linux-kernel - Re: [PATCH v2] hwrng: Add Arm SMCCC TRNG based driver

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Date:   Wed, 21 Jul 2021 00:18:03 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>, Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>, Will Deacon <will@...nel.org>,
        Ali Saidi <alisaidi@...zon.com>,
        Jon Nettleton <jon@...id-run.com>
Subject: Re: [PATCH v2] hwrng: Add Arm SMCCC TRNG based driver

On Wed, 21 Jul 2021 08:02:42 +1000
Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:

Hi,

> On Tue, 2021-07-20 at 17:16 +0100, Andre Przywara wrote:
> > Yes, a similar idea was already brought up before. I think there is even
> > the potential for something like an artificial SMCCC "bus", where those
> > services presentable as devices could be auto-detected (by checking
> > known function IDs), the respective drivers would then probe
> > automatically?  
> 
> Sounds like a boot time killer...

How so? To be clear, at the moment there is basically just the TRNG
service we would probe for, maybe FF-A, then adding as we go. But in
any case it would be just a handful, and querying is very quick
(SMC/HVC, then just a switch/case on the other side, and ERET).
Is there any particular scenario you are concerned about? Quick
starting guests?

> can we instead describe them in DT and/or ACPI ?

I think part of the idea of SMCCC is that it does NOT need firmware
advertisement, but can instead be discovered, through a safe interface.

Cheers,
Andre