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

Mathieu Dubois-Briand
2025-03-25T15:56:23Z

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