linux-kernel - Re: [PATCH v3 3/4] dt-bindings: firmware: Add Qualcomm QSEECOM interface

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Date:   Tue, 2 May 2023 10:31:33 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Maximilian Luz <luzmaximilian@...il.com>,
        Rob Herring <robh@...nel.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Johan Hovold <johan@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Steev Klimaszewski <steev@...i.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 3/4] dt-bindings: firmware: Add Qualcomm QSEECOM
 interface

On 08/03/2023 23:44, Maximilian Luz wrote:
> On 3/8/23 23:16, Rob Herring wrote:
>> On Sun, Mar 05, 2023 at 03:21:18AM +0100, Maximilian Luz wrote:
>>> Add bindings for the Qualcomm Secure Execution Environment interface
>>> (QSEECOM).
>>
>> Pretty sure I already asked, but no answer in the commit message. Why do
>> we need this? You've already declared the platform supports SCM calls
>> with "qcom,scm". Why can't you probe whether you have QSEECOM or not? DT
>> is for non-discoverable h/w we are stuck with.
> 
> Yes, you've asked this before but I can only repeat what I've written in
> my last response to your question: I am not aware of any way to properly
> discover the interface at runtime from software.
> 
> If it makes you happy, I can put this in the commit message as well...

Yes, please, because commit msg should answer to "why we are doing
this", when this is not obvious. If the reviewer asks the same twice it
means it is not obvious.

> 
>> Why is software made non-discoverable too?
> 
> Please direct that question at the Qualcomm guys who actually designed
> that interface. I can't give you an answer to that, and I'm not all that
> happy about this either.
> 
> To reiterate: I've reverse engineered this based on the Windows driver.
> The Windows driver loads on an ACPI HID and it doesn't use any function
> to check/verify whether the interface is actually present. Adding a DT
> entry is the straight-forward adaption to having a HID in ACPI.


Best regards,
Krzysztof