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

On Wed, Jul 21, 2021 at 12:18:03AM +0100, Andre Przywara wrote:

On Wed, 21 Jul 2021 08:02:42 +1000
Benjamin Herrenschmidt [off-list ref] wrote:

quoted

On Tue, 2021-07-20 at 17:16 +0100, Andre Przywara wrote:

quoted

quoted

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?  

quoted

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?

It's also worth pointing out that we're already doing the enumeration
part, making things a bus would just be about reorganising the code that
checks if services are present to a central place so it looks more Linux
style.  If anything I'd guess that if we get to the point where things
are slow enough to worry about having that code in one central place
would make doing something about it easier (eg, adding a "list all
services" service or firmware binding).