linux-kernel - [DEBUG PATCH v5] rtc-cmos: cmos_read

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Date:   Fri,  7 Jan 2022 13:51:36 +0100
From:   Mateusz Jończyk <mat.jonczyk@...pl>
To:     linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Mateusz Jończyk <mat.jonczyk@...pl>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: [DEBUG PATCH v5] rtc-cmos: cmos_read_alarm bug demonstration

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@...pl>
Cc: Alessandro Zummo <a.zummo@...ertech.it>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
---

v5: Update to apply cleanly

 drivers/rtc/rtc-cmos.c | 59 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index b90a603d6b12..9baf91fc2c41 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)
 {
 	int ret;
@@ -237,6 +242,7 @@ static int cmos_read_time(struct device *dev, struct rtc_time *t)
 		return ret;
 	}
 
+	cmos_read_alarm_uip_debugging(dev);
 	return 0;
 }
 
@@ -319,6 +325,59 @@ 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