linux-kernel - Re: [PATCH] power: supply: remove less-than-zero comparison of unsigned variables

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Message-ID: <20221029001708.fxu6he7pbv7voiy2@mercury.elektranox.org>
Date:   Sat, 29 Oct 2022 02:17:08 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     kernel@...labora.com, kernel-janitors@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Morgan <macromorgan@...mail.com>,
        Maya Matuszczyk <maccraft123mc@...il.com>
Subject: Re: [PATCH] power: supply: remove less-than-zero comparison of
 unsigned variables

Hi,

On Tue, Oct 04, 2022 at 11:45:21AM +0500, Muhammad Usama Anjum wrote:
> max_chg_vol_reg and max_chg_cur_reg are unsigned variables. The
> less-than-zero comparison of an unsigned value is never true. Remove
> these checks.
> 
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
> ---

I'm a bit hesitant to apply this. While the analysis is correct
max_chg_cur_reg is sourced from rk817_chg_cur_to_reg(). That has
has a 'u8' return value as function signature, but tries to return
-EINVAL. I think it makes sense to either fix this at the same
time or change the variable type to signed. Also please Cc the
driver author (done now).

-- Sebastian

>  drivers/power/supply/rk817_charger.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/power/supply/rk817_charger.c b/drivers/power/supply/rk817_charger.c
> index 635f051b0821..aa4b33f1bb83 100644
> --- a/drivers/power/supply/rk817_charger.c
> +++ b/drivers/power/supply/rk817_charger.c
> @@ -951,12 +951,12 @@ static int rk817_battery_init(struct rk817_charger *charger,
>  
>  	max_chg_cur_reg = rk817_chg_cur_to_reg(max_chg_cur_ma);
>  
> -	if (max_chg_vol_reg < 0 || max_chg_vol_reg > 7) {
> +	if (max_chg_vol_reg > 7) {
>  		return dev_err_probe(charger->dev, -EINVAL,
>  		       "invalid max charger voltage, value %u unsupported\n",
>  		       max_chg_vol_mv * 1000);
>  	}
> -	if (max_chg_cur_reg < 0 || max_chg_cur_reg > 7) {
> +	if (max_chg_cur_reg > 7) {
>  		return dev_err_probe(charger->dev, -EINVAL,
>  		       "invalid max charger current, value %u unsupported\n",
>  		       max_chg_cur_ma * 1000);
> -- 
> 2.30.2
> 

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