Re: [PATCH 4/4] dt-bindings: firmware: Add Qualcomm UEFI Secure Application client

Maximilian Luz
2022-07-26T11:15:31Z

Hi,

On 7/26/22 12:17, Krzysztof Kozlowski wrote:
> On 24/07/2022 00:49, Maximilian Luz wrote:
>> Add bindings for the Qualcomm Trusted Execution Environment (TrEE) UEFI
>> Secure application (uefisecapp) client.
>>
>> Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
>> ---
>> .../firmware/qcom,tee-uefisecapp.yaml | 38 +++++++++++++++++++
>> MAINTAINERS | 1 +
>> 2 files changed, 39 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/firmware/qcom,tee-uefisecapp.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/firmware/qcom,tee-uefisecapp.yaml b/Documentation/devicetree/bindings/firmware/qcom,tee-uefisecapp.yaml
>> new file mode 100644
>> index 000000000000..9e5de1005d5c
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/firmware/qcom,tee-uefisecapp.yaml
>> @@ -0,0 +1,38 @@
>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/soc/qcom/qcom,rpmh-rsc.yaml#
>
> Does not look like you tested the bindings. Please run `make
> dt_binding_check` (see
> Documentation/devicetree/bindings/writing-schema.rst for instructions).

Sorry, first time submitting a schema. Already saw the warning of Rob's
bot and Will fix this in v2.

>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Qualcomm Trusted Execution Environment UEFI Secure Application
>> +
>> +maintainers:
>> + - Maximilian Luz <luzmaximilian@gmail.com>
>> +
>> +description: |
>> + Various Qualcomm SoCs do not allow direct access to UEFI variables. Instead,
>> + these need to be accessed via the UEFI Secure Application (uefisecapp),
>> + residing in the Trusted Execution Environment (TrEE). These bindings mark the
>> + presence of uefisecapp and allow the respective client driver to load and
>> + install efivar operations, providing the kernel with access to UEFI
>> + variables.
>> +
>> +properties:
>> + compatible:
>> + const: qcom,tee-uefisecapp
>
> Isn't this SoC-specific device? Generic compatibles are usually not
> expected.

This is essentially software (kernel driver) talking to software (in the
TrustZone), so I don't expect there to be anything SoC specific about it.

>> +
>> +required:
>> + - compatible
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> + - |
>> + firmware {
>> + scm {
>> + compatible = "qcom,scm-sc8180x", "qcom,scm";
>> + };
>> + tee-uefisecapp {
>> + compatible = "qcom,tee-uefisecapp";
>
> You did not model here any dependency on SCM. This is not full
> description of the firmware/hardware

How would I do that? A lot of other stuff also depends on SCM being
present (e.g. qcom_q6v5_pas for loading mdt files) and I don't see them
declare this in the device tree. As far as I can tell, SCM is pretty
much expected to be there at all times (i.e. can't be unloaded) and
drivers check for it when probing via qcom_scm_is_available(),
deferring probe if not.

Don't take this as an excuse as in "I want to leave that out", it's just
that I don't know how one would declare such a dependency explicitly. If
you can tell me how to fix it, I'll include that for v2.

Regards,
Max