[PATCH 1/6] RTC: Class device support for persistent clock (#2)

From: Maciej W. Rozycki
Date: Mon May 12 2008 - 23:29:12 EST

This is a generic implementation of rtc_read_persistent_clock() and
rtc_update_persistent_clock() suitable for platforms to be used for
read_persistent_clock() and update_persistent_clock() calls. An RTC
device selected by the user with the RTC_HCTOSYS_DEVICE option is used.

As rtc_read_persistent_clock() is not available at the time
timekeeping_init() is called, it will now be disabled if the class device
is to be used as a reference. In this case rtc_hctosys(), already
present, will be used to set up the system time at the late initcall time.
This call has now been rewritten to make use of
rtc_read_persistent_clock().

As rtc_set_mmss() used by rtc_update_persistent_clock() may sleep for
some hardware, the call is now made from a work queue scheduled by the
timer originally used for the entire function. However, following
DavidW's suggestion, the mutex in rtc_set_mmss() is now obtained with
mutex_trylock() a failure of which makes the function terminate, so that
latency from the caller to the point where hardware is accessed is
minimised.

Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
---
patch-2.6.26-rc1-20080505-rtc-persistent-clock-14
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/drivers/rtc/Kconfig linux-2.6.26-rc1-20080505/drivers/rtc/Kconfig
--- linux-2.6.26-rc1-20080505.macro/drivers/rtc/Kconfig 2008-05-05 02:55:40.000000000 +0000
+++ linux-2.6.26-rc1-20080505/drivers/rtc/Kconfig 2008-05-05 21:41:34.000000000 +0000
@@ -21,24 +21,30 @@ menuconfig RTC_CLASS
if RTC_CLASS

config RTC_HCTOSYS
- bool "Set system time from RTC on startup and resume"
+ bool "Use time from RTC as a reference for the system time"
depends on RTC_CLASS = y
default y
help
- If you say yes here, the system time (wall clock) will be set using
- the value read from a specified RTC device. This is useful to avoid
- unnecessary fsck runs at boot time, and to network better.
+ If you say yes here, the specified RTC device will be used
+ as a reference to the system time (wall clock). The device
+ will be used to set the system time as required during
+ startup, suspend and, for platforms that support such usage,
+ for NTP timekeeping.
+
+ This is useful to avoid unnecessary fsck runs at boot time,
+ and to network better.

config RTC_HCTOSYS_DEVICE
- string "RTC used to set the system time"
+ string "RTC used as a reference for the system time"
depends on RTC_HCTOSYS = y
default "rtc0"
help
- The RTC device that will be used to (re)initialize the system
+ The RTC device that will be used as a reference for the system
clock, usually rtc0. Initialization is done when the system
- starts up, and when it resumes from a low power state. This
- device should record time in UTC, since the kernel won't do
- timezone correction.
+ starts up, and when it resumes from a low power state. Also,
+ if supported by the platform, NTP timekeeping uses this device
+ to record the system time periodically. This device should
+ record time in UTC, since the kernel won't do timezone correction.

The driver for this RTC device must be loaded before late_initcall
functions run, so it must usually be statically linked.
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/drivers/rtc/hctosys.c linux-2.6.26-rc1-20080505/drivers/rtc/hctosys.c
--- linux-2.6.26-rc1-20080505.macro/drivers/rtc/hctosys.c 2008-05-05 02:55:40.000000000 +0000
+++ linux-2.6.26-rc1-20080505/drivers/rtc/hctosys.c 2008-05-11 19:18:19.000000000 +0000
@@ -1,8 +1,9 @@
/*
- * RTC subsystem, initialize system time on startup
+ * RTC subsystem, persistent clock and startup initialization support
*
* Copyright (C) 2005 Tower Technologies
* Author: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
+ * Copyright (C) 2008 Maciej W. Rozycki
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
@@ -22,46 +23,86 @@
* the best guess is to add 0.5s.
*/

-static int __init rtc_hctosys(void)
+/*
+ * Note the unusual API:
+ * zero returned means a failure, anything else is seconds from epoch.
+ */
+unsigned long rtc_read_persistent_clock(void)
{
- int err;
- struct rtc_time tm;
struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
+ struct rtc_time tm;
+ unsigned long time = 0;

if (rtc == NULL) {
- printk("%s: unable to open rtc device (%s)\n",
- __FILE__, CONFIG_RTC_HCTOSYS_DEVICE);
- return -ENODEV;
+ printk(KERN_ERR "hctosys: unable to open rtc device (%s)\n",
+ CONFIG_RTC_HCTOSYS_DEVICE);
+ goto out;
+ }
+ if (rtc_read_time(rtc, &tm) < 0) {
+ dev_err(rtc->dev.parent,
+ "hctosys: unable to read the hardware clock\n");
+ goto out_close;
}
+ if (rtc_valid_tm(&tm) < 0) {
+ dev_err(rtc->dev.parent, "hctosys: invalid date/time\n");
+ goto out_close;
+ }
+
+ rtc_tm_to_time(&tm, &time);
+
+out_close:
+ rtc_class_close(rtc);
+out:
+ return time;
+}
+
+int rtc_update_persistent_clock(struct timespec now)
+{
+ struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
+ int err;

- err = rtc_read_time(rtc, &tm);
- if (err == 0) {
- err = rtc_valid_tm(&tm);
- if (err == 0) {
- struct timespec tv;
-
- tv.tv_nsec = NSEC_PER_SEC >> 1;
-
- rtc_tm_to_time(&tm, &tv.tv_sec);
-
- do_settimeofday(&tv);
-
- dev_info(rtc->dev.parent,
- "setting system clock to "
- "%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
- tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
- tm.tm_hour, tm.tm_min, tm.tm_sec,
- (unsigned int) tv.tv_sec);
- }
- else
+ if (rtc == NULL) {
+ printk(KERN_ERR "hctosys: unable to open rtc device (%s)\n",
+ CONFIG_RTC_HCTOSYS_DEVICE);
+ err = -ENXIO;
+ goto out;
+ }
+ err = rtc_set_mmss(rtc, now.tv_sec);
+ if (err < 0) {
+ if (err != -EBUSY)
dev_err(rtc->dev.parent,
- "hctosys: invalid date/time\n");
+ "hctosys: unable to set the hardware clock\n");
+ goto out_close;
}
- else
- dev_err(rtc->dev.parent,
- "hctosys: unable to read the hardware clock\n");

+ err = 0;
+
+out_close:
rtc_class_close(rtc);
+out:
+ return err;
+}
+
+static int __init rtc_hctosys(void)
+{
+ struct rtc_time tm;
+ struct timespec tv;
+ unsigned long time;
+
+ time = rtc_read_persistent_clock();
+ if (!time)
+ return -ENODEV;
+
+ tv.tv_nsec = NSEC_PER_SEC >> 1;
+ tv.tv_sec = time;
+ do_settimeofday(&tv);
+
+ rtc_time_to_tm(time, &tm);
+ pr_info("%s: setting system clock to "
+ "%d-%02d-%02d %02d:%02d:%02d UTC (%lu)\n",
+ CONFIG_RTC_HCTOSYS_DEVICE,
+ tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
+ tm.tm_hour, tm.tm_min, tm.tm_sec, (unsigned long)tv.tv_sec);

return 0;
}
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/drivers/rtc/interface.c linux-2.6.26-rc1-20080505/drivers/rtc/interface.c
--- linux-2.6.26-rc1-20080505.macro/drivers/rtc/interface.c 2008-05-05 02:55:40.000000000 +0000
+++ linux-2.6.26-rc1-20080505/drivers/rtc/interface.c 2008-05-11 19:32:40.000000000 +0000
@@ -64,8 +64,7 @@ int rtc_set_mmss(struct rtc_device *rtc,
{
int err;

- err = mutex_lock_interruptible(&rtc->ops_lock);
- if (err)
+ if (!mutex_trylock(&rtc->ops_lock))
return -EBUSY;

if (!rtc->ops)
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/include/linux/rtc.h linux-2.6.26-rc1-20080505/include/linux/rtc.h
--- linux-2.6.26-rc1-20080505.macro/include/linux/rtc.h 2008-05-05 02:55:59.000000000 +0000
+++ linux-2.6.26-rc1-20080505/include/linux/rtc.h 2008-05-05 21:10:50.000000000 +0000
@@ -200,6 +200,9 @@ extern int rtc_irq_set_state(struct rtc_
extern int rtc_irq_set_freq(struct rtc_device *rtc,
struct rtc_task *task, int freq);

+extern unsigned long rtc_read_persistent_clock(void);
+extern int rtc_update_persistent_clock(struct timespec now);
+
typedef struct rtc_task {
void (*func)(void *private_data);
void *private_data;
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/kernel/time/ntp.c linux-2.6.26-rc1-20080505/kernel/time/ntp.c
--- linux-2.6.26-rc1-20080505.macro/kernel/time/ntp.c 2008-05-05 02:56:03.000000000 +0000
+++ linux-2.6.26-rc1-20080505/kernel/time/ntp.c 2008-05-05 21:10:50.000000000 +0000
@@ -3,6 +3,8 @@
*
* NTP state machine interfaces and logic.
*
+ * Copyright (c) 2008 Maciej W. Rozycki
+ *
* This code was mainly moved from kernel/timer.c and kernel/time.c
* Please see those files for relevant copyright info and historical
* changelogs.
@@ -17,6 +19,7 @@
#include <linux/capability.h>
#include <linux/math64.h>
#include <linux/clocksource.h>
+#include <linux/workqueue.h>
#include <asm/timex.h>

/*
@@ -218,11 +221,13 @@ void second_overflow(void)
/* Disable the cmos update - used by virtualization and embedded */
int no_sync_cmos_clock __read_mostly;

-static void sync_cmos_clock(unsigned long dummy);
+static void sync_cmos_clock(unsigned long data);
+static void do_sync_cmos_clock(struct work_struct *work);

static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
+static DECLARE_WORK(sync_cmos_work, do_sync_cmos_clock);

-static void sync_cmos_clock(unsigned long dummy)
+static void do_sync_cmos_clock(struct work_struct *work)
{
struct timespec now, next;
int fail = 1;
@@ -261,6 +266,12 @@ static void sync_cmos_clock(unsigned lon
mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
}

+static void sync_cmos_clock(unsigned long data)
+{
+ /* Some implementations of update_persistent_clock() may sleep. */
+ schedule_work(&sync_cmos_work);
+}
+
static void notify_cmos_timer(void)
{
if (!no_sync_cmos_clock)
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/kernel/time/timekeeping.c linux-2.6.26-rc1-20080505/kernel/time/timekeeping.c
--- linux-2.6.26-rc1-20080505.macro/kernel/time/timekeeping.c 2008-05-05 02:56:03.000000000 +0000
+++ linux-2.6.26-rc1-20080505/kernel/time/timekeeping.c 2008-05-05 21:10:50.000000000 +0000
@@ -242,7 +242,11 @@ unsigned long __attribute__((weak)) read
void __init timekeeping_init(void)
{
unsigned long flags;
- unsigned long sec = read_persistent_clock();
+ unsigned long sec = 0;
+
+#ifndef CONFIG_RTC_HCTOSYS
+ sec = read_persistent_clock();
+#endif

write_seqlock_irqsave(&xtime_lock, flags);

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