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    Subject[DEBUG PATCH v3] rtc-cmos: cmos_read_alarm bug demonstration
    Date
    Before my commit "rtc-cmos: avoid UIP when reading alarm time",
    applying this patch and reading the CMOS time like so:

    while true; do cat /sys/class/rtc/rtc0/time ; sleep 0.5; done

    produces errors in dmesg on my Intel Kaby Lake laptop.

    Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
    Cc: Alessandro Zummo <a.zummo@towertech.it>
    Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
    ---
    drivers/rtc/rtc-cmos.c | 61 ++++++++++++++++++++++++++++++++++++++++++
    1 file changed, 61 insertions(+)

    diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
    index b6d7dd3cf066..3de049930745 100644
    --- a/drivers/rtc/rtc-cmos.c
    +++ b/drivers/rtc/rtc-cmos.c
    @@ -43,6 +43,9 @@
    #include <linux/dmi.h>
    #endif

    +#include <linux/ktime.h>
    +#include <linux/timekeeping.h>
    +
    /* this is for "generic access to PC-style RTC" using CMOS_READ/CMOS_WRITE */
    #include <linux/mc146818rtc.h>

    @@ -220,6 +223,8 @@ static inline void cmos_write_bank2(unsigned char val, unsigned char addr)

    /*----------------------------------------------------------------*/

    +static void cmos_read_alarm_uip_debugging(struct device *dev);
    +
    static int cmos_read_time(struct device *dev, struct rtc_time *t)
    {
    /*
    @@ -230,6 +235,8 @@ static int cmos_read_time(struct device *dev, struct rtc_time *t)
    return -EIO;

    mc146818_get_time(t);
    +
    + cmos_read_alarm_uip_debugging(dev);
    return 0;
    }

    @@ -338,6 +345,60 @@ static int cmos_read_alarm(struct device *dev, struct rtc_wkalrm *t)
    return 0;
    }

    +static void cmos_read_alarm_uip_debugging(struct device *dev)
    +{
    + unsigned long flags;
    + unsigned char rtc_uip_baseline, rtc_uip;
    + struct rtc_wkalrm t_baseline, t;
    + ktime_t time_start, time_end;
    + int i;
    +
    + spin_lock_irqsave(&rtc_lock, flags);
    + rtc_uip_baseline = CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP;
    + spin_unlock_irqrestore(&rtc_lock, flags);
    +
    + cmos_read_alarm(dev, &t_baseline);
    +
    + time_start = ktime_get();
    +
    + for (i = 0; i < 2000; i++) {
    + spin_lock_irqsave(&rtc_lock, flags);
    + rtc_uip = CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP;
    + spin_unlock_irqrestore(&rtc_lock, flags);
    +
    + cmos_read_alarm(dev, &t);
    +
    + if (t_baseline.time.tm_sec != t.time.tm_sec) {
    + dev_err(dev,
    + "Inconsistent alarm tm_sec value: %d != %d (RTC_UIP = %d; %d)\n",
    + t_baseline.time.tm_sec,
    + t.time.tm_sec,
    + rtc_uip_baseline, rtc_uip);
    + }
    + if (t_baseline.time.tm_min != t.time.tm_min) {
    + dev_err(dev,
    + "Inconsistent alarm tm_min value: %d != %d (RTC_UIP = %d; %d)\n",
    + t_baseline.time.tm_min,
    + t.time.tm_min,
    + rtc_uip_baseline, rtc_uip);
    + }
    + if (t_baseline.time.tm_hour != t.time.tm_hour) {
    + dev_err(dev,
    + "Inconsistent alarm tm_hour value: %d != %d (RTC_UIP = %d; %d)\n",
    + t_baseline.time.tm_hour,
    + t.time.tm_hour,
    + rtc_uip_baseline, rtc_uip);
    + }
    +
    + }
    +
    + time_end = ktime_get();
    +
    + pr_info_ratelimited("%s: loop executed in %lld ns\n",
    + __func__, ktime_to_ns(ktime_sub(time_end, time_start)));
    +}
    +
    +
    static void cmos_checkintr(struct cmos_rtc *cmos, unsigned char rtc_control)
    {
    unsigned char rtc_intr;
    --
    2.25.1
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