linux-kernel - RE: [PATCH v3 1/2] dt-bindings: backlight: Add MPS MP3309C

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Message-ID: <DU2PR01MB8034F17A9C81FE198CCAC5B7F9CBA@DU2PR01MB8034.eurprd01.prod.exchangelabs.com>
Date:   Wed, 4 Oct 2023 15:18:24 +0000
From:   Flavio Suligoi <f.suligoi@...m.it>
To:     Daniel Thompson <daniel.thompson@...aro.org>
CC:     Lee Jones <lee@...nel.org>, Jingoo Han <jingoohan1@...il.com>,
        Helge Deller <deller@....de>, Pavel Machek <pavel@....cz>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh@...nel.org>
Subject: RE: [PATCH v3 1/2] dt-bindings: backlight: Add MPS MP3309C

Hi Daniel,
...
> ...
> > > > > +required:
> > > > > +  - compatible
> > > > > +  - reg
> > > > > +  - max-brightness
> > > >
> > > > Why is this mandatory?
> > > >
> > > > There's no point in setting max-brightness when running in I2C
> > > > mode
> > > > (max- brightness should default to 31 in that case).
> > > >
> > > >
> > > > > +  - default-brightness
> > > >
> > > > Again. I'm not clear why this needs to be mandatory.
> > > >
> > > >
> > >
> > > Ok, you are right, I'll remove max-brightness and default-brightness
> > > from required properties list. I think to change these properties,
> > > for the pwm dimming, into a clearer:
> > >
> > > - brightness-levels (uint32)
> > > - default-brightness-levels (uint32).
> > >
> > > For example:
> > >
> > >   brightness-levels:
> > >     description:
> > >       Number of brightness levels. The actual brightness
> > >       level (PWM duty cycle) will be interpolated from 0 to this value.
> > >       0 means a  0% duty cycle (darkest/off), while the
> > > brightness-levels
> > represents
> > >       a 100% duty cycle (brightest).
> > >     $ref: /schemas/types.yaml#/definitions/uint32
> > >
> > >   default-brightness-level:
> > >     description:
> > >       The default brightness level (from 0 to brightness-levels)
> > >     $ref: /schemas/types.yaml#/definitions/uint32
> > >
> > > Example:
> > > brightness-levels = <10>;
> > > default-brightness-level = <6>;
> > >
> > > What do you think about this solution?
> >
> > If you want to introduce a brightness-levels property then I would
> > expect it to be defined with the same meaning as pwm-backlight (it's
> > not relevant to the bindings but ideally it would be implemented by
> > refactoring and reusing the code from pwm_bl.c).
> 
> ok, I'll use the brightness-levels property as used in pwm-backlight
> 
> >
> > Same with default-brightness-level although I'm not sure why one
> > wouldn't just use default-brightness for new bindings (doesn't
> > default-brightness-level simply do exactly the same thing as default-
> brightness).
> 
> ok for default-brightness instead of default-brightness-level

Just a question: default-brightness-level is the index into the brightness-levels array.
But, if I use default-brightness instead of default-brightness-level,  
should I consider default-brightness also as an index into brightness-levels array?
Or, in this case, have the default-brightness to be equal to one of the values inside the
brightness-levels array?

> 
> >
> >
> > Daniel.
> 
> Thanks an best regards,
> Flavio

Thanks,

Flavio