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Message-ID: <3d752603-365d-3a33-e13e-ca241cee9a11@gmail.com>
Date:   Wed, 27 Jul 2022 15:03:49 +0200
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Subject: Re: [PATCH 4/4] dt-bindings: firmware: Add Qualcomm UEFI Secure
 Application client
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To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Sudeep Holla <sudeep.holla@arm.com>
Cc:     Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Steev Klimaszewski <steev@kali.org>,
        Shawn Guo <shawn.guo@linaro.org>,
        Cristian Marussi <cristian.marussi@arm.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-arm-msm@vger.kernel.org, linux-efi@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20220723224949.1089973-1-luzmaximilian@gmail.com>
 <20220723224949.1089973-5-luzmaximilian@gmail.com>
 <20220726143005.wt4be7yo7sbd3xut@bogus>
 <829c8fee-cae5-597d-933d-784b4b57bd73@gmail.com>
 <20220726154138.74avqs6iqlzqpzjk@bogus>
 <d1bc99bb-82ce-aa6e-7fad-e9309fa1c19b@gmail.com>
 <7284953b-52bb-37ac-fbe1-1fa845c44ff9@linaro.org>
From:   Maximilian Luz <luzmaximilian@gmail.com>
In-Reply-To: <7284953b-52bb-37ac-fbe1-1fa845c44ff9@linaro.org>
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On 7/27/22 13:38, Krzysztof Kozlowski wrote:
> On 26/07/2022 19:01, Maximilian Luz wrote:
>> On 7/26/22 17:41, Sudeep Holla wrote:
>>> On Tue, Jul 26, 2022 at 05:15:41PM +0200, Maximilian Luz wrote:
>>>>
>>>> So ultimately I think it's better to add a DT entry for it.
>>>
>>> I disagree for the reason that once you discover more apps running on the
>>> secure side, you want to add more entries and update DT on the platform
>>> every time you discover some new firmware entity and you wish to interact
>>> with it from the non-secure side.
>>
>> Just as you'll have to add a driver to the kernel and update whatever is
>> probing the TrEE interface and add those strings to that interface. If
>> you then start doing SoC-specific lists, I think you'd be pretty much
>> re-implementing a DT in the kernel driver...
> 
> But you don't have any of these names in the DT either. Your DT node
> only indicates the presence of your driver, but does not hold any
> additional information like these IDs.

Because the compatible implicates the ID-string which implicates the driver
interface. If the ID-string for uefisecapp would be different we'd very likely
need a different driver for that as well, meaning a new compatible too. I
thought it would be superfluous to put that in the DT.
  
> Basically we start modelling firmware components in devicetree. :/

Is there really a good way around it? As far as I can see the
alternative (especially for the apps that need to be loaded manually) is
hard-coding everything in the driver. Which IMHO just spreads device
specific information everywhere.

Also: Let's use the TPM app as example. If that would be a SPI or I2C
device, you'd model it in the DT. Just because it's a hardware device
that's accessible via SCM/firmware you now don't?

If I were absolutely certain that there is a reliable mechanism to
detect these apps, I'd agree with having a driver to instantiate those
devices. But I am not.

Regards,
Max