Re: [PATCH 1/1] dt-bindings: backlight: mp3309c: remove two required properties

[Conor Dooley <conor@kernel.org>]

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On Mon, Oct 23, 2023 at 09:28:03AM +0000, Flavio Suligoi wrote:
> > On Fri, Oct 20, 2023 at 03:54:33PM +0200, Flavio Suligoi wrote:
> > > The two properties:
> > >
> > > - max-brightness
> > > - default brightness
> > >
> > > are not really required, so they can be removed from the "required"
> > > section.
> > 
> > Why are they not required? You need to provide an explanation.
> 
> The "max-brightness" is not more used now in the driver (I used it in the first version
> of the driver).

If it is not used any more, what happens when someone passes an old
devicetree to the kernel, that contains max-brightness, but not any of
your new properties?

> The "default-brightness", if omitted in the DT, is managed by the device driver,
> using a default value. This depends on the dimming mode used:

For default-brightness, has here always been support in the driver for
the property being omitted, or is this newly added?

> - for the "analog mode", via I2C commands, this value is fixed by hardware (=31)
> - while in case of pwm mode the default used is the last value of the 
>   brightness-levels array.
> 
> Also the brightness-levels array is not required; if it is omitted, the driver uses 
> a default array of 0..255 and the "default-brightness" is the last one, which is "255".

Firstly, this is the sort of rationale that needs to be put into your
commit messages, rather than bullet pointed lists of what you have done.

Secondly, what about other operating systems etc, do any of those support
this platform and depend on presence of these properties?

> 
> > > Other changes:
> > >
> > > - improve the backlight working mode description, in the "description"
> > >   section
> > 
> > > - update the example, removing the "max-brightness" and introducing the
> > >   "brightess-levels" property
> > 
> > Why is this more useful?
> 
> I introduced the "brightness-levels" instead of "max-brightness" for homogeneity,
> since the "analog mode" dimming has a brightness-levels array fixed by hardware (0..31).
> In this way also the "pwm" mode can use the same concepts of array of levels.

What I would like is an explanation in the commit message as to why the
revised example is more helpful than the existing (and
must-remain-valid) one.

Cheers,
Conor.

> > 
> > >
> > > Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
> > > ---
> > >  .../bindings/leds/backlight/mps,mp3309c.yaml           | 10 ++++------
> > >  1 file changed, 4 insertions(+), 6 deletions(-)
> > >
> > > diff --git
> > a/Documentation/devicetree/bindings/leds/backlight/mps,mp3309c.yaml
> > b/Documentation/devicetree/bindings/leds/backlight/mps,mp3309c.yaml
> > > index 4191e33626f5..527a37368ed7 100644
> > > ---
> > a/Documentation/devicetree/bindings/leds/backlight/mps,mp3309c.yaml
> > > +++
> > b/Documentation/devicetree/bindings/leds/backlight/mps,mp3309c.yaml
> > > @@ -14,8 +14,8 @@ description: |
> > >    programmable switching frequency to optimize efficiency.
> > >    It supports two different dimming modes:
> > >
> > > -  - analog mode, via I2C commands (default)
> > > -  - PWM controlled mode.
> > > +  - analog mode, via I2C commands, as default mode (32 dimming levels)
> > > +  - PWM controlled mode (optional)
> > >
> > >    The datasheet is available at:
> > >    https://www.monolithicpower.com/en/mp3309c.html
> > > @@ -50,8 +50,6 @@ properties:
> > >  required:
> > >    - compatible
> > >    - reg
> > > -  - max-brightness
> > > -  - default-brightness
> > >
> > >  unevaluatedProperties: false
> > >
> > > @@ -66,8 +64,8 @@ examples:
> > >              compatible = "mps,mp3309c";
> > >              reg = <0x17>;
> > >              pwms = <&pwm1 0 3333333 0>; /* 300 Hz --> (1/f) * 1*10^9 */
> > > -            max-brightness = <100>;
> > > -            default-brightness = <80>;
> > > +            brightness-levels = <0 4 8 16 32 64 128 255>;
> > > +            default-brightness = <6>;
> > >              mps,overvoltage-protection-microvolt = <24000000>;
> > >          };
> > >      };
> > > --
> > > 2.34.1
> > >

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