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Date:   Mon, 5 Jun 2023 12:01:35 +0200
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From:   Mike Looijmans <mike.looijmans@topic.nl>
Subject: Re: [PATCH v2 1/2] dt-bindings: clock: Add nvmem-clock
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To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
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CC:     Conor Dooley <conor+dt@kernel.org>,
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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=20
that the fixed-clock implementation returns "void" in its=20
of_fixed_clk_setup() init function. The nvmem provider returns=20
EPROBE_DEFER because it isn't ready at this early stage, and this error=20
will not be propagated up because of the "void" signature. Thus, it's=20
never retried and the clock just disappears.


> Best regards,
> Krzysztof
>

--=20
Mike Looijmans
System Expert

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