[U-Boot] ns16550: change reg-shift property default to zero

[Thomas Chou <thomas@wytron.com.tw>]

Hi Stephen,

On 2015?12?08? 01:32, Stephen Warren wrote:
> On 12/06/2015 03:07 PM, Tom Rini wrote:
>> On Sun, Nov 29, 2015 at 02:01:03PM +0800, Thomas Chou wrote:
>>
>>> Change reg-shift property default to zero. When the integer property
>>> is missing, it should be taken as zero. This is consistent to Linux
>>> drivers/tty/serial/of_serial.c.
>
> It's not generally true that missing properties have value zero. Rather,
> whatever values was assumed by the semantics of the binding before that
> optional property was defined should be assumed.
>
> What the Linux kernel driver does also isn't justification for this
> change, since DT bindings define how they work, rather than a particular
> OS implementation forcing the hand of the binding.
>
> The DT binding documentation must state the default value/semantics for
> any optional property. Can you please make sure the DT binding
> documentation is updated to describe this case?
>
> (Note that I have no objection to this patch; the actual change seems
> fine. It's simply that the justifications given in the patch description
> for it aren't entirely robust.)
>

Thanks. Will send a follow-up patch for the DT binding.

Best regards,
Thomas