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

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Message-ID: <Z-LVrdvKCBI5x2wy@smile.fi.intel.com>
Date: Tue, 25 Mar 2025 18:11:25 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Mathieu Dubois-Briand <mathieu.dubois-briand@...tlin.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 Tue, Mar 25, 2025 at 04:56:20PM +0100, Mathieu Dubois-Briand wrote:
> 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:

...

> > > +	int val;

Btw, this has to be unsigned to match the API.

> > > +	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;
> > > +	}

> > > +	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).

With the above fix it makes sense, but it's not clear for the reader still.
What you want is most likely to call sign_extend32().

-- 
With Best Regards,
Andy Shevchenko