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

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Message-ID: <324f7b6e-c72c-40aa-afe6-779345c2eade@linaro.org>
Date: Wed, 28 Feb 2024 13:18:26 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Paweł Anikiel <panikiel@...gle.com>,
 Rob Herring <robh@...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, 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 28/02/2024 12:05, Paweł Anikiel wrote:
> On Tue, Feb 27, 2024 at 3:29 PM Rob Herring <robh@...nel.org> wrote:
>>
>> On Mon, Feb 26, 2024 at 11:59:42AM +0100, Paweł Anikiel wrote:
>>> 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?
>>
>> Use the standard properties: link-frequencies and data-lanes. Those go
>> under the port(s) because they are inheritly per logical link.
> 
> The DP receiver has one input interface (a deserialized DP stream),
> and up to four output interfaces (the decoded video streams). The "max
> link rate" and "max lane count" parameters only describe the input
> interface to the receiver. However, the port(s) I am using here are
> for the output streams. They are not affected by those parameters, so
> I don't think these properties should go under the output port(s).
> 
> The receiver doesn't have an input port in the DT, because there isn't
> any controllable entity on the other side - the deserializer doesn't
> have any software interface. Since these standard properties
> (link-frequencies and data-lanes) are only defined in
> video-interfaces.yaml (which IIUC describes a graph endpoint), I can't
> use them directly in the device node.

DT describes the hardware, so where does the input come? From something,
right? Regardless if you have a driver or not. There is dp-connector
binding, if this is physical port.

> 
> Do you see a way to use these standard properties here?

Best regards,
Krzysztof