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Date: Mon, 15 Aug 2022 08:49:04 -0000
From: tip-bot2 for Mateusz Jończyk
<tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: mat.jonczyk@...pl, Ingo Molnar <mingo@...nel.org>,
Alexandre Belloni <alexandre.belloni@...tlin.com>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/timers] x86/rtc: Rewrite & simplify mach_get_cmos_time() by
deleting duplicated functionality
The following commit has been merged into the x86/timers branch of tip:
Commit-ID: fc04b2ccf0edc49e53d2e1251d122e40285233e6
Gitweb: https://git.kernel.org/tip/fc04b2ccf0edc49e53d2e1251d122e40285233e6
Author: Mateusz Jończyk <mat.jonczyk@...pl>
AuthorDate: Sat, 13 Aug 2022 15:10:33 +02:00
Committer: Ingo Molnar <mingo@...nel.org>
CommitterDate: Sun, 14 Aug 2022 11:24:08 +02:00
x86/rtc: Rewrite & simplify mach_get_cmos_time() by deleting duplicated functionality
There are functions in drivers/rtc/rtc-mc146818-lib.c that handle
reading from / writing to the CMOS RTC clock. mach_get_cmos_time() in
arch/x86/kernel/rtc.c did not use them and was mostly a duplicate of
mc146818_get_time(). Modify mach_get_cmos_time() to use
mc146818_get_time() and remove the duplicated functionality.
mach_get_cmos_time() used a different algorithm than
mc146818_get_time(), but these functions are equivalent. The major
differences are:
- mc146818_get_time() is better refined and handles various edge
conditions,
- when the UIP ("Update in progress") bit of the RTC is set,
mach_get_cmos_time() was busy waiting with cpu_relax() while
mc146818_get_time() is using mdelay(1) in every loop iteration.
(However, there is my commit merged for Linux 5.20 / 6.0 to decrease
this period to 100us:
commit d2a632a8a117 ("rtc: mc146818-lib: reduce RTC_UIP polling period")
),
- mach_get_cmos_time() assumed that the RTC year is >= 2000, which
may not be true on some old boxes with a dead battery,
- mach_get_cmos_time() was holding the rtc_lock for a long time
and could hang if the RTC is broken or not present.
The RTC writing counterpart, mach_set_rtc_mmss() is already using
mc146818_get_time() from drivers/rtc. This was done in
commit 3195ef59cb42 ("x86: Do full rtc synchronization with ntp")
It appears that mach_get_cmos_time() was simply forgotten.
mach_get_cmos_time() is really used only in read_persistent_clock64(),
which is called only in a few places in kernel/time/timekeeping.c .
[ mingo: These changes are not supposed to change behavior, but they are
not identity transformations either, as mc146818_get_time() is a
better but different implementation of the same logic - so
regressions are possible in principle. ]
Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
Link: https://lore.kernel.org/r/20220813131034.768527-1-mat.jonczyk@o2.pl
---
arch/x86/kernel/rtc.c | 59 ++++--------------------------------------
1 file changed, 7 insertions(+), 52 deletions(-)
diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index 586f718..1cadc8a 100644
--- a/arch/x86/kernel/rtc.c
+++ b/arch/x86/kernel/rtc.c
@@ -4,11 +4,8 @@
*/
#include <linux/platform_device.h>
#include <linux/mc146818rtc.h>
-#include <linux/acpi.h>
-#include <linux/bcd.h>
#include <linux/export.h>
#include <linux/pnp.h>
-#include <linux/of.h>
#include <asm/vsyscall.h>
#include <asm/x86_init.h>
@@ -20,15 +17,12 @@
/*
* This is a special lock that is owned by the CPU and holds the index
* register we are working with. It is required for NMI access to the
- * CMOS/RTC registers. See include/asm-i386/mc146818rtc.h for details.
+ * CMOS/RTC registers. See arch/x86/include/asm/mc146818rtc.h for details.
*/
volatile unsigned long cmos_lock;
EXPORT_SYMBOL(cmos_lock);
#endif /* CONFIG_X86_32 */
-/* For two digit years assume time is always after that */
-#define CMOS_YEARS_OFFS 2000
-
DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL(rtc_lock);
@@ -62,8 +56,7 @@ int mach_set_rtc_mmss(const struct timespec64 *now)
void mach_get_cmos_time(struct timespec64 *now)
{
- unsigned int status, year, mon, day, hour, min, sec, century = 0;
- unsigned long flags;
+ struct rtc_time tm;
/*
* If pm_trace abused the RTC as storage, set the timespec to 0,
@@ -74,51 +67,13 @@ void mach_get_cmos_time(struct timespec64 *now)
return;
}
- spin_lock_irqsave(&rtc_lock, flags);
-
- /*
- * If UIP is clear, then we have >= 244 microseconds before
- * RTC registers will be updated. Spec sheet says that this
- * is the reliable way to read RTC - registers. If UIP is set
- * then the register access might be invalid.
- */
- while ((CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
- cpu_relax();
-
- sec = CMOS_READ(RTC_SECONDS);
- min = CMOS_READ(RTC_MINUTES);
- hour = CMOS_READ(RTC_HOURS);
- day = CMOS_READ(RTC_DAY_OF_MONTH);
- mon = CMOS_READ(RTC_MONTH);
- year = CMOS_READ(RTC_YEAR);
-
-#ifdef CONFIG_ACPI
- if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
- acpi_gbl_FADT.century)
- century = CMOS_READ(acpi_gbl_FADT.century);
-#endif
-
- status = CMOS_READ(RTC_CONTROL);
- WARN_ON_ONCE(RTC_ALWAYS_BCD && (status & RTC_DM_BINARY));
-
- spin_unlock_irqrestore(&rtc_lock, flags);
-
- if (RTC_ALWAYS_BCD || !(status & RTC_DM_BINARY)) {
- sec = bcd2bin(sec);
- min = bcd2bin(min);
- hour = bcd2bin(hour);
- day = bcd2bin(day);
- mon = bcd2bin(mon);
- year = bcd2bin(year);
+ if (mc146818_get_time(&tm)) {
+ pr_err("Unable to read current time from RTC\n");
+ now->tv_sec = now->tv_nsec = 0;
+ return;
}
- if (century) {
- century = bcd2bin(century);
- year += century * 100;
- } else
- year += CMOS_YEARS_OFFS;
-
- now->tv_sec = mktime64(year, mon, day, hour, min, sec);
+ now->tv_sec = rtc_tm_to_time64(&tm);
now->tv_nsec = 0;
}
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