diff options
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/kernel/time_64.c | 30 |
1 files changed, 18 insertions, 12 deletions
diff --git a/arch/x86/kernel/time_64.c b/arch/x86/kernel/time_64.c index 4ad1f7a6a83..368b1942b39 100644 --- a/arch/x86/kernel/time_64.c +++ b/arch/x86/kernel/time_64.c @@ -161,21 +161,27 @@ unsigned long read_persistent_clock(void) unsigned century = 0; 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 invalid (off bus) during update + */ + while ((CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)) + cpu_relax(); - do { - 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); + + /* now read all RTC registers while stable with interrupts disabled */ + 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); + if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID && + acpi_gbl_FADT.century) + century = CMOS_READ(acpi_gbl_FADT.century); #endif - } while (sec != CMOS_READ(RTC_SECONDS)); - spin_unlock_irqrestore(&rtc_lock, flags); /* |