linux-kernel - Re: [PATCH 1/2] media: dt-bindings: media: camss: Restrict bus-type property

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Message-ID: <d7e3076e-5b32-4ab8-afe8-f52458769f23@linaro.org>
Date: Fri, 13 Dec 2024 11:34:24 +0000
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Luca Weiss <luca.weiss@...rphone.com>,
 Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
 Krzysztof Kozlowski <krzk@...nel.org>
Cc: Robert Foss <rfoss@...nel.org>, Todor Tomov <todor.too@...il.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Barnabas Czeman <barnabas.czeman@...nlining.org>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>,
 Caleb Connolly <caleb.connolly@...aro.org>, David Heidelberg
 <david@...t.cz>, ~postmarketos/upstreaming@...ts.sr.ht,
 phone-devel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-media@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] media: dt-bindings: media: camss: Restrict bus-type
 property

On 13/12/2024 11:24, Luca Weiss wrote:
> On Fri Dec 13, 2024 at 11:50 AM CET, Vladimir Zapolskiy wrote:
>> On 12/13/24 11:34, Krzysztof Kozlowski wrote:
>>> On Mon, Dec 09, 2024 at 01:01:05PM +0100, Luca Weiss wrote:
>>>> The CSIPHY of Qualcomm SoCs support both D-PHY and C-PHY standards for
>>>> CSI-2, but not any others so restrict the bus-type property describing
>>>> this to the supported values.
>>>>
>>>> The only exception here is MSM8916 which only supports D-PHY. C-PHY was
>>>> introduced with newer SoCs.
>>>>
>>>> Do note, that currently the Linux driver only supports D-PHY.
>>>>
>>>> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
>>>> ---
>>>>    .../bindings/media/qcom,msm8916-camss.yaml         |  8 ++++++
>>>>    .../bindings/media/qcom,msm8953-camss.yaml         | 15 +++++++++++
>>>>    .../bindings/media/qcom,msm8996-camss.yaml         | 20 +++++++++++++++
>>>>    .../bindings/media/qcom,sc8280xp-camss.yaml        | 20 +++++++++++++++
>>>>    .../bindings/media/qcom,sdm660-camss.yaml          | 20 +++++++++++++++
>>>>    .../bindings/media/qcom,sdm845-camss.yaml          | 20 +++++++++++++++
>>>>    .../bindings/media/qcom,sm8250-camss.yaml          | 30 ++++++++++++++++++++++
>>>>    7 files changed, 133 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/media/qcom,msm8916-camss.yaml b/Documentation/devicetree/bindings/media/qcom,msm8916-camss.yaml
>>>> index 9cc0a968a401836814560c1af3ee84d946500b4f..3de2a3d2b5b761106975aab65ff614b2ef579ef5 100644
>>>> --- a/Documentation/devicetree/bindings/media/qcom,msm8916-camss.yaml
>>>> +++ b/Documentation/devicetree/bindings/media/qcom,msm8916-camss.yaml
>>>> @@ -94,6 +94,10 @@ properties:
>>>>                    minItems: 1
>>>>                    maxItems: 4
>>>>    
>>>> +              bus-type:
>>>> +                enum:
>>>> +                  - 4 # MEDIA_BUS_TYPE_CSI2_DPHY
>>>> +
>>>>                required:
>>>>                  - data-lanes
>>>>    
>>>> @@ -113,6 +117,10 @@ properties:
>>>>                    minItems: 1
>>>>                    maxItems: 4
>>>>    
>>>> +              bus-type:
>>>> +                enum:
>>>> +                  - 4 # MEDIA_BUS_TYPE_CSI2_DPHY
>>>> +
>>
>> But is it really needed to specify the single supported bus-type?
>>
>> I believe it is not, at least it's not ever done for other media devices
>> like sensors.
> 
> Through video-interfaces.yaml 'bus-type' is already allowed but not
> restricted to the values that actually make any sense on such hardware,
> so in my opinion this makes sense to have here.
This is additive not prescriptive.

New additions should include this bus-type number as we will need it 
when we add CPHY support and the subsequently move to the PHY API for 
CAMSS PHYs.

So still in favour of this amendment.

---
bod