Re: [PATCH v3 0/2] rng: Provide a RNG based on the RISC-V Zkr ISA extension

[Tom Rini <trini@konsulko.com>]

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On Wed, Nov 08, 2023 at 12:29:03AM +0000, Conor Dooley wrote:
> On Tue, Nov 07, 2023 at 06:23:05PM -0500, Tom Rini wrote:
[snip]
> > Thanks. Setting aside Simon's follow-up, this is what I was looking for.
> > We might have to wait for Heinrich to return from the conference to have
> > time to look at how to utilize the above and see what we can do from
> > there.
> 
> I did read that, but I don't think most of it is relevant to the binding
> itself. His five things were:
> | - U-Boot models hardware (and other things) as devices in driver model [1]
> 
> This I think should be satisfied. The Zkr CSR is a property of the CPU,
> and shouldn't have its own DT node IMO. Is it problematic for U-Boot to
> populate multiple devices for its driver model based on one DT node?
> I know in Linux that I can create devices using something like
> platform_device_register(), does U-Boot have a similar facility?
> https://elixir.bootlin.com/linux/latest/source/drivers/base/platform.c#L767
> 
> | - U-Boot requires devices to be in the devicetree, with very limited
> | exceptions [2]
> 
> | - Where multiple devices exist in a uclass, it is desirable to be able
> | to number them [3]
> 
> I'm not sure really how this one ties in. Do you need a number for each
> CPU that supports Zkr, since a system may be heterogeneous? I think that
> how you treat things like that is beyond communicating support via DT
> though, IMO the job of the DT is just to tell U-Boot on which CPUs it
> can access the seed CSR.
> 
> | - Similarly it is useful to be able select a particular device, e.g.
> | with a phandle [4]
> 
> I suppose a phandle to the CPU would work in this case.
> 
> | - U-Boot uses devicetree for configuration as it has no userspace

I mean, the reason I was setting aside Simon's question is that in my
mind, we (U-Boot) need to think about what we're declaring as a MUST
because the constant feedback that we get is "No, why does that need to
get added to DT? Can't you just use ... ?". So I do find your answers
above enlightening in that regard.

-- 
Tom

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