linux-kernel - Re: [PATCH v10 03/18] rtc: sun6i: Fix time overflow handling

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Date:   Tue, 22 Feb 2022 10:58:23 +0000
From:   Andre Przywara <andre.przywara@....com>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Rob Herring <robh@...nel.org>,
        Ondrej Jirman <megous@...ous.com>,
        Icenowy Zheng <icenowy@...c.io>,
        Samuel Holland <samuel@...lland.org>,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-rtc@...r.kernel.org
Subject: Re: [PATCH v10 03/18] rtc: sun6i: Fix time overflow handling

On Fri, 11 Feb 2022 12:26:28 +0000
Andre Przywara <andre.przywara@....com> wrote:

Hi Alessandro, Alexandre,

I was wondering if you would consider taking this (as a fix)?
This (time_gap > U32_MAX) comparison looks flawed by design, and we should
use time_t these days anyway.

Also, do you have an opinion on the other RTC patches? The linear day
patch (v10 04/18)[1] and the broken-down alarm registers (v10 05/18)[2]
were on the list for a while now and are needed by other SoCs as well
(R329[3] and the RISC-V D1).

Cheers,
Andre
[1] https://lore.kernel.org/linux-arm-kernel/20220211122643.1343315-5-andre.przywara@arm.com/
[2] https://lore.kernel.org/linux-arm-kernel/20220211122643.1343315-6-andre.przywara@arm.com/
[3] https://lore.kernel.org/linux-arm-kernel/20210802062212.73220-3-icenowy@sipeed.com/

> Using "unsigned long" for UNIX timestamps is never a good idea, and
> comparing the value of such a variable against U32_MAX does not do
> anything useful on 32-bit systems.
> 
> Use the proper time64_t type when dealing with timestamps, and avoid
> cutting down the time range unnecessarily. This also fixes the flawed
> check for the alarm time being too far into the future.
> 
> The check for this condition is actually somewhat theoretical, as the
> RTC counts till 2033 only anyways, and 2^32 seconds from now is not
> before the year 2157 - at which point I hope nobody will be using this
> hardware anymore.
> 
> Signed-off-by: Andre Przywara <andre.przywara@....com>
> Reviewed-by: Jernej Skrabec <jernej.skrabec@...il.com>
> ---
>  drivers/rtc/rtc-sun6i.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
> index 35b34d14a1db..dc3ae851841c 100644
> --- a/drivers/rtc/rtc-sun6i.c
> +++ b/drivers/rtc/rtc-sun6i.c
> @@ -139,7 +139,7 @@ struct sun6i_rtc_dev {
>  	const struct sun6i_rtc_clk_data *data;
>  	void __iomem *base;
>  	int irq;
> -	unsigned long alarm;
> +	time64_t alarm;
>  
>  	struct clk_hw hw;
>  	struct clk_hw *int_osc;
> @@ -511,10 +511,8 @@ static int sun6i_rtc_setalarm(struct device *dev,
> struct rtc_wkalrm *wkalrm) struct sun6i_rtc_dev *chip =
> dev_get_drvdata(dev); struct rtc_time *alrm_tm = &wkalrm->time;
>  	struct rtc_time tm_now;
> -	unsigned long time_now = 0;
> -	unsigned long time_set = 0;
> -	unsigned long time_gap = 0;
> -	int ret = 0;
> +	time64_t time_now, time_set;
> +	int ret;
>  
>  	ret = sun6i_rtc_gettime(dev, &tm_now);
>  	if (ret < 0) {
> @@ -529,9 +527,7 @@ static int sun6i_rtc_setalarm(struct device *dev,
> struct rtc_wkalrm *wkalrm) return -EINVAL;
>  	}
>  
> -	time_gap = time_set - time_now;
> -
> -	if (time_gap > U32_MAX) {
> +	if ((time_set - time_now) > U32_MAX) {
>  		dev_err(dev, "Date too far in the future\n");
>  		return -EINVAL;
>  	}
> @@ -540,7 +536,7 @@ static int sun6i_rtc_setalarm(struct device *dev,
> struct rtc_wkalrm *wkalrm) writel(0, chip->base + SUN6I_ALRM_COUNTER);
>  	usleep_range(100, 300);
>  
> -	writel(time_gap, chip->base + SUN6I_ALRM_COUNTER);
> +	writel(time_set - time_now, chip->base + SUN6I_ALRM_COUNTER);
>  	chip->alarm = time_set;
>  
>  	sun6i_rtc_setaie(wkalrm->enabled, chip);