Re: [PATCH v2 1/4] devicetree: bindings: Properly document micrel ks8851 SPI chips

[Stephen Boyd]

On 05/28/14 10:12, Mark Brown wrote:
> On Wed, May 28, 2014 at 05:16:46PM +0200, Uwe Kleine-König wrote:
>> On Tue, May 27, 2014 at 02:40:15PM -0700, Stephen Boyd wrote:
>>> On 05/24/14 05:48, Mark Brown wrote:
>>>> So, according to the datasheet I managed to find this device has a
>>>> supply VDD_IO (so normally written vdd-io-supply here), some other
>>>> supplies which are tied to VDD_IO (so can probably be omitted) and a
>>>> supply VDD_A3.3 none of which are optional.  There is an internal
>>>> regulator which can be used to drop a higher voltage VDD_IO down for
>>>> some of the supplies tied to it but that's essentially a noop from
>>>> software as far as I can tell.  None of these supplies are obviously
>>>> optional, though I've not read the datasheet in detail so I may have
>>>> missed something here.
>> There is a difference between the supply being optional for the hardware
>> to work and the need to specify it in the device tree, isn't it? My
>> expectation is that when it's not specified there is just nothing the
>> the software needs to care for. 
> If the supply must always be physically present the bindings should be
> specified as it being mandatory and the code written in that fashion; as
> an extension Linux will put a dummy in but this is attempting to handle
> incorrect DTs.  This means we have functional error handling in cases
> where there is something to worry about and simplifies the code using
> the regulator.

Ok, you're saying the opposite of Rob. Should it be required or optional
in the DT binding?

>
> regulator_get_optional() should *only* be used if the supply may be
> omitted from the physical design and should generally always be
> accompanied by code which does something substantially different such as
> using an internal regulator or changing the source for a reference
> voltage instead.
>
>

Ok. Dave M has already picked up all these patches so I'll send a patch
to replace regulator_get_optional() with regulator_get() and fix up the
error handling unless I hear otherwise.

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