linux-kernel - Re: [PATCH 2/5] arm64: dts: qcom: sdm845-db845c-navigation-mezzanine: fix ov7251 lane properties

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Message-ID: <e9e8e34b-cd6a-41d8-a267-3b9336e3ca24@linaro.org>
Date: Wed, 4 Dec 2024 15:30:19 +0200
From: Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>
To: neil.armstrong@...aro.org, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, cros-qcom-dts-watchers@...omium.org,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] arm64: dts: qcom: sdm845-db845c-navigation-mezzanine:
 fix ov7251 lane properties

On 12/4/24 15:16, neil.armstrong@...aro.org wrote:
> On 04/12/2024 14:10, Vladimir Zapolskiy wrote:
>> On 12/4/24 14:16, Neil Armstrong wrote:
>>> On 04/12/2024 12:05, Dmitry Baryshkov wrote:
>>>> On Wed, Dec 04, 2024 at 11:56:54AM +0100, Neil Armstrong wrote:
>>>>> Bindings documents data-lanes as a single entry with a separate
>>>>> clock-lanes property, but DT uses 2 entries in data-lanes.
>>>>>
>>>>> This would suggest clock-lanes is missing, fix the DT using the
>>>>> bindings example.
>>>>>
>>>>> This fixes:
>>>>> sdm845-db845c-navigation-mezzanine.dtso: camera@60: port:endpoint:data-lanes: [0, 1] is too long
>>>>>      from schema $id: http://devicetree.org/schemas/media/i2c/ovti,ov7251.yaml#
>>>>>
>>>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>>>>> ---
>>>>>     arch/arm64/boot/dts/qcom/sdm845-db845c-navigation-mezzanine.dtso | 3 ++-
>>>>>     1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/arm64/boot/dts/qcom/sdm845-db845c-navigation-mezzanine.dtso b/arch/arm64/boot/dts/qcom/sdm845-db845c-navigation-mezzanine.dtso
>>>>> index 0a87df806cafc8e726aacc07a772ca478d0ee3df..5a16f4c2b346b314af3d614266e1ca034057e643 100644
>>>>> --- a/arch/arm64/boot/dts/qcom/sdm845-db845c-navigation-mezzanine.dtso
>>>>> +++ b/arch/arm64/boot/dts/qcom/sdm845-db845c-navigation-mezzanine.dtso
>>>>> @@ -115,7 +115,8 @@ camera@60 {
>>>>>             port {
>>>>>                 ov7251_ep: endpoint {
>>>>> -                data-lanes = <0 1>;
>>>>> +                clock-lanes = <1>;
>>>>> +                data-lanes = <0>;
>>>>
>>>> Is it really this way or the other way around, clock = <0>, data = <1>?
>>>
>>> No idea actually, on the schematics the lanes from the DB845 are :
>>>
>>> CSI0_P/N -> OV7251_CSI3_LANE0_P/N -> MIPI_CSI3_LANE0_P -> SoC
>>> and
>>> CLKP/N -> OV7251_CSI3_CLK_P/N -> MIPI_CSI3_CLK_P/N -> SoC
>>>
>>> So I assume the data-lane is 0, for clock-lane I just used
>>> the example, but I found nothing in the code using those assignments
>>>
>>
>> It's a sensor property, and OV7251 sensor has the non-selectable clock lane.
>>
>> If it's technically acceptable, I would rather suggest to deprecate and
>> remove "clock-lanes" property and hard-code "data-lanes" value to <1>.
> 
> 
> Ok indeed while looking at the OV7251 sensor datasheet, there's a single
> fixed data lane and a single fixed clock lane, so on the sensor side we
> can't select anything but how would we define lane0 is used on the SoC side ?

It's done right in the common way, there are clock-lanes and data-lanes
properties on the ISP endpoint side.

>>
>> By the way, this particular device tree bindings miss bus-type property,
>> it could be either MIPI or LVDS serial output.
>>

-- 
Best wishes,
Vladimir