ARM: at91: fix hanged boot due to early rtt-interrupt

Make sure the RTT-interrupts are masked at boot by adding a new helper
function to be used at SOC-init.

This fixes hanged boot on all AT91 SOCs with an RTT, for example, if an
RTT-alarm goes off after a non-clean shutdown (e.g. when using RTC
wakeup).

The RTC and RTT-peripherals are powered by backup power (VDDBU) (on all
AT91 SOCs but RM9200) and are not reset on wake-up, user, watchdog or
software reset. This means that their interrupts may be enabled during
early boot if, for example, they where not disabled during a previous
shutdown (e.g. due to a buggy driver or a non-clean shutdown such as a
user reset). Furthermore, an RTC or RTT-alarm may also be active.

The RTC and RTT-interrupts use the shared system-interrupt line, which
is also used by the PIT, and if an interrupt occurs before a handler
(e.g. RTC-driver) has been installed this leads to the system interrupt
being disabled and prevents the system from booting.

Note that when boot hangs due to an early RTC or RTT-interrupt, the only
way to get the system to start again is to remove the backup power (e.g.
battery) or to disable the interrupt manually from the bootloader. In
particular, a user reset is not sufficient.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: stable@vger.kernel.org # 3.11.x

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/arm/mach-at91/sysirq_mask.c b/arch/arm/mach-at91/sysirq_mask.c
index ee3e22c66ce8..2ba694f9626b 100644
--- a/arch/arm/mach-at91/sysirq_mask.c
+++ b/arch/arm/mach-at91/sysirq_mask.c
@@ -21,6 +21,7 @@
  */
 
 #include <linux/io.h>
+#include <mach/at91_rtt.h>
 
 #include "generic.h"
 
@@ -45,3 +46,26 @@ void __init at91_sysirq_mask_rtc(u32 rtc_base)
 
 	iounmap(base);
 }
+
+void __init at91_sysirq_mask_rtt(u32 rtt_base)
+{
+	void __iomem *base;
+	void __iomem *reg;
+	u32 mode;
+
+	base = ioremap(rtt_base, 16);
+	if (!base)
+		return;
+
+	reg = base + AT91_RTT_MR;
+
+	mode = readl_relaxed(reg);
+	if (mode & (AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN)) {
+		pr_info("AT91: Disabling rtt irq\n");
+		mode &= ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN);
+		writel_relaxed(mode, reg);
+		(void)readl_relaxed(reg);			/* flush */
+	}
+
+	iounmap(base);
+}