Re: [PATCH 2/3] ieee802154: Add device tree documentation for CA8210

[Stefan Schmidt <stefan@osg.samsung.com>]

Hello.

On 27/10/16 00:33, Stefan Schmidt wrote:
> Hello.
>
> On 25/10/16 18:36, Harry Morris wrote:
>> Hi Stefan,
>>
>> On 25/10/2016 16:54, Stefan Schmidt wrote:
>>> Start should with a capital S here as you do on all other lines. Total
>>> nitpick. :)
>> Perfect, I'm sure there's a few more elsewhere I've missed
>>>> +    - reg:                  Controlling chip select
>>>> +    - spi-max-frequency:    Maximum clock speed, should be *less than*
>>>> +                            4000000
>>>> +    - spi-cpol:             Invert clock polarity
>>>
>>> Is this a mandatory field for the bindings? I would expect one being
>>> the default and used while the other one being an optional property
>>> and only used when the hardware setup needs this. Does this make sense?
>> I'm afraid not, my understanding is that the spi-cpol property is used
>> by the spi master driver rather than the device driver, so if I need
>> CPOL=1 (which the CA8210 always does) then the user doesn't have a
>> choice but to specify spi-cpol here? As omitting would cause the spi
>> master to use CPOL=0 for the attached slave.
>
> I would expect there is a way to set this in the driver itself as it is
> the default and the only working mode. Having to set it in the device
> tree bindings seems odd as this is really no option or parameter that
> can be changed.
>
> Did you look around in other SPI driver so see how they handle such a
> situation?

I did look around myself quickly and it seems indeed the way to set the 
clock polarity. Just keep it. Maybe adjust the description to "Requires 
invert clock polarity".

regards
Stefan Schmidt