Re: [PATCH v3 1/2] dt-bindings: drm/bridge: adv7511: Add regulator bindings

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Tue 29 Nov 01:11 PST 2016, Laurent Pinchart wrote:

> Hi Archit,
> 
> (CC'ing Mark Brown)
> 
> On Tuesday 29 Nov 2016 13:41:33 Archit Taneja wrote:
> > On 11/29/2016 12:03 PM, Laurent Pinchart wrote:
> > > On Tuesday 29 Nov 2016 11:37:41 Archit Taneja wrote:
> > >> Add the regulator supply properties needed by ADV7511 and ADV7533.
> > >> 
> > >> The regulators are specified as optional properties since there can
> > >> be boards which have a fixed supply directly routed to the pins, and
> > >> these may not be modelled as regulator supplies.
> > > 
> > > That's why we have support for dummy supplies in the kernel, isn't it ?
> > > Isn't it better to make the supplies mandatory in the bindings (and
> > > obviously handling them as optional in the driver for
> > > backward-compatibility) ?
> >
> > I'm a bit unclear on this.
> > 
> > I thought we couldn't add mandatory properties once the device is already
> > present in DT for one or more platforms.
> 
> You can, as long as you treat them as optional in the driver to retain 
> backward compatibility. The DT bindings should document the properties 
> expected from a new platform (older versions of the bindings will always be 
> available in the git history).

If you document them as required and don't do anything special in the
implementation (i.e. just call devm_regulator_get() as usual) it will
just work, in the absence of the property you will get a dummy regulator
from the framework.

And then add the fixed-voltage regulators to the new DT to make that
properly describe the hardware.

> 
> > Say, if we do make it mandatory for future additions, we would need to have
> > DT property for the supplies for the new platforms. If the regulators on
> > these boards are fixed supplies, they would be need to be modeled
> > using "regulator-fixed", possibly without any input supply. Is that
> > what you're suggesting?
> 
> That's the idea, yes. Clock maintainers have a similar opinion regarding the 
> clock bindings, where a clock that is not optional at the hardware level 
> should be specified in DT even if it's always present.
> 

Further more, a DT binding for a particular block should describe that
block; so if we have three different 1.8V pins then the DT binding
should reflect this - even if our current platform have them wired to
the same regulator.

(And the supply names would preferably be based on the pin names in the
component data sheet)

Regards,
Bjorn