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Message-ID: <64cdd9b6-dae3-f335-63a7-c20ed9b63920@quicinc.com>
Date:   Tue, 16 May 2023 11:34:01 -0700
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Subject: Re: [PATCH V6 1/3] dt-bindings: sram: qcom,imem: Add Boot Stat region
 within IMEM
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To:     Arnd Bergmann <arnd@arndb.de>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Souradeep Chowdhury <quic_schowdhu@quicinc.com>
CC:     Andy Gross <agross@kernel.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
        <devicetree@vger.kernel.org>, Sibi Sankar <quic_sibis@quicinc.com>,
        "Rajendra Nayak" <quic_rjendra@quicinc.com>
References: <cover.1683628357.git.quic_schowdhu@quicinc.com>
 <343182748e12b6a4ac57d336405c50e36fc5520c.1683628357.git.quic_schowdhu@quicinc.com>
 <CAA8EJpp2x2OEB2sg+caKmjkDYJp_NJ9mXo85FxTZr-9zRXHNhw@mail.gmail.com>
 <7d397e67-5d56-4975-98af-1ac9746c07f4@app.fastmail.com>
From:   Trilok Soni <quic_tsoni@quicinc.com>
In-Reply-To: <7d397e67-5d56-4975-98af-1ac9746c07f4@app.fastmail.com>
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On 5/16/2023 1:16 AM, Arnd Bergmann wrote:
> On Tue, May 9, 2023, at 13:35, Dmitry Baryshkov wrote:
>> On Tue, 9 May 2023 at 13:53, Souradeep Chowdhury
>> <quic_schowdhu@quicinc.com> wrote:
>>>
>>> All Qualcomm bootloaders log useful timestamp information related
>>> to bootloader stats in the IMEM region. Add the child node within
>>> IMEM for the boot stat region containing register address and
>>> compatible string.
>>
>> I might have a minor vote here. Is there any reason why you have to
>> instantiate the device from DT?
>> It looks like a software interface. Ideally software should not be
>> described in DT (e.g. this can be instantiated from imem
>> driver-to-be).
> 
> There is nothing wrong with describing firmware in DT, if that
> firmware is part of the platform, we do that for a lot of
> other bits of firmware.
> 
> However, in this specific case, many things are wrong with the
> implementation, and neither the DT binding nor the driver
> makes sense to me in its current state.
> 
>>> +  "^stats@[0-9a-f]+$":
>>> +    type: object
>>> +    description:
>>> +      Imem region dedicated for storing timestamps related
>>> +      information regarding bootstats.
>>> +
>>> +    additionalProperties: false
>>> +
>>> +    properties:
>>> +      compatible:
>>> +        items:
>>> +          - enum:
>>> +              - qcom,sm8450-bootstats
>>> +          - const: qcom,imem-bootstats
>>> +
>>> +      reg:
>>> +        maxItems: 1
> 
> If I understand this right, this "qcom,imem-bootstats"
> device serves as an indirection to store additional
> properties of the system in a memory area, but the description
> of that area is more complex than its contents, which
> makes no sense to me.
> 
> Just create a binding for a firmware node in the devicetree
> itself, and put the values in properties of that. The first
> stage firmware can still use the same interface, but the
> actual loader that assembles the DT can get it out of that
> and store it in the properties. With that done, there is also
> no need for a kernel driver, as userspace can just get the
> values from /sys/firmware/devicetree/ directly.
> 

To understand bit better here, what you are suggesting here that
application bootloader (e.g., UEFI app for Linux) can read these
boot values from the IMEM and encode them into the devicetree properties
which can be later retrieved directly from the userspace.

I am fine with this approach as well and in this case we just
need to submit the bindings document, right?

---Trilok Soni