linux-kernel - Re: [PATCH 05/11] dt-bindings: document the Qualcomm TEE Shared Memory Bridge

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Message-ID: <3f7f6427-51eb-a251-f8dd-f7922b9fcfd7@linaro.org>
Date:   Wed, 30 Aug 2023 16:31:00 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Alex Elder <elder@...aro.org>,
        Srini Kandagatla <srinivas.kandagatla@...aro.org>,
        kernel@...cinc.com, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 05/11] dt-bindings: document the Qualcomm TEE Shared
 Memory Bridge

On 30/08/2023 15:48, Bartosz Golaszewski wrote:
> On Tue, 29 Aug 2023 at 11:30, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>>
>> On 29.08.2023 10:02, Krzysztof Kozlowski wrote:
>>> On 28/08/2023 21:25, Bartosz Golaszewski wrote:
>>>> Add Device Tree bindings for Qualcomm TEE Shared Memory Brige - a
>>>> mechanism that allows sharing memory buffers between trustzone and the
>>>> kernel.
>>>
>>> Subject prefix:
>>> dt-bindings: firmware:
>>>
>>>
>>>
>>>>
>>>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>>>> ---
>>>>  .../bindings/firmware/qcom,shm-bridge.yaml    | 36 +++++++++++++++++++
>>>>  1 file changed, 36 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/firmware/qcom,shm-bridge.yaml
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/firmware/qcom,shm-bridge.yaml b/Documentation/devicetree/bindings/firmware/qcom,shm-bridge.yaml
>>>> new file mode 100644
>>>> index 000000000000..f660962b7b86
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/firmware/qcom,shm-bridge.yaml
>>>> @@ -0,0 +1,36 @@
>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>> +%YAML 1.2
>>>> +---
>>>> +$id: http://devicetree.org/schemas/firmware/qcom,shm-bridge.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: QCOM Shared Memory Bridge
>>>> +
>>>> +description: |
>>>
>>> Do not need '|' unless you need to preserve formatting.
>>>
>>>> +  Qualcomm TEE Shared Memory Bridge allows sharing limited areas of kernel's
>>>> +  virtual memory with the trustzone in order to avoid mapping the entire RAM.
>>>> +
>>>> +maintainers:
>>>> +  - Bjorn Andersson <andersson@...nel.org>
>>>> +  - Konrad Dybcio <konrad.dybcio@...aro.org>
>>>> +  - Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    items:
>>>> +      - enum:
>>>> +          - qcom,shm-bridge-sa8775p
>>>> +          - qcom,shm-bridge-sm8150
>>>> +          - qcom,shm-bridge-sm8450
>>>> +      - const: qcom,shm-bridge
>>>> +
>>>
>>> Looks quite empty... Why this cannot be part of qcom,scm? IOW, why do
>>> you need new binding if you do not have any resources here and the block
>>> is essentially feature of qcom,scm firmware?
>> Since it's "discoverable" (via retval of an scm call), I'd second the
>> idea of probing this from within the SCM driver.
>>
>> Konrad
> 
> Downstream has a bunch of DT switches that we don't support for now
> upstream. I disagree about shoehorning this into the SCM driver. It
> really is a layer on top of SCM but also SCM is a user of this
> interface.

Sure, for the driver makes sense, but it does not really explain why DT
node is needed. It is not separate hardware. I doubt it is even separate
firmware, but part of SCM.

Best regards,
Krzysztof