From fc04b2ccf0edc49e53d2e1251d122e40285233e6 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= Date: Sat, 13 Aug 2022 15:10:33 +0200 Subject: [PATCH 1/2] x86/rtc: Rewrite & simplify mach_get_cmos_time() by deleting duplicated functionality MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Ingo Molnar Acked-by: Alexandre Belloni 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 586f718b8e95..1cadc8a15267 100644 --- a/arch/x86/kernel/rtc.c +++ b/arch/x86/kernel/rtc.c @@ -4,11 +4,8 @@ */ #include #include -#include -#include #include #include -#include #include #include @@ -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; } From e1a6bc7c6969527dbe0afa4801a0237e41e26b1b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= Date: Sat, 13 Aug 2022 15:10:34 +0200 Subject: [PATCH 2/2] x86/rtc: Rename mach_set_rtc_mmss() to mach_set_cmos_time() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Once upon a time, before this commit in 2013: 3195ef59cb42 ("x86: Do full rtc synchronization with ntp") ... the mach_set_rtc_mmss() function set only the minutes and seconds registers of the CMOS RTC - hence the '_mmss' postfix. This is no longer true, so rename the function to mach_set_cmos_time(). [ mingo: Expanded changelog a bit. ] Signed-off-by: Mateusz Jończyk Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20220813131034.768527-2-mat.jonczyk@o2.pl --- arch/x86/include/asm/mc146818rtc.h | 2 +- arch/x86/kernel/rtc.c | 4 ++-- arch/x86/kernel/x86_init.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/mc146818rtc.h b/arch/x86/include/asm/mc146818rtc.h index 97198001e567..6115bb3d5795 100644 --- a/arch/x86/include/asm/mc146818rtc.h +++ b/arch/x86/include/asm/mc146818rtc.h @@ -95,7 +95,7 @@ static inline unsigned char current_lock_cmos_reg(void) unsigned char rtc_cmos_read(unsigned char addr); void rtc_cmos_write(unsigned char val, unsigned char addr); -extern int mach_set_rtc_mmss(const struct timespec64 *now); +extern int mach_set_cmos_time(const struct timespec64 *now); extern void mach_get_cmos_time(struct timespec64 *now); #define RTC_IRQ 8 diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c index 1cadc8a15267..349046434513 100644 --- a/arch/x86/kernel/rtc.c +++ b/arch/x86/kernel/rtc.c @@ -27,13 +27,13 @@ DEFINE_SPINLOCK(rtc_lock); EXPORT_SYMBOL(rtc_lock); /* - * In order to set the CMOS clock precisely, set_rtc_mmss has to be + * In order to set the CMOS clock precisely, mach_set_cmos_time has to be * called 500 ms after the second nowtime has started, because when * nowtime is written into the registers of the CMOS clock, it will * jump to the next second precisely 500 ms later. Check the Motorola * MC146818A or Dallas DS12887 data sheet for details. */ -int mach_set_rtc_mmss(const struct timespec64 *now) +int mach_set_cmos_time(const struct timespec64 *now) { unsigned long long nowtime = now->tv_sec; struct rtc_time tm; diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c index e84ee5cdbd8c..57353519bc11 100644 --- a/arch/x86/kernel/x86_init.c +++ b/arch/x86/kernel/x86_init.c @@ -138,7 +138,7 @@ struct x86_platform_ops x86_platform __ro_after_init = { .calibrate_cpu = native_calibrate_cpu_early, .calibrate_tsc = native_calibrate_tsc, .get_wallclock = mach_get_cmos_time, - .set_wallclock = mach_set_rtc_mmss, + .set_wallclock = mach_set_cmos_time, .iommu_shutdown = iommu_shutdown_noop, .is_untracked_pat_range = is_ISA_range, .nmi_init = default_nmi_init,