linux-kernel - Re: [PATCH] hwmon: (nct6775) Fix incorrect parenthesization in nct6775_write_fan

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Message-ID: <20230103212037.GA213138@roeck-us.net>
Date:   Tue, 3 Jan 2023 13:20:37 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Zev Weiss <zev@...ilderbeest.net>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        Joel Stanley <joel@....id.au>,
        Denis Pauk <pauk.denis@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] hwmon: (nct6775) Fix incorrect parenthesization in
 nct6775_write_fan_div()

On Mon, Jan 02, 2023 at 01:28:57PM -0800, Zev Weiss wrote:
> Commit 4ef2774511dc ("hwmon: (nct6775) Convert register access to
> regmap API") fumbled the shifting & masking of the fan_div values such
> that odd-numbered fan divisors would always be set to zero.  Fix it so
> that we actually OR in the bits we meant to.
> 
> Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
> Fixes: 4ef2774511dc ("hwmon: (nct6775) Convert register access to regmap API")
> Cc: stable@...nel.org # v5.19+

Applied.

Thanks,
Guenter

> ---
> 
> This bug got noticed during review [0] and the fix was incorporated
> into v3 of the patch series [1], but then I somehow managed to
> accidentally revert the fix in v4 [2] that actually got applied.
> 
> I'm fairly confident this is correct, but I don't have any nct6775
> hardware to test on (this code path is only used on that specific
> chip, not others in the family).  If any one who does can try it out
> and report back that would of course be welcome.
> 
> [0] https://lore.kernel.org/linux-hwmon/YiiMfJV3bjUmoUcV@hatter.bewilderbeest.net/
> [1] https://lore.kernel.org/linux-hwmon/20220426071848.11619-3-zev@bewilderbeest.net/
> [2] https://lore.kernel.org/linux-hwmon/20220427010154.29749-3-zev@bewilderbeest.net/
> 
>  drivers/hwmon/nct6775-core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/nct6775-core.c b/drivers/hwmon/nct6775-core.c
> index da9ec6983e13..c54233f0369b 100644
> --- a/drivers/hwmon/nct6775-core.c
> +++ b/drivers/hwmon/nct6775-core.c
> @@ -1150,7 +1150,7 @@ static int nct6775_write_fan_div(struct nct6775_data *data, int nr)
>  	if (err)
>  		return err;
>  	reg &= 0x70 >> oddshift;
> -	reg |= data->fan_div[nr] & (0x7 << oddshift);
> +	reg |= (data->fan_div[nr] & 0x7) << oddshift;
>  	return nct6775_write_value(data, fandiv_reg, reg);
>  }
>