linux-kernel - Re: [RFC 1/2] dt-bindings: clk: versaclock5: Add load capacitance properties

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Date:   Fri, 8 Jan 2021 23:49:29 +0100
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Adam Ford <aford173@...il.com>, linux-clk@...r.kernel.org
Cc:     aford@...conembedded.com,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/2] dt-bindings: clk: versaclock5: Add load capacitance
 properties

Hi Adam,

On 06/01/21 18:38, Adam Ford wrote:
> There are two registers which can set the load capacitance for
> XTAL1 and XTAL2. These are optional registers when using an
> external crystal.  Update the bindings to support them.
> 
> Signed-off-by: Adam Ford <aford173@...il.com>
> ---
>  .../devicetree/bindings/clock/idt,versaclock5.yaml   | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/clock/idt,versaclock5.yaml b/Documentation/devicetree/bindings/clock/idt,versaclock5.yaml
> index 2ac1131fd922..e5e55ffb266e 100644
> --- a/Documentation/devicetree/bindings/clock/idt,versaclock5.yaml
> +++ b/Documentation/devicetree/bindings/clock/idt,versaclock5.yaml
> @@ -59,6 +59,18 @@ properties:
>      minItems: 1
>      maxItems: 2
>  
> +  idt,xtal1-load-femtofarads:

I wonder whether we should have a common, vendor independent property.
In mainline we have xtal-load-pf (ti,cdce925.txt bindings) which has no
vendor prefix. However I don't know how much common it is to need
different loads for x1 and x2. Any hardware engineer around?

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 9000
> +    maximum: 25000
> +    description: Optional loading capacitor for XTAL1

Nit: I think the common wording is "load capacitor", not "loading
capacitor".

-- 
Luca