Re: [PATCH v2 1/2] dt-bindings: clock: Add nvmem-clock

[Mike Looijmans]

On 05-06-2023 12:13, Krzysztof Kozlowski wrote:
> On 05/06/2023 12:01, Mike Looijmans wrote:
> > On 31-05-2023 21:27, Krzysztof Kozlowski wrote:
> > > On 26/05/2023 16:38, Mike Looijmans wrote:
> > > > Add bindings for a fixed-rate clock that retrieves its rate from an
> > > > NVMEM provider. This allows to store clock settings in EEPROM or EFUSE
> > > > or similar device.
> > > >
> > > > Component shortages lead to boards being shipped with different clock
> > > > crystals, based on what was available at the time. The clock frequency
> > > > was written to EEPROM at production time. Systems can adapt to a wide
> > > > range of input frequencies using the clock framework, but this required
> > > > us to patch the devicetree at runtime or use some custom driver. This
> > > > provides a more generic solution.
> > > This does not look like real hardware. I mean, the clock does not fetch
> > > its rate from nvmem, right? It's the Linux which does it, so basically
> > > you described here driver, not hardware.
> > Right, this just reads a setting from an NVMEM provider.
> > > Extend existing fixed-clock bindings to allow reading frequency via
> > > nvmem cells.
> > I just tried and implemented this, but it does not work. The reason is
> > that the fixed-clock implementation returns "void" in its
> > of_fixed_clk_setup() init function. The nvmem provider returns
> > EPROBE_DEFER because it isn't ready at this early stage, and this error
> > will not be propagated up because of the "void" signature. Thus, it's
> > never retried and the clock just disappears.
> Linux driver problems are not a reason to add bindings for virtual
> hardware...
Okay, so what are you proposing?

The implementation needs a compatible string other than "fixed-clock", 
because of the way the fixed-clock driver is being loaded (it can never 
be deferred).

So I should add another compatible string to fixed-clock.yaml? That'd 
make the syntax in fixed-clock.yaml rather awkward, since some 
properties would only apply to some compatible strings?

--
Mike Looijmans
System Expert

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