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

On Wed, May 28, 2014 at 10:16 AM, Uwe Kleine-König
[off-list ref] wrote:

Hello Stephen,

On Tue, May 27, 2014 at 02:40:15PM -0700, Stephen Boyd wrote:

quoted

On 05/24/14 05:48, Mark Brown wrote:

quoted

On Fri, May 23, 2014 at 12:57:17PM -0700, Stephen Boyd wrote:

quoted

 Optional properties:
-- vdd-supply:     supply for Ethernet mac
+- vdd-supply: analog 3.3V supply for Ethernet mac
+- vdd-io-supply: digital 1.8V IO supply for Ethernet mac

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.

Yes, agreed.

Of course you could have cases where a supply at the h/w level is
optional like if a supply can be powered externally or via an internal
regulator. Those cases will have to be made clear in the binding, but
a heading "Optional properties" in a binding doc means properties
which are optional to specify in DT.

Rob