linux-kernel - Re: [PATCH v2] iio: adc: MCP3564: fix warn: unsigned '_

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Date:   Sat, 14 Oct 2023 17:17:52 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     <marius.cristea@...rochip.com>
Cc:     <lars@...afoo.de>, <lgirdwood@...il.com>, <broonie@...nel.org>,
        <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iio: adc: MCP3564: fix warn: unsigned '__x' is never
 less than zero.

On Fri, 13 Oct 2023 16:23:33 +0300
<marius.cristea@...rochip.com> wrote:

> From: Marius Cristea <marius.cristea@...rochip.com>
> 
> The patch 33ec3e5fc1ea: "iio: adc: adding support for MCP3564 ADC"
> leads to the following Smatch static checker warning:
> 
>    smatch warnings:
>    drivers/iio/adc/mcp3564.c:1105 mcp3564_fill_scale_tbls() warn: unsigned '__x' is never less than zero.
> 
> vim +/__x +1105 drivers/iio/adc/mcp3564.c
> 
>    1094
>    1095  static void mcp3564_fill_scale_tbls(struct mcp3564_state *adc)
>    1096  {
>    .....
>    1103          for (i = 0; i < MCP3564_MAX_PGA; i++) {
>    1104                  ref = adc->vref_mv;
>  > 1105                  tmp1 = shift_right((u64)ref * NANO, pow);  
>    1106                  div_u64_rem(tmp1, NANO, &tmp0);
>    1107
>    .....
>    1113  }
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202309280738.NWjVfVt4-lkp@intel.com/
> Fixes: 33ec3e5fc1ea (iio: adc: adding support for MCP3564 ADC)
> Signed-off-by: Marius Cristea <marius.cristea@...rochip.com>
Applied to the togreg branch of iio.git and pushed out as testing briefly
for 0-day to take a look.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/mcp3564.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/mcp3564.c b/drivers/iio/adc/mcp3564.c
> index 9ede1a5d5d7b..e3f1de5fcc5a 100644
> --- a/drivers/iio/adc/mcp3564.c
> +++ b/drivers/iio/adc/mcp3564.c
> @@ -1102,7 +1102,7 @@ static void mcp3564_fill_scale_tbls(struct mcp3564_state *adc)
>  
>  	for (i = 0; i < MCP3564_MAX_PGA; i++) {
>  		ref = adc->vref_mv;
> -		tmp1 = shift_right((u64)ref * NANO, pow);
> +		tmp1 = ((u64)ref * NANO) >> pow;
>  		div_u64_rem(tmp1, NANO, &tmp0);
>  
>  		tmp1 = tmp1 * mcp3564_hwgain_frac[(2 * i) + 1];
> 
> base-commit: 5e99f692d4e32e3250ab18d511894ca797407aec