at 09:36:57AM GMT, Krzysztof Kozlowski wrote:
> 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.

As far as I understood, the device is connected to I2C bus, it just
doesn't need to be programmed. So I'd conclude that reg is required.

-- 
With best wishes
Dmitry