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

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Message-ID: <20250409103303.dkrrvp7mdctx32pd@uda0497581-HP>
Date: Wed, 9 Apr 2025 16:03:03 +0530
From: Manorit Chawdhry <m-chawdhry@...com>
To: Michael Walle <mwalle@...nel.org>
CC: "Kumar, Udit" <u-kumar1@...com>, 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 Michael,

On 13:09-20250401, Michael Walle wrote:
> 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?

Wondering if this would be of interest to you [0]. I think since this
device only has one TRNG, there has to be a master around and we can
mitigate that from OP-TEE as of now, incase anything changes in future
then the communication channel between OP-TEE and the secure firmware
can be established but currently it's still at work. I think the best
way to go forward is to get the numbers from OP-TEE atm IMHO.

[0]: https://github.com/u-boot/u-boot/blob/master/drivers/rng/optee_rng.c

Regards,
Manorit

> 
> -michael