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author | Mateusz Jończyk <mat.jonczyk@o2.pl> | 2022-08-13 15:10:33 +0200 |
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committer | Ingo Molnar <mingo@kernel.org> | 2022-08-14 11:24:08 +0200 |
commit | fc04b2ccf0edc49e53d2e1251d122e40285233e6 (patch) | |
tree | 266068b74f05eec224fe813e96bd18754d498853 /arch/x86/kernel/rtc.c | |
parent | ffcf9c5700e49c0aee42dcba9a12ba21338e8136 (diff) | |
download | linux-stable-fc04b2ccf0edc49e53d2e1251d122e40285233e6.tar.gz linux-stable-fc04b2ccf0edc49e53d2e1251d122e40285233e6.tar.bz2 linux-stable-fc04b2ccf0edc49e53d2e1251d122e40285233e6.zip |
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@o2.pl>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220813131034.768527-1-mat.jonczyk@o2.pl
Diffstat (limited to 'arch/x86/kernel/rtc.c')
-rw-r--r-- | arch/x86/kernel/rtc.c | 59 |
1 files changed, 7 insertions, 52 deletions
diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c index 586f718b8e95..1cadc8a15267 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; } |