Re: [PATCH 3/3] iio: imu: bmi160: Remove potential undefined behavior in bmi160_config_pin()

["Nuno Sá" <noname.nuno@gmail.com>]

On Mon, 2026-03-09 at 09:03 -0700, Josh Poimboeuf wrote:
> If 'pin' is not one of its expected values, the value of
> 'int_out_ctrl_shift' is undefined.  With UBSAN enabled, this causes
> Clang to generate undefined behavior, resulting in the following
> warning:
> 
>   drivers/iio/imu/bmi160/bmi160_core.o: warning: objtool: bmi160_setup_irq() falls through to next
> function __cfi_bmi160_core_runtime_resume()
> 
> Prevent the UB and improve error handling by adding a BUG() if 'pin' has
> an unexpected value.
> 
> Cc: Jonathan Cameron <jic23@kernel.org>
> Cc: David Lechner <dlechner@baylibre.com>
> CC: Nuno Sá <nuno.sa@analog.com>
> Cc: Andy Shevchenko <andy@kernel.org>
> Fixes: 895bf81e6bbf ("iio:bmi160: add drdy interrupt support")
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Closes: https://lore.kernel.org/a426d669-58bb-4be1-9eaa-6f3d83109e2d@app.fastmail.com
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
>  drivers/iio/imu/bmi160/bmi160_core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iio/imu/bmi160/bmi160_core.c b/drivers/iio/imu/bmi160/bmi160_core.c
> index 5f47708b4c5d..e5326df75e49 100644
> --- a/drivers/iio/imu/bmi160/bmi160_core.c
> +++ b/drivers/iio/imu/bmi160/bmi160_core.c
> @@ -579,6 +579,8 @@ static int bmi160_config_pin(struct regmap *regmap, enum bmi160_int_pin pin,
>  		int_latch_mask = BMI160_INT2_LATCH_MASK;
>  		int_map_mask = BMI160_INT2_MAP_DRDY_EN;
>  		break;
> +	default:
> +		BUG();
>  	}
>  	int_out_ctrl_mask = BMI160_INT_OUT_CTRL_MASK << int_out_ctrl_shift;
>  

AFAIK, BUG() is not something we should use lightly so I wonder why having it rather that a normal
'return -EINVAL'?

At the very least, it could be WARN but I still think that's too much for a device .probe(). Any
special reason using BUG()?

Also seems like:

https://elixir.bootlin.com/linux/v7.0-rc2/source/drivers/iio/imu/bmi160/bmi160_core.c#L624

could be improved? Like setting 'pin_name' in the first switch() case.

- Nuno Sá