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

Make sure the RTC-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 RTC (but RM9200), for
example, after a reset during an RTC-update or if an RTC-alarm goes off
after 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

arch/arm/mach-at91/Makefile

@@ -2,7 +2,7 @@
 # Makefile for the linux kernel.
 #
 
-obj-y		:= irq.o gpio.o setup.o
+obj-y		:= irq.o gpio.o setup.o sysirq_mask.o
 obj-m		:=
 obj-n		:=
 obj-		:=

arch/arm/mach-at91/at91sam9g45.c

@@ -377,6 +377,8 @@ static void __init at91sam9g45_initialize(void)
 	arm_pm_idle = at91sam9_idle;
 	arm_pm_restart = at91sam9g45_restart;
 
+	at91_sysirq_mask_rtc(AT91SAM9G45_BASE_RTC);
+
 	/* Register GPIO subsystem */
 	at91_gpio_init(at91sam9g45_gpio, 5);
 }

arch/arm/mach-at91/at91sam9n12.c

@@ -223,7 +223,13 @@ static void __init at91sam9n12_map_io(void)
 	at91_init_sram(0, AT91SAM9N12_SRAM_BASE, AT91SAM9N12_SRAM_SIZE);
 }
 
+static void __init at91sam9n12_initialize(void)
+{
+	at91_sysirq_mask_rtc(AT91SAM9N12_BASE_RTC);
+}
+
 AT91_SOC_START(at91sam9n12)
 	.map_io = at91sam9n12_map_io,
 	.register_clocks = at91sam9n12_register_clocks,
+	.init = at91sam9n12_initialize,
 AT91_SOC_END

arch/arm/mach-at91/at91sam9rl.c

@@ -294,6 +294,8 @@ static void __init at91sam9rl_initialize(void)
 	arm_pm_idle = at91sam9_idle;
 	arm_pm_restart = at91sam9_alt_restart;
 
+	at91_sysirq_mask_rtc(AT91SAM9RL_BASE_RTC);
+
 	/* Register GPIO subsystem */
 	at91_gpio_init(at91sam9rl_gpio, 4);
 }

arch/arm/mach-at91/at91sam9x5.c

@@ -322,6 +322,11 @@ static void __init at91sam9x5_map_io(void)
 	at91_init_sram(0, AT91SAM9X5_SRAM_BASE, AT91SAM9X5_SRAM_SIZE);
 }
 
+static void __init at91sam9x5_initialize(void)
+{
+	at91_sysirq_mask_rtc(AT91SAM9X5_BASE_RTC);
+}
+
 /* --------------------------------------------------------------------
  *  Interrupt initialization
  * -------------------------------------------------------------------- */
@@ -329,4 +334,5 @@ static void __init at91sam9x5_map_io(void)
 AT91_SOC_START(at91sam9x5)
 	.map_io = at91sam9x5_map_io,
 	.register_clocks = at91sam9x5_register_clocks,
+	.init = at91sam9x5_initialize,
 AT91_SOC_END

arch/arm/mach-at91/generic.h

@@ -34,6 +34,7 @@ extern int  __init at91_aic_of_init(struct device_node *node,
 				    struct device_node *parent);
 extern int  __init at91_aic5_of_init(struct device_node *node,
 				    struct device_node *parent);
+extern void __init at91_sysirq_mask_rtc(u32 rtc_base);
 
 
  /* Timer */

arch/arm/mach-at91/include/mach/at91sam9n12.h

@@ -48,6 +48,11 @@
 #define AT91SAM9N12_BASE_USART2	0xf8024000
 #define AT91SAM9N12_BASE_USART3	0xf8028000
 
+/*
+ * System Peripherals
+ */
+#define AT91SAM9N12_BASE_RTC	0xfffffeb0
+
 /*
  * Internal Memory.
  */

arch/arm/mach-at91/include/mach/at91sam9x5.h

@@ -54,6 +54,11 @@
 #define AT91SAM9X5_BASE_USART1	0xf8020000
 #define AT91SAM9X5_BASE_USART2	0xf8024000
 
+/*
+ * System Peripherals
+ */
+#define AT91SAM9X5_BASE_RTC	0xfffffeb0
+
 /*
  * Internal Memory.
  */

arch/arm/mach-at91/include/mach/sama5d3.h

@@ -72,6 +72,11 @@
 #define SAMA5D3_BASE_USART2	0xf8020000
 #define SAMA5D3_BASE_USART3	0xf8024000
 
+/*
+ * System Peripherals
+ */
+#define SAMA5D3_BASE_RTC	0xfffffeb0
+
 /*
  * Internal Memory
  */

arch/arm/mach-at91/sama5d3.c

@@ -371,7 +371,13 @@ static void __init sama5d3_map_io(void)
 	at91_init_sram(0, SAMA5D3_SRAM_BASE, SAMA5D3_SRAM_SIZE);
 }
 
+static void __init sama5d3_initialize(void)
+{
+	at91_sysirq_mask_rtc(SAMA5D3_BASE_RTC);
+}
+
 AT91_SOC_START(sama5d3)
 	.map_io = sama5d3_map_io,
 	.register_clocks = sama5d3_register_clocks,
+	.init = sama5d3_initialize,
 AT91_SOC_END

arch/arm/mach-at91/sysirq_mask.c

@@ -0,0 +1,47 @@
+/*
+ * sysirq_mask.c - System-interrupt masking
+ *
+ * Copyright (C) 2013 Johan Hovold <jhovold@gmail.com>
+ *
+ * Functions to disable system interrupts from backup-powered peripherals.
+ *
+ * The RTC and RTT-peripherals are generally powered by backup power (VDDBU)
+ * and are not reset on wake-up, user, watchdog or software reset. This means
+ * that their interrupts may be enabled during early boot (e.g. after a user
+ * reset).
+ *
+ * As the RTC and RTT share the system-interrupt line with the PIT, an
+ * interrupt occurring before a handler has been installed would lead to the
+ * system interrupt being disabled and prevent the system from booting.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/io.h>
+
+#include "generic.h"
+
+#define AT91_RTC_IDR	0x24	/* Interrupt Disable Register */
+#define AT91_RTC_IMR	0x28	/* Interrupt Mask Register */
+
+void __init at91_sysirq_mask_rtc(u32 rtc_base)
+{
+	void __iomem *base;
+	u32 mask;
+
+	base = ioremap(rtc_base, 64);
+	if (!base)
+		return;
+
+	mask = readl_relaxed(base + AT91_RTC_IMR);
+	if (mask) {
+		pr_info("AT91: Disabling rtc irq\n");
+		writel_relaxed(mask, base + AT91_RTC_IDR);
+		(void)readl_relaxed(base + AT91_RTC_IMR);	/* flush */
+	}
+
+	iounmap(base);
+}