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

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Date:   Thu, 9 Mar 2023 03:33:00 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...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 09/03/2023 00:44, 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...
> 
>> 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.
> 
>> Nodes with only a compatible string are usually just an abuse of DT to
>> instantiate some driver.
> 
> If you or anyone here has any idea on how to discover the presence of
> this, please feel free to let me know and I'd be happy to implement
> that. Until then, I unfortunately don't see any other way of dealing
> with this.

You can probably try requesting QSEECOM version. According to msm-3.18:

         uint32_t feature = 10;

         rc = qseecom_scm_call(6, 3, &feature, sizeof(feature),
                 &resp, sizeof(resp));
         pr_info("qseecom.qsee_version = 0x%x\n", resp.result);
         if (rc) {
                 pr_err("Failed to get QSEE version info %d\n", rc);
                 goto exit_del_cdev;
         }


-- 
With best wishes
Dmitry