linux-kernel - Re: [PATCH 1/2] dt-bindings: misc: qcom,fastrpc: add qcom,assign-all-memory property

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Date:   Mon, 27 Mar 2023 16:36:27 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Dylan Van Assche <me@...anvanassche.be>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: misc: qcom,fastrpc: add
 qcom,assign-all-memory property

On 27/03/2023 16:26, Dylan Van Assche wrote:
>> Bindings are not for driver behavior.
>>
>>> Downstream does guard
>>> this with a property 'restrict-access' as well, see [1] for a
>>> random
>>> SDM845 downstream kernel. On SDM845, this property is not present,
>>> thus
>>> the IF block runs. On SDM670, this property is present, then the IF
>>> block is skipped. That's why I opt for this property to have this
>>> behaviour conditionally. I'm not sure how to explain it better
>>> though.
>>
>> Still you described driver... Please come with something more
>> hardware
>> related.
> 
> So just updating the description is enough then?
> 
> As this is all reverse engineered, I have no access to the
> documentation of FastRPC, so best effort:
> 
> """
> Mark allocated memory region accessible to remote processor.
> This memory region is used by remote processor to communicate
> when no dedicated Fastrpc context bank hardware is available 
> for remote processor.

This description does not explain here anything. The memory region is
already accessible without this property.

You described the desired Linux feature or behavior, not the actual
hardware. The bindings are about the latter, so instead you need to
rephrase the property and its description to match actual hardware
capabilities/features/configuration etc.

Remember that any arguments to downstream are not really good arguments.
Their design choices and bindings are usually totally not acceptable.
They simply embed whatever driver needs in DT - policies, system
configuration, driver behavior...

Also, Dmitry made here good point.



Best regards,
Krzysztof