linux-kernel - Re: [PATCH] iio: adc: ti_am335x_adc: Limit step

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Message-ID: <20251012201647.7e7869ad@jic23-huawei>
Date: Sun, 12 Oct 2025 20:16:47 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Pei Xiao <xiaopei01@...inos.cn>
Cc: dlechner@...libre.com, nuno.sa@...log.com, andy@...nel.org,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, kernel test robot
 <lkp@...el.com>
Subject: Re: [PATCH] iio: adc: ti_am335x_adc: Limit step_avg to valid range
 for gcc complains

On Sat, 11 Oct 2025 15:10:51 +0800
Pei Xiao <xiaopei01@...inos.cn> wrote:

> FIELD_PREP() checks that a value fits into the available bitfield, add a
> check for step_avg to fix gcc complains.
> 
> which gcc complains about:
>   drivers/iio/adc/ti_am335x_adc.c: In function 'tiadc_step_config':
>   include/linux/compiler_types.h:572:38: error: call to
> '__compiletime_assert_491' declared with attribute error: FIELD_PREP: value
> too large for the field include/linux/mfd/ti_am335x_tscadc.h:58:29: note:
> in expansion of macro 'FIELD_PREP'
>     #define STEPCONFIG_AVG(val) FIELD_PREP(GENMASK(4, 2), (val))
>                                 ^~~~~~~~~~
> drivers/iio/adc/ti_am335x_adc.c:127:17: note: in expansion of macro 'STEPCONFIG_AVG'
> 	stepconfig = STEPCONFIG_AVG(ffs(adc_dev->step_avg[i]) - 1)

A bit irritating but fair enough that the compiler would have to see a long way to know
that it always fits.

> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202510102117.Jqxrw1vF-lkp@intel.com/
> Signed-off-by: Pei Xiao <xiaopei01@...inos.cn>
> ---
>  drivers/iio/adc/ti_am335x_adc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
> index 99f274adc870..45bdd57bfdc2 100644
> --- a/drivers/iio/adc/ti_am335x_adc.c
> +++ b/drivers/iio/adc/ti_am335x_adc.c
> @@ -123,7 +123,7 @@ static void tiadc_step_config(struct iio_dev *indio_dev)
>  
>  		chan = adc_dev->channel_line[i];
>  
> -		if (adc_dev->step_avg[i])
> +		if (adc_dev->step_avg[i] && adc_dev->step_avg[i] < STEPCONFIG_AVG_16)

why < rather than <=?

STEPCONFIG_AVG_16 is the default.

>  			stepconfig = STEPCONFIG_AVG(ffs(adc_dev->step_avg[i]) - 1) |
>  				     STEPCONFIG_FIFO1;
>  		else