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Subject[PATCH 3/4] ARM: mach-sa1100: Fix for a nasty initialization bug in the RTSR.
Date
This patch fixes a nasty initialization condition on the RTSR register.
Sometimes, bit 1 will wake up set, sometimes not. This can be seen
by checking the value of the RTSR by typing '$ cat /proc/driver/rtc',
which has been provided by the previous patch.

If this bit is set, the command '$ cat /dev/rtc0' will lock the system
in an endless interrupt routine calling loop.

This patch fixes the issue both at sa1100_rtc_probe(), where it avoids
a spurious interrupt from happening, and at sa1100_rtc_interrupt(),
which is the robust solution, though it does not avoid the first
spurious interrupt.

Signed-off-by: Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br>
---
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 b04c837..b0985f7 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;
}

--
1.7.0.1


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