Re: [PATCH V4 3/8] backlight: qcom-wled: Add new properties for PMI8998

Bjorn Andersson
2018-09-03T18:55:10Z

On Wed 15 Aug 22:23 PDT 2018, kgunda@codeaurora.org wrote:

> On 2018-08-07 10:53, Bjorn Andersson wrote:
> > On Mon 09 Jul 03:22 PDT 2018, Kiran Gunda wrote:
> > > diff --git
> > > a/Documentation/devicetree/bindings/leds/backlight/qcom-wled.txt
> > > b/Documentation/devicetree/bindings/leds/backlight/qcom-wled.txt
> > [..]
> > > - qcom,num-strings
> > > Usage: optional
> > > Value type: <u32>
> > > Definition: #; number of led strings attached;
> > > - value from 1 to 3. default: 2
> > > - This property is supported only for PM8941.
> > > + value: For PM8941 from 1 to 3.
> > > + For PMI8998 from 1 to 4.
> > [..]
> > > +- qcom,enabled-strings
> > > + Usage: optional
> > > + Value tyoe: <u32 array>
> > > + Definition: Array of the WLED strings numbered from 0 to 3. Each
> > > + string of leds are operated individually. Specify the
> > > + list of strings used by the device. Any combination of
> > > + led strings can be used.
> > [..]
> > >
> > > Example:
> > >
> > > @@ -99,4 +146,5 @@ pm8941-wled@d800 {
> > > qcom,switching-freq = <1600>;
> > > qcom,ovp = <29>;
> > > qcom,num-strings = <2>;
> > > + qcom,enabled-strings = <0x00 0x01>;
> >
> > Nit. I would assume that specifying qcom,num-strings = <2> implies that
> > the first 2 strings are used, so one would not also specify
> > qcom,enabled-strings.
> >
> Thanks Bjorn for reviewing the series !
>
> "qcom,enabled-strings" need be specified along with the "qcom,num-strings".
> Because the enabled-strings can be <0, 2> or <0, 3 > also. The driver picks
> the string
> configuration from the enabled-strings array and enable only those
> current-sinks.
>

The original binding described qcom,num-strings to mean "the first N
strings", requiring qcom,enabled-strings now would break backwards
compatibility with this binding.

In the case that qcom,enabled-strings is specified we can easily derive
num-strings from the listed entires. So I would suggest that you look
for enabled-strings and if not found fall back to checking for
num-strings.

Regards,
Bjorn