linux-kernel - Re: [PATCH] clocksource: fix counter with 32bit may wrap around

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Message-ID: <CADBw62qcAvJc7asZnF=6b8oFWq1Uk2iGynaBfSH2n07p_WexsA@mail.gmail.com>
Date:   Tue, 4 Jan 2022 09:43:10 +0800
From:   Baolin Wang <baolin.wang7@...il.com>
To:     weidong guan <weidong.guanguan@...il.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "weidong.guan" <weidong.guan@...soc.com>
Subject: Re: [PATCH] clocksource: fix counter with 32bit may wrap around

Hi,

On Fri, Dec 31, 2021 at 2:03 PM weidong guan <weidong.guanguan@...il.com> wrote:
>
> From: "weidong.guan" <weidong.guan@...soc.com>
>
> When the system sleep time exceeds 30+ hours, counter with 32bit may wrap

I am curious about which condition the system can suspend for more
than 30+ hours, from my understanding, the phone will be woken up
periodically.

> around, resulting in insufficient sleep compensation time. So We should
> enable 64bit counter mode of sprd timer and use the given mult/shift
> to ensure that sufficient counts can be generated.
>
> Signed-off-by: weidong.guan <weidong.guan@...soc.com>
> ---
>  drivers/clocksource/timer-sprd.c | 31 ++++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/clocksource/timer-sprd.c b/drivers/clocksource/timer-sprd.c
> index 430cb99..7eac059 100644
> --- a/drivers/clocksource/timer-sprd.c
> +++ b/drivers/clocksource/timer-sprd.c
> @@ -30,6 +30,7 @@
>  #define TIMER_VALUE_SHDW_HI    0x1c
>
>  #define TIMER_VALUE_LO_MASK    GENMASK(31, 0)
> +#define TIMER_VALUE_64BIT_MASK GENMASK_ULL(63, 0)
>
>  static void sprd_timer_enable(void __iomem *base, u32 flag)
>  {
> @@ -57,10 +58,12 @@ static void sprd_timer_disable(void __iomem *base)
>         writel_relaxed(val, base + TIMER_CTL);
>  }
>
> -static void sprd_timer_update_counter(void __iomem *base, unsigned long cycles)
> +static void
> +sprd_timer_update_counter(void __iomem *base, unsigned long long cycles)
>  {
>         writel_relaxed(cycles & TIMER_VALUE_LO_MASK, base + TIMER_LOAD_LO);
> -       writel_relaxed(0, base + TIMER_LOAD_HI);
> +       writel_relaxed((cycles >> 32) & TIMER_VALUE_LO_MASK,
> +                       base + TIMER_LOAD_HI);
>  }
>
>  static void sprd_timer_enable_interrupt(void __iomem *base)
> @@ -82,7 +85,7 @@ static int sprd_timer_set_next_event(unsigned long cycles,
>         struct timer_of *to = to_timer_of(ce);
>
>         sprd_timer_disable(timer_of_base(to));
> -       sprd_timer_update_counter(timer_of_base(to), cycles);
> +       sprd_timer_update_counter(timer_of_base(to), (u64)cycles);
>         sprd_timer_enable(timer_of_base(to), 0);
>
>         return 0;
> @@ -93,7 +96,8 @@ static int sprd_timer_set_periodic(struct clock_event_device *ce)
>         struct timer_of *to = to_timer_of(ce);
>
>         sprd_timer_disable(timer_of_base(to));
> -       sprd_timer_update_counter(timer_of_base(to), timer_of_period(to));
> +       sprd_timer_update_counter(timer_of_base(to),
> +                                 (u64)timer_of_period(to));
>         sprd_timer_enable(timer_of_base(to), TIMER_CTL_PERIOD_MODE);
>
>         return 0;
> @@ -162,15 +166,19 @@ static int __init sprd_timer_init(struct device_node *np)
>
>  static u64 sprd_suspend_timer_read(struct clocksource *cs)
>  {
> -       return ~(u64)readl_relaxed(timer_of_base(&suspend_to) +
> -                                  TIMER_VALUE_SHDW_LO) & cs->mask;
> +       u64 value_hi, value_lo;
> +
> +       value_hi = (u64)readl_relaxed(timer_of_base(&suspend_to) + TIMER_VALUE_SHDW_HI);
> +       value_lo = (u64)readl_relaxed(timer_of_base(&suspend_to) + TIMER_VALUE_SHDW_LO);
> +       return ~(u64)((value_hi << 32) + value_lo) & cs->mask;
>  }
>
>  static int sprd_suspend_timer_enable(struct clocksource *cs)
>  {
>         sprd_timer_update_counter(timer_of_base(&suspend_to),
> -                                 TIMER_VALUE_LO_MASK);
> -       sprd_timer_enable(timer_of_base(&suspend_to), TIMER_CTL_PERIOD_MODE);
> +                                 TIMER_VALUE_64BIT_MASK);
> +       sprd_timer_enable(timer_of_base(&suspend_to),
> +                         TIMER_CTL_PERIOD_MODE|TIMER_CTL_64BIT_WIDTH);
>
>         return 0;
>  }
> @@ -183,10 +191,12 @@ static void sprd_suspend_timer_disable(struct clocksource *cs)
>  static struct clocksource suspend_clocksource = {
>         .name   = "sprd_suspend_timer",
>         .rating = 200,
> +       .mult   = 0x1DCD650,
> +       .shift  = 10,

And why?

>         .read   = sprd_suspend_timer_read,
>         .enable = sprd_suspend_timer_enable,
>         .disable = sprd_suspend_timer_disable,
> -       .mask   = CLOCKSOURCE_MASK(32),
> +       .mask   = CLOCKSOURCE_MASK(64),
>         .flags  = CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_SUSPEND_NONSTOP,
>  };
>
> @@ -198,8 +208,7 @@ static int __init sprd_suspend_timer_init(struct device_node *np)
>         if (ret)
>                 return ret;
>
> -       clocksource_register_hz(&suspend_clocksource,
> -                               timer_of_rate(&suspend_to));
> +       clocksource_register_hz(&suspend_clocksource, 0);

-- 
Baolin Wang