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rtc: class: support hctosys from modular RTC drivers

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Due to distribution constraints it may not be possible to statically
compile the required RTC driver into the kernel.

Expand RTC_HCTOSYS support to cover all RTC devices (statically compiled
or not) by checking at the end of RTC device registration whether the
time should be synced.

Signed-off-by: Steve Muckle <smuckle@google.com>
Link: https://lore.kernel.org/r/20191106194625.116692-1-smuckle@google.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
This commit is contained in:
Steve Muckle 2019-11-06 11:46:25 -08:00 committed by Alexandre Belloni
parent 34ce29774d
commit f9b2a4d6a5
4 changed files with 61 additions and 73 deletions
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3
drivers/rtc/Kconfig
View file

@ -41,9 +41,6 @@ config RTC_HCTOSYS_DEVICE
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.
This clock should be battery-backed, so that it reads the correct
time when the system boots from a power-off state. Otherwise, your
system will need an external clock source (like an NTP server).

1
drivers/rtc/Makefile
View file

@ -6,7 +6,6 @@
ccflags-$(CONFIG_RTC_DEBUG) := -DDEBUG
obj-$(CONFIG_RTC_LIB) += lib.o
obj-$(CONFIG_RTC_HCTOSYS) += hctosys.o
obj-$(CONFIG_RTC_SYSTOHC) += systohc.o
obj-$(CONFIG_RTC_CLASS) += rtc-core.o
obj-$(CONFIG_RTC_MC146818_LIB) += rtc-mc146818-lib.o

61
drivers/rtc/class.c
View file

@ -34,6 +34,62 @@ static void rtc_device_release(struct device *dev)
#ifdef CONFIG_RTC_HCTOSYS_DEVICE
/* Result of the last RTC to system clock attempt. */
int rtc_hctosys_ret = -ENODEV;
/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
* whether it stores the most close value or the value with partial
* seconds truncated. However, it is important that we use it to store
* the truncated value. This is because otherwise it is necessary,
* in an rtc sync function, to read both xtime.tv_sec and
* xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
* of >32bits is not possible. So storing the most close value would
* slow down the sync API. So here we have the truncated value and
* the best guess is to add 0.5s.
*/
static int rtc_hctosys(void)
{
int err = -ENODEV;
struct rtc_time tm;
struct timespec64 tv64 = {
.tv_nsec = NSEC_PER_SEC >> 1,
};
struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
if (!rtc) {
pr_info("unable to open rtc device (%s)\n",
CONFIG_RTC_HCTOSYS_DEVICE);
goto err_open;
}
err = rtc_read_time(rtc, &tm);
if (err) {
dev_err(rtc->dev.parent,
"hctosys: unable to read the hardware clock\n");
goto err_read;
}
tv64.tv_sec = rtc_tm_to_time64(&tm);
#if BITS_PER_LONG == 32
if (tv64.tv_sec > INT_MAX) {
err = -ERANGE;
goto err_read;
}
#endif
err = do_settimeofday64(&tv64);
dev_info(rtc->dev.parent, "setting system clock to %ptR UTC (%lld)\n",
&tm, (long long)tv64.tv_sec);
err_read:
rtc_class_close(rtc);
err_open:
rtc_hctosys_ret = err;
return err;
}
#endif
#if defined(CONFIG_PM_SLEEP) && defined(CONFIG_RTC_HCTOSYS_DEVICE)
@ -375,6 +431,11 @@ int __rtc_register_device(struct module *owner, struct rtc_device *rtc)
dev_info(rtc->dev.parent, "registered as %s\n",
dev_name(&rtc->dev));
#ifdef CONFIG_RTC_HCTOSYS_DEVICE
if (!strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE))
rtc_hctosys();
#endif
return 0;
}
EXPORT_SYMBOL_GPL(__rtc_register_device);

69
drivers/rtc/hctosys.c
View file

@ -1,69 +0,0 @@
// SPDX-License-Identifier: GPL-2.0
/*
* RTC subsystem, initialize system time on startup
*
* Copyright (C) 2005 Tower Technologies
* Author: Alessandro Zummo <a.zummo@towertech.it>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/rtc.h>
/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
* whether it stores the most close value or the value with partial
* seconds truncated. However, it is important that we use it to store
* the truncated value. This is because otherwise it is necessary,
* in an rtc sync function, to read both xtime.tv_sec and
* xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
* of >32bits is not possible. So storing the most close value would
* slow down the sync API. So here we have the truncated value and
* the best guess is to add 0.5s.
*/
static int __init rtc_hctosys(void)
{
int err = -ENODEV;
struct rtc_time tm;
struct timespec64 tv64 = {
.tv_nsec = NSEC_PER_SEC >> 1,
};
struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
if (!rtc) {
pr_info("unable to open rtc device (%s)\n",
CONFIG_RTC_HCTOSYS_DEVICE);
goto err_open;
}
err = rtc_read_time(rtc, &tm);
if (err) {
dev_err(rtc->dev.parent,
"hctosys: unable to read the hardware clock\n");
goto err_read;
}
tv64.tv_sec = rtc_tm_to_time64(&tm);
#if BITS_PER_LONG == 32
if (tv64.tv_sec > INT_MAX) {
err = -ERANGE;
goto err_read;
}
#endif
err = do_settimeofday64(&tv64);
dev_info(rtc->dev.parent, "setting system clock to %ptR UTC (%lld)\n",
&tm, (long long)tv64.tv_sec);
err_read:
rtc_class_close(rtc);
err_open:
rtc_hctosys_ret = err;
return err;
}
late_initcall(rtc_hctosys);