diff options
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/rtc/rtc-mc146818-lib.c | 70 |
1 files changed, 70 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c index d8e67a01220e..b20f4ebb2f3a 100644 --- a/drivers/rtc/rtc-mc146818-lib.c +++ b/drivers/rtc/rtc-mc146818-lib.c @@ -9,6 +9,76 @@ #endif /* + * Execute a function while the UIP (Update-in-progress) bit of the RTC is + * unset. + * + * Warning: callback may be executed more then once. + */ +bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), + void *param) +{ + int i; + unsigned long flags; + unsigned char seconds; + + for (i = 0; i < 10; i++) { + spin_lock_irqsave(&rtc_lock, flags); + + /* + * Check whether there is an update in progress during which the + * readout is unspecified. The maximum update time is ~2ms. Poll + * every msec for completion. + * + * Store the second value before checking UIP so a long lasting + * NMI which happens to hit after the UIP check cannot make + * an update cycle invisible. + */ + seconds = CMOS_READ(RTC_SECONDS); + + if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) { + spin_unlock_irqrestore(&rtc_lock, flags); + mdelay(1); + continue; + } + + /* Revalidate the above readout */ + if (seconds != CMOS_READ(RTC_SECONDS)) { + spin_unlock_irqrestore(&rtc_lock, flags); + continue; + } + + if (callback) + callback(seconds, param); + + /* + * Check for the UIP bit again. If it is set now then + * the above values may contain garbage. + */ + if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) { + spin_unlock_irqrestore(&rtc_lock, flags); + mdelay(1); + continue; + } + + /* + * A NMI might have interrupted the above sequence so check + * whether the seconds value has changed which indicates that + * the NMI took longer than the UIP bit was set. Unlikely, but + * possible and there is also virt... + */ + if (seconds != CMOS_READ(RTC_SECONDS)) { + spin_unlock_irqrestore(&rtc_lock, flags); + continue; + } + spin_unlock_irqrestore(&rtc_lock, flags); + + return true; + } + return false; +} +EXPORT_SYMBOL_GPL(mc146818_avoid_UIP); + +/* * If the UIP (Update-in-progress) bit of the RTC is set for more then * 10ms, the RTC is apparently broken or not present. */ |