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

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Message-ID: <eb7fc499-d60f-4a3f-8279-1c9de19c2328@linaro.org>
Date: Wed, 4 Dec 2024 14:16:00 +0100
From: neil.armstrong@...aro.org
To: Vladimir Zapolskiy <vladimir.zapolskiy@...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 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 ?

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