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

From: Andre Przywara
Date: Tue Jul 20 2021 - 19:20:16 EST

On Wed, 21 Jul 2021 08:02:42 +1000
Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> wrote:


> 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.