linux-kernel - Re: [PATCH v2 10/10] ARM: dts: stm32: add RNG node for STM32MP13x platforms

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Message-ID: <abd1db1b-7cdb-177b-7995-23f500597155@foss.st.com>
Date:   Wed, 13 Sep 2023 09:52:36 +0200
From:   Gatien CHEVALLIER <gatien.chevallier@...s.st.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Olivia Mackall <olivia@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>
CC:     Lionel Debieve <lionel.debieve@...s.st.com>,
        <linux-crypto@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/10] ARM: dts: stm32: add RNG node for STM32MP13x
 platforms



On 9/12/23 16:38, Krzysztof Kozlowski wrote:
> On 11/09/2023 14:02, Gatien Chevallier wrote:
>> The RNG on STM32MP13 offers upgrades like customization of its
>> configuration and the conditional reset.
>>
>> The hardware RNG should be managed in the secure world for but it
>> is supported on Linux. Therefore, is it not default enabled.
>>
>> Signed-off-by: Gatien Chevallier <gatien.chevallier@...s.st.com>
>> ---
>>   arch/arm/boot/dts/st/stm32mp131.dtsi | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/st/stm32mp131.dtsi b/arch/arm/boot/dts/st/stm32mp131.dtsi
>> index ac90fcbf0c09..39db82b782eb 100644
>> --- a/arch/arm/boot/dts/st/stm32mp131.dtsi
>> +++ b/arch/arm/boot/dts/st/stm32mp131.dtsi
>> @@ -1220,6 +1220,14 @@ mdma: dma-controller@...00000 {
>>   			dma-requests = <48>;
>>   		};
>>   
>> +		rng: rng@...04000 {
>> +			compatible = "st,stm32mp13-rng";
>> +			reg = <0x54004000 0x400>;
>> +			clocks = <&rcc RNG1_K>;
>> +			resets = <&rcc RNG1_R>;
>> +			status = "disabled";
> 
> Why? What other resources are missing?
> 
> Best regards,
> Krzysztof
> 

Hello Krzysztof,

Our default implementation is to handle the RNG in OP-TEE for
these platforms. Therefore, it goes through optee-rng driver.
The RNG services are exposed by a PTA (Pseudo Trusted Application)
in OP-TEE. In this case, there's no need to enable the RNG node
in the Linux Kernel.

Best regards,
Gatien