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

[Maximilian Luz <luzmaximilian@gmail.com>]

On 5/2/23 10:38, Sudeep Holla wrote:
> On Thu, Mar 09, 2023 at 03:27:01AM +0100, 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.
>>
> 
> TBH, this has been going in round for quite sometime. We have been asking
> you to depend on existing platform compatible + a query or a check on the
> version. Since you do have a platform that is working, we can start making
> it min "qseecom.qsee_version" supported and then adjust the version based
> on the testing or the requirement. What do you think ?
Sure, I will add a minimum version check to that.

Regards,
Max