ARM: 6454/1: sa1100: Fix for a nasty initialization bug in the RTSR.

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>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/drivers/rtc/rtc-sa1100.c b/drivers/rtc/rtc-sa1100.c
index b04c837..b0985f7 100644 (file)
--- 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;
 }