Re: [PATCH v4 1/2] dt-bindings: clock: fixed-clock: Add nvmem support

[Mike Looijmans]

On 08-06-2023 00:41, Rob Herring wrote:
> On Mon, Jun 05, 2023 at 04:01:48PM +0200, 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.
> >
> > Signed-off-by: Mike Looijmans <mike.looijmans@xxxxxxxx>
> >
> > ---
> >
> > Changes in v4:
> > Use proper "if" block and add example dts
> >
> > Changes in v3:
> > Modify fixed-clock instead of introducing nvmem-clock
> >
> > Changes in v2:
> > Changed "fixed-clock" into "nvmem-clock" in dts example
> > Add minItems:1 to nvmem-cell-names
> >
> >   .../bindings/clock/fixed-clock.yaml           | 42 ++++++++++++++++++-
> >   1 file changed, 41 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/devicetree/bindings/clock/fixed-clock.yaml b/Documentation/devicetree/bindings/clock/fixed-clock.yaml
> > index b0a4fb8256e2..71a5791da438 100644
> > --- a/Documentation/devicetree/bindings/clock/fixed-clock.yaml
> > +++ b/Documentation/devicetree/bindings/clock/fixed-clock.yaml
> > @@ -12,7 +12,9 @@ maintainers:
> >   
> >   properties:
> >     compatible:
> > -    const: fixed-clock
> > +    enum:
> > +      - fixed-clock
> > +      - fixed-clock-nvmem
> >   
> >     "#clock-cells":
> >       const: 0
> > @@ -26,11 +28,41 @@ properties:
> >     clock-output-names:
> >       maxItems: 1
> >   
> > +  nvmem-cells:
> > +    minItems: 1
> > +    maxItems: 2
> > +    description:
> > +      Reads clock-frequency and/or clock-accuracy from an NVMEM provider in
> > +      binary native integer format. The size of the NVMEM cell can be 1, 2, 4
> > +      or 8 bytes. If the contents of the nvmem are all zeroes or all 0xff, the
> > +      value reverts to the one given in the property.
> > +
> > +  nvmem-cell-names:
> > +    minItems: 1
> > +    items:
> > +      - const: clock-frequency
> > +      - const: clock-accuracy
> > +
> >   required:
> >     - compatible
> >     - "#clock-cells"
> >     - clock-frequency
> >   
> > +allOf:
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            const: fixed-clock-nvmem
> > +    then:
> > +      required:
> > +        - nvmem-cells
> > +        - nvmem-cell-names
> > +    else:
> > +      properties:
> > +        nvmem-cells: false
> > +        nvmem-cell-names: false
> > +
> >   additionalProperties: false
> >   
> >   examples:
> > @@ -41,4 +73,12 @@ examples:
> >         clock-frequency = <1000000000>;
> >         clock-accuracy = <100>;
> >       };
> > +  - |
> > +    clock {
> > +      compatible = "fixed-clock-nvmem";
> > +      #clock-cells = <0>;
> > +      clock-frequency = <48000000>;
>
> If the freq comes from nvmem, why is this needed?

Not needed, but it's a nice default in case the NVMEM is still 'blank'. With a 
separate schema (see next comment), something like "clock-frequency-default" 
would be more appropriate.

> I think this should probably be a separate schema file as the only
> other thing shared is #clock-cells.

Yep, I implemented it this way as suggested by Krysztof.

I don't care much either way, I'll send a v5 with a separate yaml file, if 
Krysztof agrees.


--
Mike Looijmans
System Expert

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