Re: [PATCH v1 1/2] dt-bindings: display: bridge: Document Solomon SSD2825

[Conor Dooley <conor@kernel.org>]

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On Fri, Feb 14, 2025 at 08:29:22AM +0200, Svyatoslav Ryhel wrote:
> чт, 13 лют. 2025 р. о 22:34 Conor Dooley <conor@kernel.org> пише:
> >
> > On Thu, Feb 13, 2025 at 03:56:04PM +0200, Svyatoslav Ryhel wrote:
> > > Add bindings for Solomon SSD2825 MIPI master bridge chip that connects an
> > > application processor with traditional parallel LCD interface and an LCD
> > > driver with MIPI slave interface. The SSD2825 supports both parallel RGB
> > > interface and serial SPI interface.
> > >
> > > Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
> > > ---
> > >  .../display/bridge/solomon,ssd2825.yaml       | 140 ++++++++++++++++++
> > >  1 file changed, 140 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/display/bridge/solomon,ssd2825.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/display/bridge/solomon,ssd2825.yaml b/Documentation/devicetree/bindings/display/bridge/solomon,ssd2825.yaml
> > > new file mode 100644
> > > index 000000000000..cd7ff971495c
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/display/bridge/solomon,ssd2825.yaml
> > > @@ -0,0 +1,140 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/display/bridge/solomon,ssd2825.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Solomon SSD2825 RGB to MIPI-DSI bridge
> > > +
> > > +maintainers:
> > > +  - Svyatoslav Ryhel <clamor95@gmail.com>
> > > +
> > > +allOf:
> > > +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: solomon,ssd2825
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  reset-gpios: true
> > > +
> > > +  dvdd-supply:
> > > +    description: Regulator for 1.2V digital power supply.
> > > +
> > > +  avdd-supply:
> > > +    description: Regulator for 1.2V analog power supply.
> > > +
> > > +  vddio-supply:
> > > +    description: Regulator for 1.8V IO power supply.
> > > +
> > > +  spi-max-frequency:
> > > +    maximum: 1000000
> > > +
> > > +  spi-cpha: true
> > > +  spi-cpol: true
> >
> > Should these be required? Supplies should really be required too, since
> > the device probably cannot function without them?
> >
> 
> No, since spi-* define mode in which device works. If both are present
> it is mode 3, if none it is mode 0.
> 
> About supplies, device cannot work without power supply obviously, but
> often exact supplies are not known and I would like to not enforce
> someone to add random regulators just because they are mandatory.

If the device doesn't work without the supplies, the supplies should be
mandatory in the binding.

> 
> > > +  clocks:
> > > +    maxItems: 1
> > > +
> > > +  clock-names:
> > > +    const: tx_clk
> >
> > Drop the _clk, since this cannot be anything else! clock-names isn't
> > really useful when you have just one, so I'd be inclined to say remove
> > it entirely...
> >
> 
> TX_CLK is the name which datasheet refers to hence I have included
> clock name solely to have clear link between datasheet clock
> references and clock used here.

I think people will be able to make the leap between "tx_clk" and "tx".

> 
> > > +  solomon,hs-zero-delay-ns:
> > > +    description:
> > > +      HS zero delay period
> > > +    default: 133
> > > +
> > > +  solomon,hs-prep-delay-ns:
> > > +    description:
> > > +      HS prep delay period
> > > +    default: 40
> >
> > Do these two have limits? Use maximum/minimum to set them if so.
> > Cheers,
> > Conor.
> >
> 
> Datasheet does not specify limits actually, only defaults. I will try
> to calculate boundaries.

Hmm, that's interesting. I see in your driver that the eventual value
gets converted down to a u8? That should at least impose some sort of
limits I guess.

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