linux-kernel - Re: [PATCH -next] pwm: lp3943: Fix an incorrect type in lp3943_pwm_parse

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Message-ID: <96f7b10a-e33e-4602-ab5f-4ebdac260592@kernel.org>
Date: Fri, 9 Aug 2024 10:50:49 +0200
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>,
 "Rob Herring (Arm)" <robh@...nel.org>
Cc: linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Abaci Robot <abaci@...ux.alibaba.com>
Subject: Re: [PATCH -next] pwm: lp3943: Fix an incorrect type in
 lp3943_pwm_parse_dt()

Hello Jiapeng,

On 8/9/24 10:05, Jiapeng Chong wrote:
> The return value from the call to of_property_count_u32_elems() is int.
> However, the return value is being assigned to an u32 variable
> 'num_outputs', so making 'num_outputs' an int.
> 
> ./drivers/pwm/pwm-lp3943.c:238:6-17: WARNING: Unsigned expression compared with zero: num_outputs <= 0.

Which tool does emit this warning? My test build (with C=1 and W=1) 
doesn't emit it.

> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=9710
> Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>

This problem was introduced in a commit in next:

Fixes: d6a56f3bb650 ("pwm: lp3943: Use of_property_count_u32_elems() to 
get property length")

Rob: I guess this wasn't the only conversion of this type. Maybe these 
others suffer from the same problem?!

> ---
>   drivers/pwm/pwm-lp3943.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-lp3943.c b/drivers/pwm/pwm-lp3943.c
> index f0e94c9e5956..90b0733c00c1 100644
> --- a/drivers/pwm/pwm-lp3943.c
> +++ b/drivers/pwm/pwm-lp3943.c
> @@ -218,8 +218,7 @@ static int lp3943_pwm_parse_dt(struct device *dev,
>   	struct lp3943_platform_data *pdata;
>   	struct lp3943_pwm_map *pwm_map;
>   	enum lp3943_pwm_output *output;
> -	int i, err, count = 0;
> -	u32 num_outputs;
> +	int i, err, num_outputs, count = 0;
>   
>   	if (!node)
>   		return -EINVAL;

Nitpick (maybe even a subjective one):
While touching num_outputs, its scope could be reduced to the for loop.

Best regards
Uwe