linux-kernel - Re: [PATCH v5 2/4] backlight: add max25014atg backlight

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Message-ID: <aRG359gIeP48V2ZZ@aspen.lan>
Date: Mon, 10 Nov 2025 10:01:11 +0000
From: Daniel Thompson <daniel@...cstar.com>
To: Maud Spierings <maudspierings@...ontroll.com>
Cc: Lee Jones <lee@...nel.org>, Daniel Thompson <danielt@...nel.org>,
	Jingoo Han <jingoohan1@...il.com>, Pavel Machek <pavel@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Helge Deller <deller@....de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, dri-devel@...ts.freedesktop.org,
	linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 2/4] backlight: add max25014atg backlight

On Mon, Nov 10, 2025 at 09:40:07AM +0100, Maud Spierings wrote:
> On 11/7/25 17:14, Daniel Thompson wrote:
> > On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
> > > +/**
> > > + * @brief control the brightness with i2c registers
> > > + *
> > > + * @param regmap trivial
> > > + * @param brt brightness
> > > + * @return int
> > > + */
> > > +static int max25014_register_control(struct regmap *regmap, uint32_t brt)
> >
> > This isn't a good name for a function. It doesn't really say what it
> > does. Please find a more descriptive name.
>
> Having a lot of difficulties find a succinct name that fits better,
> max25014_register_brightness_control()?
> max25014_i2c_brightness_control()?

I'd focus on what it does rather than how it does it meaning something
like max25014_update_brightness() would work.

However, at present, this code is only called from
max25014_update_status() so the simplest thing to do is to move the
code into max25014_update_status() and remove this function entirely
(then it doesn't matter what it is called ;-) ).


> > > +/*
> > > + * 1. disable unused strings
> > > + * 2. set dim mode
> > > + * 3. set initial brightness
> >
> > How does this code set the initial brightness? It doens't set the
> > MAX25014_TON* registers.
>
> Yep forgot to remove that, I discovered the backlight core takes care of the
> default brightness, so I removed it from here.

What do you mean by this? Are you sure you aren't relying on another
driver to enable the backlight rather than the backlight core?

> > > + * 4. set setting register
> > > + * 5. enable the backlight
> > > + */
> > > +static int max25014_configure(struct max25014 *maxim)


> > > +static int max25014_probe(struct i2c_client *cl)
> > > <snip>
> > > +
> > > +	/* Enable can be tied to vin rail wait if either is available */
> > > +	if (maxim->enable || maxim->vin) {
> > > +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
> > > +		usleep_range(2000, 2500);
> > > +	}
> >
> > If you really want to keep the devm_regulator_get_optional() I guess
> > maybe you could persuade me it's need to avoid this sleep... although
> > I'd be fairly happy to remove the NULL checks here too!
>
> Just wait unconditionally?

If you think it will be unusual for the driver to be used without enable
or regulator then it's ok to wait unconditionally (all examples you
have added so far have an enable pin).


Daniel.