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

["Michael Walle" <mwalle@kernel.org>]

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Hi Manorit,

> > > > > > > > --- 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@ti.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.

I saw the optee rng. But as of now, the instructions are to use a
software PRNG for optee. Thus, if someone compiles optee by
following the instructions, it's unlikely to work.

Would TI willing to agree to change the building docs and enable the
TRNG in optee and then work on moving the TRNG into the secure
firmware and build a channel between optee and that firmware? Right
now, the TRNG seems pretty useless as we cannot use it neither from
u-boot or linux (and being future proof).

-michael

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