linux-kernel - Re: [PATCH v2 8/9] media: dt-bindings: Add Intel Displayport RX IP

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Message-ID: <CAM5zL5q0oKoTMR0jSwYVAChCOJ9iKYPRFiU1vH4qDqhHALKz4w@mail.gmail.com>
Date: Mon, 26 Feb 2024 11:59:42 +0100
From: Paweł Anikiel <panikiel@...gle.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: airlied@...il.com, akpm@...ux-foundation.org, conor+dt@...nel.org, 
	daniel@...ll.ch, dinguyen@...nel.org, hverkuil-cisco@...all.nl, 
	krzysztof.kozlowski+dt@...aro.org, maarten.lankhorst@...ux.intel.com, 
	mchehab@...nel.org, mripard@...nel.org, robh+dt@...nel.org, 
	tzimmermann@...e.de, devicetree@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-media@...r.kernel.org, chromeos-krk-upstreaming@...gle.com, 
	ribalda@...omium.org
Subject: Re: [PATCH v2 8/9] media: dt-bindings: Add Intel Displayport RX IP

On Mon, Feb 26, 2024 at 10:13 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 21/02/2024 17:02, Paweł Anikiel wrote:
> > The Intel Displayport RX IP is a part of the DisplayPort Intel FPGA IP
> > Core. It implements a DisplayPort 1.4 receiver capable of HBR3 video
> > capture and Multi-Stream Transport. The user guide can be found here:
> >
> > https://www.intel.com/programmable/technical-pdfs/683273.pdf
> >
> > Signed-off-by: Paweł Anikiel <panikiel@...gle.com>
> > ---
> >  .../devicetree/bindings/media/intel,dprx.yaml | 160 ++++++++++++++++++
> >  1 file changed, 160 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/media/intel,dprx.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/media/intel,dprx.yaml b/Documentation/devicetree/bindings/media/intel,dprx.yaml
> > new file mode 100644
> > index 000000000000..31025f2d5dcd
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/media/intel,dprx.yaml
> > @@ -0,0 +1,160 @@
> > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/media/intel,dprx.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Intel DisplayPort RX IP
> > +
> > +maintainers:
> > +  - Paweł Anikiel <panikiel@...gle.com>
> > +
> > +description: |
> > +  The Intel Displayport RX IP is a part of the DisplayPort Intel FPGA IP
> > +  Core. It implements a DisplayPort 1.4 receiver capable of HBR3 video
> > +  capture and Multi-Stream Transport.
> > +
> > +  The IP features a large number of configuration parameters, found at:
> > +  https://www.intel.com/content/www/us/en/docs/programmable/683273/23-3-20-0-1/sink-parameters.html
> > +
> > +  The following parameters have to be enabled:
> > +    - Support DisplayPort sink
> > +    - Enable GPU control
> > +  The following parameters' values have to be set in the devicetree:
> > +    - RX maximum link rate
> > +    - Maximum lane count
> > +    - Support MST
> > +    - Max stream count (only if Support MST is enabled)
> > +
> > +properties:
> > +  compatible:
> > +    const: intel,dprx-20.0.1
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  intel,max-link-rate:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description: Max link rate configuration parameter
>
> Please do not duplicate property name in description. It's useless.
> Instead explain what is this responsible for.
>
> Why max-link-rate would differ for the same dprx-20.0.1? And why
> standard properties cannot be used?
>
> Same for all questions below.

These four properties are the IP configuration parameters mentioned in
the device description. When generating the IP core you can set these
parameters, which could make them differ for the same dprx-20.0.1.
They are documented in the user guide, for which I also put a link in
the description. Is that enough? Or should I also document these
parameters here?

>
> > +
> > +  intel,max-lane-count:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description: Max lane count configuration parameter
> > +
> > +  intel,multi-stream-support:
> > +    type: boolean
> > +    description: Multi-Stream Transport support configuration parameter
> > +
> > +  intel,max-stream-count:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description: Max stream count configuration parameter
> > +
> > +  port:
> > +    $ref: /schemas/graph.yaml#/properties/port
> > +    description: SST main link
>
> I don't understand why you have both port and ports. Shouldn't this be
> under ports?

I put both so that you can use the shorter port property when the
device only has one port (i.e. no MST support). It would work fine
without it. If you think that's unnecessary, I can remove it (and use
the ports property even if there is only one).