linux-kernel - Re: [PATCH][next][V2] rtc: msc313: Fix unintentional sign extension issues with left shift of a u16

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Date:   Tue, 28 Sep 2021 19:35:59 +0200
From:   Romain Perier <romain.perier@...il.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Daniel Palmer <daniel@...ngy.jp>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Nobuhiro Iwamatsu <iwamatsu@...auri.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-rtc@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next][V2] rtc: msc313: Fix unintentional sign extension
 issues with left shift of a u16

Hi,


Re-tested with rtctest and rtc-range, everything passed.



Le mar. 28 sept. 2021 à 15:46, Colin King <colin.king@...onical.com> a écrit :
>
> From: Colin Ian King <colin.king@...onical.com>
>
> Shifting the u16 value returned by readw by 16 bits to the left
> will be promoted to a 32 bit signed int and then sign-extended
> to an unsigned long. If the top bit of the readw is set then
> the shifted value will be sign extended and the top 32 bits of
> the result will be set.
>
> Fixes: be7d9c9161b9 ("rtc: Add support for the MSTAR MSC313 RTC")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Reviewed-by: Romain Perier <romain.perier@...il.com>

Thanks,
Romain

> ---
> V2: Fix identical issue in msc313_rtc_read_time too. Thanks to Daniel Palmer
>     for noticing this ommission.
> ---
>  drivers/rtc/rtc-msc313.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-msc313.c b/drivers/rtc/rtc-msc313.c
> index 5f178d29cfd8..f3fde013c4b8 100644
> --- a/drivers/rtc/rtc-msc313.c
> +++ b/drivers/rtc/rtc-msc313.c
> @@ -53,7 +53,7 @@ static int msc313_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
>         unsigned long seconds;
>
>         seconds = readw(priv->rtc_base + REG_RTC_MATCH_VAL_L)
> -                       | (readw(priv->rtc_base + REG_RTC_MATCH_VAL_H) << 16);
> +                       | ((unsigned long)readw(priv->rtc_base + REG_RTC_MATCH_VAL_H) << 16);
>
>         rtc_time64_to_tm(seconds, &alarm->time);
>
> @@ -122,7 +122,7 @@ static int msc313_rtc_read_time(struct device *dev, struct rtc_time *tm)
>                 udelay(1);
>
>         seconds = readw(priv->rtc_base + REG_RTC_CNT_VAL_L)
> -                       | (readw(priv->rtc_base + REG_RTC_CNT_VAL_H) << 16);
> +                       | ((unsigned long)readw(priv->rtc_base + REG_RTC_CNT_VAL_H) << 16);
>
>         rtc_time64_to_tm(seconds, tm);
>
> --
> 2.32.0
>