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

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Date:   Thu, 9 Mar 2023 10:19:04 +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 04:27, Maximilian Luz wrote:
> On 3/9/23 02:33, Dmitry Baryshkov wrote:
>> 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;
>>          }
>>
> 
> Thanks! I'll give that a try.
> 
> As I can't test this on a device that doesn't have qseecom, it would
> probably be a good idea if someone could test this on a device that has
> qcom_scm but no qseecom (if those even exist) to make sure this doesn't
> misbehave.

I could not find a vendor dts which doesn't have the qseecom device 
(checked the source trees from 3.4 to the latest revisions).

-- 
With best wishes
Dmitry