linux-kernel - Re: [PATCH] dt-bindings: firmware: Add documentation for qcom,platform-parts-info

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Message-ID: <fbfc6e8d-dd6a-ee1d-a62a-d076470db18b@linaro.org>
Date:   Mon, 4 Sep 2023 11:32:57 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Naman Jain <quic_namajain@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc:     linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, quic_pkondeti@...cinc.com,
        quic_kaushalk@...cinc.com, quic_rohiagar@...cinc.com,
        kernel@...cinc.com
Subject: Re: [PATCH] dt-bindings: firmware: Add documentation for
 qcom,platform-parts-info

On 04/09/2023 10:38, Naman Jain wrote:
> 
> On 9/1/2023 12:52 PM, Krzysztof Kozlowski wrote:
>> On 01/09/2023 08:02, Naman Jain wrote:
>>> Add documentation to describe device tree bindings for QCOM's
>>> platform-parts-info node. Firmware populates these nodes to pass the
>>> information to kernel regarding the subset of hardware blocks
>>> and features like Camera, Modem, Display present in a product.
>>>
>>> This is to support that the same software image runs seamlessly on
>>> different platforms where one or more HW blocks are not supported or
>>> if some sub parts for a particular block are not supported.
>>>
>>> Purpose of these definitions is to allow clients to know about this,
>>> and thus, handle these cases gracefully.
>> Whether camera is or is not supported, is defined by presence of camera
>> node or by its status field.
>>
>> Existing firmware (e.g. U-Boot) is also doing this - patching DTS when
>> needed.
>>
>> I do not think introducing some parallel way makes any sense, so no,
>> that's not the way to do it.
>>
>> Best regards,
>> Krzysztof
> 
> 
> Thanks Krzysztof for reviewing the patch. I think for telling whether 
> the Camera HW block is not
> supported / not present, firmware can either remove the device tree 
> node, or change its status
> to disabled, so that is fine.
> With this patch, I was trying to address the use case, where Camera is 
> supported but certain features
> of that particular Camera are not supported, due to dependent HW blocks 
> not present, or due to
> product decision to not support it. We wanted to avoid the firmware to 
> have this overhead of knowing
> what these individual bits mean and thus, disable few of the HW blocks 
> that are supposed to be
> disabled. And this is applicable for each of these HW blocks.

What is and what is not supported by camera, is obvious from the
compatible and you do not need this patch.

> 
> For example, we can know from 32 bits provided for modem, if 3G/4G/5G is 
> supported or not on a
> platform.

Again, compatible-dependent.

> That is decided based on presence/absence of certain HW 
> blocks, but it may or may not be as
> simple as disabling a particular DT node.
> Basically we wanted to defer it to the subsystem drivers, to do whatever 
> they like with this
> information on sub-parts that are available.
> 
> Will rephrase my commit message to make it clearer, but would like to 
> hear your thoughts on this first.

Sorry, no, such node is not the solution.

Best regards,
Krzysztof