linux-kernel - Re: [PATCH v5 2/4] dt-bindings: media: add Maxim MAX96714 GMSL2 Deserializer

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Date: Mon, 25 Mar 2024 14:22:16 +0100
From: Julien Massot <julien.massot@...labora.com>
To: Conor Dooley <conor@...nel.org>
Cc: linux-media@...r.kernel.org, devicetree@...r.kernel.org,
 kernel@...labora.com, linux-kernel@...r.kernel.org, mchehab@...nel.org,
 robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 sakari.ailus@....fi
Subject: Re: [PATCH v5 2/4] dt-bindings: media: add Maxim MAX96714 GMSL2
 Deserializer

Hi Conor,

Thanks for your review.
On 3/17/24 16:18, Conor Dooley wrote:
> On Wed, Mar 13, 2024 at 10:49:20AM +0100, Julien Massot wrote:
>> Add DT bindings for Maxim MAX96714 GMSL2 Deserializer.
>>
>> Signed-off-by: Julien Massot <julien.massot@...labora.com>
>> ---
>> Change since v4:
>>   - Add compatible for MAX96714 and use it as a fallback for MAX96714F
>>   - Remove extra '|' for decriptions
>>   - Reference 'i2c-gate' instead of 'i2c-controller'
>>
>> Change since v3:
>>   - Renamed file to maxim,max96714.yaml dropped the 'f' suffix
>>   - Removed mention to C-PHY since it's not supported by MAX96714 deserializers
>>   - Removed bus-type requirement on CSI endpoint since the device only support D-PHY
>>   - Removed the clock-lanes property in the dt example
>>
>> Change since v2:
>>   - remove reg description
>>   - rename enable gpio to powerdown
>>   - use generic node name: i2c, serializer, deserializer
>> ---
>>   .../bindings/media/i2c/maxim,max96714.yaml    | 176 ++++++++++++++++++
>>   1 file changed, 176 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/media/i2c/maxim,max96714.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/media/i2c/maxim,max96714.yaml b/Documentation/devicetree/bindings/media/i2c/maxim,max96714.yaml
>> new file mode 100644
>> index 000000000000..59b116092834
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/media/i2c/maxim,max96714.yaml
>> @@ -0,0 +1,176 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +# Copyright (C) 2024 Collabora Ltd.
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/media/i2c/maxim,max96714.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Maxim MAX96714 GMSL2 to CSI-2 Deserializer
>> +
>> +maintainers:
>> +  - Julien Massot <julien.massot@...labora.com>
>> +
>> +description:
>> +  The MAX96714 deserializer converts GMSL2 serial inputs into MIPI
>> +  CSI-2 D-PHY formatted output. The device allows the GMSL2 link to
>> +  simultaneously transmit bidirectional control-channel data while forward
>> +  video transmissions are in progress. The MAX96714 can connect to one
>> +  remotely located serializer using industry-standard coax or STP
>> +  interconnects. The device cans operate in pixel or tunnel mode. In pixel mode
>> +  the MAX96714 can select individual video stream, while the tunnel mode forward all
>> +  the MIPI data received by the serializer.
>> +
>> +  The GMSL2 serial link operates at a fixed rate of 3Gbps or 6Gbps in the
>> +  forward direction and 187.5Mbps in the reverse direction.
>> +  MAX96714F only supports a fixed rate of 3Gbps in the forward direction.
>> +
>> +properties:
>> +  compatible:
>> +    oneOf:
>> +      - enum:
>> +          - maxim,max96714
> 
> There's only once device here, make it const rather than enum.

Okay fixed in v6

> 
>> +      - items:
>> +          - enum:
>> +              - maxim,max96714f
>> +          - const: maxim,max96714 # fallback for 'f' variant
> 
> Drop the comment btw, it doesn't make sense given you have an enum that
> will allow for more devices and it being a fallback is obvious. That
> said, given what you told me on the last version
> | Yes there are a few differences visible to the software, for example the
> | GMSL
> | link rate since MAX96714 support 6 and 3 Gbps, while MAX96714F only
> | supports 3Gbps.
> | the registers map is the same, but a few values are not possible with
> | the 'f' version.
> I don't think your ordering here is correct. The 96714 should fall back
> to the 96714f, not the opposite that you have here, as the f is the
> version which supports fewer features.
> 
> I think this should be:
> 
> oneOf:
>    - const: maxim,max96714f
>    - items:
>        - enum:
>            - maxim,max96714
>        - const: maxim,max96714f

I just sent a v6 version with your suggestion. Indeed it makes more sense
to use max96714/7f as a fallback for the non f variant.

Best regards,
Julien