Re: [PATCH v2 1/2] dt-bindings/display/bridge: sii902x: add optional power supplies

From: Laurent Pinchart
Date: Wed Apr 25 2018 - 18:04:58 EST

Hi Rob,

On Wednesday, 25 April 2018 20:11:23 EEST Rob Herring wrote:
> On Wed, Apr 25, 2018 at 04:17:25PM +0300, Laurent Pinchart wrote:
> > On Wednesday, 25 April 2018 15:20:04 EEST Philippe CORNU wrote:
> >> On 04/25/2018 11:01 AM, Laurent Pinchart wrote:
> >>> On Wednesday, 25 April 2018 10:53:13 EEST Philippe Cornu wrote:
> >>>> Add optional power supplies using the description found in
> >>>> "SiI9022A/SiI9024A HDMI Transmitter Data Sheet (August 2016)".
> >>>>
> >>>> There is a single 1v2 supply voltage named vcc12 from which cvcc12
> >>>> (digital core) and avcc12 (TMDS analog) are derived because according
> >>>> to this data sheet:
> >>>> "cvcc12 and avcc12 can be derived from the same power source"
> >>>
> >>> Shouldn't the power supplies be mandatory, as explained by Mark in
> >>>
> >>> ?
> >>
> >> Laurent,
> >> Many thanks Laurent for your comment, I understood the merge of the two
> >> 1v2 power supplies but missed the "mandatory" part... maybe because this
> >> patch (with optional power supplies) already got the reviewed-by from
> >> Rob, I thought the discussion thread you pointed out was applicable
> >> "only" to totally new driver documentation.
> >>
> >> So, on my side, as a "new user" of sii902x IC, no problem to put these
> >> power supplies as mandatory instead of optional properties but I would
> >> like to be sure this is applicable to both old and new bindings doc : )
> >
> > We obviously need to retain backward compatibility, so on the driver side
> > you need to treat those power supplies as optional. From a DT bindings
> > point of view, however, I think they should be mandatory for new DT.
> We don't really have a way to describe these 3 conditions (required for
> all, optional for all, and required for new). So generally we make
> additions optional. The exception sometimes is if we update all the dts
> files.

Can't we just make it mandatory in the bindings, as long as we treat it as
optional in drivers ?

> >> Rob,
> >> could you please confirm these power supply properties should be
> >> "mandatory"? if yes, should we then modify other optional properties like
> >> the reset-gpios too in the future?
> >
> > The GPIOs properties are different in my opinion, as there's no
> > requirement to connect for instance the reset pin to a GPIO controllable
> > by the SoC. The pin could be hardwired to VCC, or connected to a system
> > reset that is automatically managed without SoC intervention. The power
> > supplies, however, are mandatory, in the sense that the chip will not work
> > if you leave the power supplies unconnected.
> DT only needs to describe what matters to s/w. If a regulator is
> fixed and you don't need to know its voltage (or other read-only
> parameters), then there's not much point in putting it in DT.
> I'd probably base this more at a platform level and you either use
> regulator binding or you don't. It's perfectly valid that you want to do
> things like regulator setup, pin ctrl and muxing setup, etc. all in
> firmware and the OS doesn't touch any of that.
> That's all a big can of worms which we shouldn't solve on this 2 line
> change. I think this change is fine as-is, so:
> Reviewed-by: Rob Herring <robh@xxxxxxxxxx>


Laurent Pinchart