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

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Date: Wed, 21 Feb 2024 17:30:57 +0100
From: Paweł Anikiel <panikiel@...gle.com>
To: Conor Dooley <conor@...nel.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 8/9] media: dt-bindings: Add Intel Displayport RX IP

On Thu, Feb 15, 2024 at 6:26 PM Conor Dooley <conor@...nel.org> wrote:
>
> Yo,
>
> On Mon, Feb 12, 2024 at 01:13:22PM +0000, 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 | 125 ++++++++++++++++++
> >  1 file changed, 125 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..3ed37e0a4a94
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/media/intel,dprx.yaml
> > @@ -0,0 +1,125 @@
> > +# 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>
> > +
> > +properties:
> > +  compatible:
> > +    const: intel,dprx
>
> Please version this compatible, given that is it for an FPGA IP.
> I could not find an example of another intel IP that had versioning, but
> there's plenty of xilinx stuff you can get inspiration from.

The IP has had a few different revisions, so I decided to just use the
"IP version" which is 20.0.1 for the version this driver is targeting.

>
> > +  reg:
> > +    items:
> > +      - description: core registers
> > +      - description: irq registers
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  intel,has-mst:
>
> Mostly this looks fine, but this property drew my eye.
> Firstly, I'd probably call this "intel,multi-stream-support" rather than
> "intel,has-mst".

Sure,

>
> > +    type: boolean
> > +    description: The device supports Multi-Stream Transport
>
> Secondly, there are many many configuration parameters for this IP,
> but you have chosen to document just one.
> Are all other configuration parameters currently in their default
> states or ignored by the driver? If not, please at least document all
> configuration settings that you rely on - for example the max stream
> count or audio packet encoding.

I looked at all the parameters listed in the user guide, and most of
them don't affect the driver. I listed the ones which are required,
and added support for the remaining ones in v2.

>
> > +
> > +  port:
> > +    $ref: /schemas/graph.yaml#/properties/port
> > +    description: SST main link
> > +
> > +  ports:
> > +    $ref: /schemas/graph.yaml#/properties/ports
> > +
> > +    properties:
> > +      port@0:
> > +        $ref: /schemas/graph.yaml#/properties/port
> > +        description: MST virtual channel 0 or SST main link
> > +
> > +      port@1:
> > +        $ref: /schemas/graph.yaml#/properties/port
> > +        description: MST virtual channel 1
> > +
> > +      port@2:
> > +        $ref: /schemas/graph.yaml#/properties/port
> > +        description: MST virtual channel 2
> > +
> > +      port@3:
> > +        $ref: /schemas/graph.yaml#/properties/port
> > +        description: MST virtual channel 3
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - interrupts
> > +
> > +allOf:
> > +  - if:
> > +      required:
> > +        - intel,has-mst
> > +    then:
> > +      required:
> > +        - ports
> > +    else:
> > +      required:
> > +        - port
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    dprx@...62000 {
>
> "dprx" isn't a class of device, please try to use a generic node name
> here.

I couldn't find anything in the DT spec or any other similar examples,
so I chose dp-receiver.