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

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Message-ID: <20231003102138.GB69443@aspen.lan>
Date:   Tue, 3 Oct 2023 11:21:38 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Flavio Suligoi <f.suligoi@...m.it>
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

On Tue, Oct 03, 2023 at 09:43:15AM +0000, Flavio Suligoi wrote:
> 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).

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).


Daniel.