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

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Date:   Tue, 24 Oct 2023 16:08:56 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Flavio Suligoi <f.suligoi@...m.it>
Cc:     Lee Jones <lee@...nel.org>,
        Daniel Thompson <daniel.thompson@...aro.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>
Subject: Re: [PATCH 1/1] dt-bindings: backlight: mp3309c: remove two required
 properties

On Tue, Oct 24, 2023 at 07:53:38AM +0000, Flavio Suligoi wrote:
> > 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?
> 
> This is not a problem, because the device driver has not yet been included in any kernel.
> My patch for the device driver is still being analyzed by the maintainers.
> Only this dt-binding yaml file is already included in the "for-backlight-next" branch
> of the "backlight" kernel repository.
> At the moment, this driver is used only in a i.MX8MM board produced in my company,
> under my full control. No other developer is using it now.

Right. This is exactly the sort of commentary that you need to provide
up front, to have us spent a bunch of time going back and forth to
figure out :(

> > > 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?
> 
> In the first version of the driver this property was a "required property",
> but nobody has used this driver before, so this should be not a problem.

> > 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.
> 
> As said before, no one may have ever used this device driver,
> so I would leave only this new version of the example.

Okay. Please improve the commit message explaining why it is okay to
make these changes & send a v2.
The alternative is that Lee drops the dt-binding patch & you submit a
revised version of the binding alongside the next iteration of the
driver.

Cheers,
Conor.

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