From e5909c170bde83b730e6d056e9081199d9f7d69d Mon Sep 17 00:00:00 2001
From: ian <ian@FreeBSD.org>
Date: Mon, 12 Feb 2018 17:33:14 +0000
Subject: [PATCH] Add a set of convenience routines for RTC drivers to use for
 debug output, and a debug.clock_show_io sysctl to control debugging output.

---
 sys/kern/subr_rtc.c | 58 +++++++++++++++++++++++++++++++++++++++++++++
 sys/sys/clock.h     | 12 ++++++++++
 2 files changed, 70 insertions(+)

diff --git a/sys/kern/subr_rtc.c b/sys/kern/subr_rtc.c
index 34a30879f47c..6440fe66f25f 100644
--- a/sys/kern/subr_rtc.c
+++ b/sys/kern/subr_rtc.c
@@ -76,6 +76,10 @@ __FBSDID("$FreeBSD$");
 
 #include "clock_if.h"
 
+static int show_io;
+SYSCTL_INT(_debug, OID_AUTO, clock_show_io, CTLFLAG_RWTUN, &show_io, 0,
+    "Enable debug printing of RTC clock I/O; 1=reads, 2=writes, 3=both.");
+
 /* XXX: should be kern. now, it's no longer machdep.  */
 static int disable_rtc_set;
 SYSCTL_INT(_machdep, OID_AUTO, disable_rtc_set, CTLFLAG_RW, &disable_rtc_set,
@@ -144,6 +148,60 @@ settime_task_func(void *arg, int pending)
 	CLOCK_SETTIME(rtc->clockdev, &ts);
 }
 
+static void
+clock_dbgprint_hdr(device_t dev, int rw)
+{
+    struct timespec now;
+
+    getnanotime(&now);
+    device_printf(dev, "%s at ", (rw & CLOCK_DBG_READ) ? "read " : "write");
+    clock_print_ts(&now, 9);
+    printf(": "); 
+}
+
+void
+clock_dbgprint_bcd(device_t dev, int rw, const struct bcd_clocktime *bct)
+{
+
+    if (show_io & rw) {
+	clock_dbgprint_hdr(dev, rw);
+	clock_print_bcd(bct, 9);
+	printf("\n");
+    }
+}
+
+void
+clock_dbgprint_ct(device_t dev, int rw, const struct clocktime *ct)
+{
+
+    if (show_io & rw) {
+	clock_dbgprint_hdr(dev, rw);
+	clock_print_ct(ct, 9);
+	printf("\n");
+    }
+}
+
+void
+clock_dbgprint_err(device_t dev, int rw, int err)
+{
+
+    if (show_io & rw) {
+	clock_dbgprint_hdr(dev, rw);
+	printf("error = %d\n", err);
+    }
+}
+
+void
+clock_dbgprint_ts(device_t dev, int rw, const struct timespec *ts)
+{
+
+    if (show_io & rw) {
+	clock_dbgprint_hdr(dev, rw);
+	clock_print_ts(ts, 9);
+	printf("\n");
+    }
+}
+
 void
 clock_register_flags(device_t clockdev, long resolution, int flags)
 {
diff --git a/sys/sys/clock.h b/sys/sys/clock.h
index a5e89746d488..bfbd6efd2ad3 100644
--- a/sys/sys/clock.h
+++ b/sys/sys/clock.h
@@ -191,6 +191,18 @@ void clock_print_bcd(const struct bcd_clocktime *bct, int nsdig);
 void clock_print_ct(const struct clocktime *ct, int nsdig);
 void clock_print_ts(const struct timespec  *ts, int nsdig);
 
+/*
+ * Debugging helpers for RTC clock drivers.  Print a [bcd_]clocktime or
+ * timespec, only if rtc clock debugging has been enabled.  The rw argument is
+ * one of CLOCK_DBG_READ or CLOCK_DBG_WRITE.
+ */
+#define	CLOCK_DBG_READ	0x01
+#define	CLOCK_DBG_WRITE	0x02
+void clock_dbgprint_bcd(device_t dev, int rw, const struct bcd_clocktime *bct);
+void clock_dbgprint_ct(device_t dev, int rw, const struct clocktime *ct);
+void clock_dbgprint_err(device_t dev, int rw, int err);
+void clock_dbgprint_ts(device_t dev, int rw, const struct timespec *ts);
+
 #endif /* _KERNEL */
 
 #endif /* !_SYS_CLOCK_H_ */