linux-kernel - Re: [PATCH] arm64: dts: ti: k3-am62p-j722s: add rng node

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Message-ID: <ea82dc29e93d53b659916f2fed10982b@kernel.org>
Date: Tue, 01 Apr 2025 13:09:30 +0200
From: Michael Walle <mwalle@...nel.org>
To: "Kumar, Udit" <u-kumar1@...com>
Cc: Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>, Tero
 Kristo <kristo@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: ti: k3-am62p-j722s: add rng node

Hi Udit,

>>>>>> --- a/arch/arm64/boot/dts/ti/k3-am62p-j722s-common-main.dtsi
>>>>>> [..]
>>>>> For completeness , this is ok to add this node but should be kept 
>>>>> disabled
>>>> Shouldn't it be "reserved" then, see [1].
>>> yes, should be reserved.
>>> 
>>> With marking status as reserved.
>>> 
>>> Please use Reviewed-by: Udit Kumar <u-kumar1@...com>
>> Thanks.
>> 
>>>>> similar to
>>>>> 
>>>>> https://github.com/torvalds/linux/blob/master/arch/arm64/boot/dts/ti/k3-j7200-mcu-wakeup.dtsi#L662
>>>> j784s4, j721e and j721s2 have them enabled. What is the rule here?
>>> J784s4, j721e and j721s2 SOCs has two TRNG blocks,
>>> 
>>> example for j721e, one is used by kernel [0] and another by optee 
>>> [1].
>>> 
>>> 
>>>> You also disable the hwrng in optee in your evm according to [2]:
>>>> CFG_WITH_SOFTWARE_PRNG=y
>>> We are planning to use this hardware block by secure firmware.
>>> 
>>> Therefore request not to use by optee as well
>> How will you be able to access the RNG from linux and u-boot? I'm
>> asking because I'll need it in u-boot for the lwip stack and the
>> HTTPS protocol.
> 
> For now,  If you need TRNG then I can suggest to use optee TRNG (ie 
> build
> optee with HW TRNG).

I'll be using an uboot TRNG driver. But how will that work in
the future if the RNG is used by the secure firmware?

-michael