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

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Date:   Wed, 13 Jan 2021 15:36:48 +0100
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Adam Ford <aford173@...il.com>, Rob Herring <robh@...nel.org>
Cc:     linux-clk <linux-clk@...r.kernel.org>,
        Adam Ford-BE <aford@...conembedded.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/2] dt-bindings: clk: versaclock5: Add load capacitance
 properties

Hi Adam,

On 13/01/21 13:31, Adam Ford wrote:
> On Tue, Jan 12, 2021 at 9:16 PM Rob Herring <robh@...nel.org> wrote:
>>
>> On Wed, Jan 06, 2021 at 11:38:59AM -0600, 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:
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>
>> Already has a type, so you can drop the $ref.
>>
>>> +    minimum: 9000
>>> +    maximum: 25000
> 
> Luca,
> 
> Do you want the range to the 9000 - 25000 per the datasheet, or should
> I use the max value based on the programmer guide?  Currently, my
> intent was to cap the value to 11111b, so anyone who writes 23000,
> 24000, or 25000 will all be the same value based on the feedback I got
> from Renesas.

DT should describe the HW, so I'd use the same range that can be set in
hardware, regardless of driver support. Thus it should be:

9000 - [9000 + 430 * 32] = 9000 - 22760

-- 
Luca