[TEST PATCH] rtc-cmos: cmos_read_alarm bug demonstration

Mateusz Jończyk
2021-10-17T19:42:07Z

Before my commit "rtc-cmos: dont touch alarm registers during update",
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.

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 f353a41dfe8c..c24465f7bed4 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)
{
/*
@@ -234,6 +239,8 @@ static int cmos_read_time(struct device *dev, struct rtc_time *t)
* That'll make Y3K compatility (year > 2070) easy!
*/
mc146818_get_time(t);
+
+ cmos_read_alarm_uip_debugging(dev);
return 0;
}

@@ -348,6 +355,60 @@ 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