linux-kernel - Re: [PATCH v5 10/11] input: misc: Add support for MAX7360 rotary

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Message-Id: <D8PGXIKGXXK9.244NSFST6C0YD@bootlin.com>
Date: Tue, 25 Mar 2025 16:56:20 +0100
From: "Mathieu Dubois-Briand" <mathieu.dubois-briand@...tlin.com>
To: "Andy Shevchenko" <andriy.shevchenko@...el.com>
Cc: "Lee Jones" <lee@...nel.org>, "Rob Herring" <robh@...nel.org>,
 "Krzysztof Kozlowski" <krzk+dt@...nel.org>, "Conor Dooley"
 <conor+dt@...nel.org>, "Kamel Bouhara" <kamel.bouhara@...tlin.com>, "Linus
 Walleij" <linus.walleij@...aro.org>, "Bartosz Golaszewski" <brgl@...ev.pl>,
 "Dmitry Torokhov" <dmitry.torokhov@...il.com>,
 Uwe Kleine-König <ukleinek@...nel.org>, "Michael Walle"
 <mwalle@...nel.org>, "Mark Brown" <broonie@...nel.org>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, "Danilo Krummrich" <dakr@...nel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-gpio@...r.kernel.org>, <linux-input@...r.kernel.org>,
 <linux-pwm@...r.kernel.org>, Grégory Clement
 <gregory.clement@...tlin.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v5 10/11] input: misc: Add support for MAX7360 rotary

On Wed Mar 19, 2025 at 1:11 PM CET, Andy Shevchenko wrote:
> On Tue, Mar 18, 2025 at 05:26:26PM +0100, Mathieu Dubois-Briand wrote:
> > Add driver for Maxim Integrated MAX7360 rotary encoder controller,
> > supporting a single rotary switch.
>
> ...
>
> > +static irqreturn_t max7360_rotary_irq(int irq, void *data)
> > +{
> > +	struct max7360_rotary *max7360_rotary = data;
> > +	int val;
> > +	int ret;
> > +
> > +	ret = regmap_read(max7360_rotary->regmap, MAX7360_REG_RTR_CNT, &val);
> > +	if (ret < 0) {
> > +		dev_err(&max7360_rotary->input->dev,
> > +			"Failed to read rotary counter\n");
> > +		return IRQ_NONE;
> > +	}
> > +
> > +	if (val == 0) {
> > +		dev_dbg(&max7360_rotary->input->dev,
> > +			"Got a spurious interrupt\n");
> > +
> > +		return IRQ_NONE;
> > +	}
> > +
> > +	input_report_rel(max7360_rotary->input, max7360_rotary->axis,
> > +			 (int8_t)val);
>
> This is strange:
> 1) why casting to begin with?
> 2) why to C type and not kernel (s8) type?
>

I believe the cast is needed, as, while the value read with
regmap_read() is stored in an int, the underlying value is indeed a
signed 8 bits integer.

Without cast negative values will not be correct: -1 (0xFF) -> will be
interpreted as 255 (0x000000FF).

Ok for s8.

Thanks for your review
Mathieu

-- 
Mathieu Dubois-Briand, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com