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

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Date:   Thu, 28 Jul 2022 16:09:44 +0200
From:   Maximilian Luz <luzmaximilian@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Steev Klimaszewski <steev@...i.org>,
        Shawn Guo <shawn.guo@...aro.org>,
        Cristian Marussi <cristian.marussi@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org, linux-efi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] dt-bindings: firmware: Add Qualcomm UEFI Secure
 Application client

On 7/28/22 15:42, Sudeep Holla wrote:
> On Thu, Jul 28, 2022 at 01:45:57PM +0200, Maximilian Luz wrote:
>>
>> Would something like this work for you: Add a compatible for the TrEE
>> interface (e.g. qcom,sc8180x-tee) but not for the specific apps running
> 
> IIUC, you would introduce a compatible for each unique production if there
> is a need. This constitutes as a strong need for that, but you need just
> that, no need to have any notion or info to indicate TrEE/TEE as you know
> this product runs those in TEE.
> 
> In short, just use the platform specific(not SoC or SoC family) specific
> compatible to initialise your driver and don't introduce any specific
> compatible for this particular firmware interface need.

As Krzysztof mentioned, it would be good to ensure proper device
ordering wrt. SCM. Having a device node for the overall TrEE interface
would allow specifying that via DT. We could then still use the platform
compatible to load the specific things inside that driver.
Alternatively, we would need to do this extra stuff in qcom_scm.

I think separating this from qcom_scm into a new driver would be better
from a code separation and maintenance point of view. Also, this
reflects what's present in ACPI: There is a QCOM040B device for SCM and
a QCOM0476 device for TrEE.

Regards,
Max