Re: [PATCH 1/2] dt-bindings: phy: imx8mq-usb: add phy tuning properties

[Johannes Zink]

Hi Rob,

On 4/12/23 15:39, Rob Herring wrote:
> On Tue, Apr 11, 2023 at 04:22:37PM +0200, Johannes Zink wrote:
> > Hi Krzystof,
> >
> > thank you for your explanations. As I'm still quite new to writing
> > bindings, I still have some questions:
> >
> > On Fri, 2023-04-07 at 11:03 +0200, Krzysztof Kozlowski wrote:
> > > On 05/04/2023 14:14, Johannes Zink wrote:
> > > > Hi Krysztof,
> > > >
> > > > thanks for your review, please find my questions below.
> > > >
> > > > On Wed, 2023-04-05 at 13:51 +0200, Krzysztof Kozlowski wrote:
> > > > > [snip]
> > > > > >         A phandle to the regulator for USB VBUS.
> > > > > >   
> > > > > > +  fsl,phy-tx-vref-tune:
> > > > > > +    description:
> > > > > > +      HS DC Voltage level adjustment
> > > > >
> > > > > "Level" in what units?
> > > >
> > > > The datasheet just shows percent, ranging from -6 to +24%, in 2%
> > > > increments. What unit would you suggest?
> > >
> > > percent
> > > https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml
> >
> > I am still a bit confused how to use this properly. How can I restrict
> > the values to multiples of 2 in order to avoid illegal values?
> >
> > At the moment the only thing I could come up with is something like
> >
> > fsl,phy-tx-vref-tune-percent:
> >    description: |
> >      Adjusts the high-speed DC level voltage
> >    $ref: /schemas/types.yaml#/definitions/int32
>
> Note that with standard unit suffixes, you don't need a type.
>
> >    minimum: -6
> >    maximum: 24
> >    default: 0
> >
> > Does something like this work? I am not quite sure if I am on the right
> > track here, especially as this requires a signed int, of which I have
> > not seen many examples so far.
>
> We'd have to change the type for -percent to signed. That's possible,
> but for vendor specific properties there's not much advantage to use
> standard units instead of just using the register values directly.

I don't have any objections to that, this is pretty much what I sent in 
my v1 patch <20230405112118.1256151-2-j.zink@xxxxxxxxxxxxxx>, but 
Krzysztof requested to change the vendor specific properties to use 
property-units.

Would something along the lines of the st,trim-hs-current on 
Documentation/devicetree/bindings/phy/phy-stm32-usbphyc.yaml be 
acceptable (i.e. use an enum and annotate the meaning of the values in 
the description)?

I will, nevertheless, try to make the descriptions a bit more verbose in 
my v2 (wherever the datasheet gives me proper informations), as 
Krzysztof requested.

Best regards
Johannes

> Rob

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