diff options
| -rw-r--r-- | drivers/rtc/rtc-sa1100.c | 42 |
1 files changed, 41 insertions, 1 deletions
diff --git a/drivers/rtc/rtc-sa1100.c b/drivers/rtc/rtc-sa1100.c index b04c8374a279..b0985f727078 100644 --- a/drivers/rtc/rtc-sa1100.c +++ b/drivers/rtc/rtc-sa1100.c @@ -117,7 +117,23 @@ static irqreturn_t sa1100_rtc_interrupt(int irq, void *dev_id) rtsr = RTSR; /* clear interrupt sources */ RTSR = 0; - RTSR = (RTSR_AL | RTSR_HZ) & (rtsr >> 2); + /* Fix for a nasty initialization problem the in SA11xx RTSR register. + * See also the comments in sa1100_rtc_probe(). */ + if (rtsr & (RTSR_ALE | RTSR_HZE)) { + /* This is the original code, before there was the if test + * above. This code does not clear interrupts that were not + * enabled. */ + RTSR = (RTSR_AL | RTSR_HZ) & (rtsr >> 2); + } else { + /* For some reason, it is possible to enter this routine + * without interruptions enabled, it has been tested with + * several units (Bug in SA11xx chip?). + * + * This situation leads to an infinite "loop" of interrupt + * routine calling and as a result the processor seems to + * lock on its first call to open(). */ + RTSR = RTSR_AL | RTSR_HZ; + } /* clear alarm interrupt if it has occurred */ if (rtsr & RTSR_AL) @@ -382,6 +398,30 @@ static int sa1100_rtc_probe(struct platform_device *pdev) platform_set_drvdata(pdev, rtc); + /* Fix for a nasty initialization problem the in SA11xx RTSR register. + * See also the comments in sa1100_rtc_interrupt(). + * + * Sometimes bit 1 of the RTSR (RTSR_HZ) will wake up 1, which means an + * interrupt pending, even though interrupts were never enabled. + * In this case, this bit it must be reset before enabling + * interruptions to avoid a nonexistent interrupt to occur. + * + * In principle, the same problem would apply to bit 0, although it has + * never been observed to happen. + * + * This issue is addressed both here and in sa1100_rtc_interrupt(). + * If the issue is not addressed here, in the times when the processor + * wakes up with the bit set there will be one spurious interrupt. + * + * The issue is also dealt with in sa1100_rtc_interrupt() to be on the + * safe side, once the condition that lead to this strange + * initialization is unknown and could in principle happen during + * normal processing. + * + * Notice that clearing bit 1 and 0 is accomplished by writting ONES to + * the corresponding bits in RTSR. */ + RTSR = RTSR_AL | RTSR_HZ; + return 0; } |