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 06:23:37AM -0800, Heinrich Schuchardt wrote:
> On 11/7/23 16:34, Tom Rini wrote:
> > 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?
> 
> Devices in U-Boot are bound on the basis of a compatible string. All RISC-V
> CPU nodes have a compatible string 'riscv' but that does not provide any
> information about the existence of the Zkr extension. That information is in
> the 'riscv,isa-extensions' property of the cpu nodes (see
> Documentation/devicetree/bindings/riscv/cpus.yaml).
> 
> > > I know in Linux that I can create devices using something like
> > > platform_device_register(), does U-Boot have a similar facility?
> 
> This is what the U_BOOT_DRVINFO() macro in my driver does and which Simon
> discourages.

My current thoughts are that in this case we could use U_BOOT_DRVINFO()
like today and then have riscv_zkr_probe() be what checks the
riscv,isa-extensions property for an appropriate match? This would mean
we don't need any new nodes/compatibles/etc, and possibly not need any
bootph- properties added either? I assume we don't need the RNG so early
as for that to be an issue.

-- 
Tom

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