ARM: picoxcell: implement watchdog restart

Allow the platform to be restarted by triggering the watchdog to expire
with the shortest possible expiry.  This should reset the CPU core and
all on-chip peripherals.

v2:	- use writel_relaxed().

Signed-off-by: Jamie Iles <jamie@jamieiles.com>

arch/arm/mach-picoxcell/common.c

@@ -7,6 +7,7 @@
  *
  * All enquiries to support@picochip.com
  */
+#include <linux/delay.h>
 #include <linux/irq.h>
 #include <linux/irqdomain.h>
 #include <linux/of.h>
@@ -23,6 +24,26 @@
 
 #include "common.h"
 
+#define WDT_CTRL_REG_EN_MASK	(1 << 0)
+#define WDT_CTRL_REG_OFFS	(0x00)
+#define WDT_TIMEOUT_REG_OFFS	(0x04)
+static void __iomem *wdt_regs;
+
+/*
+ * The machine restart method can be called from an atomic context so we won't
+ * be able to ioremap the regs then.
+ */
+static void picoxcell_setup_restart(void)
+{
+	struct device_node *np = of_find_compatible_node(NULL, NULL,
+							 "snps,dw-apb-wdg");
+	if (WARN(!np, "unable to setup watchdog restart"))
+		return;
+
+	wdt_regs = of_iomap(np, 0);
+	WARN(!wdt_regs, "failed to remap watchdog regs");
+}
+
 static struct map_desc io_map __initdata = {
 	.virtual	= PHYS_TO_IO(PICOXCELL_PERIPH_BASE),
 	.pfn		= __phys_to_pfn(PICOXCELL_PERIPH_BASE),
@@ -38,6 +59,7 @@ static void __init picoxcell_map_io(void)
 static void __init picoxcell_init_machine(void)
 {
 	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
+	picoxcell_setup_restart();
 }
 
 static const char *picoxcell_dt_match[] = {
@@ -56,6 +78,20 @@ static void __init picoxcell_init_irq(void)
 	of_irq_init(vic_of_match);
 }
 
+static void picoxcell_wdt_restart(char mode, const char *cmd)
+{
+	/*
+	 * Configure the watchdog to reset with the shortest possible timeout
+	 * and give it chance to do the reset.
+	 */
+	if (wdt_regs) {
+		writel_relaxed(WDT_CTRL_REG_EN_MASK, wdt_regs + WDT_CTRL_REG_OFFS);
+		writel_relaxed(0, wdt_regs + WDT_TIMEOUT_REG_OFFS);
+		/* No sleeping, possibly atomic. */
+		mdelay(500);
+	}
+}
+
 DT_MACHINE_START(PICOXCELL, "Picochip picoXcell")
 	.map_io		= picoxcell_map_io,
 	.nr_irqs	= NR_IRQS_LEGACY,
@@ -64,4 +100,5 @@ DT_MACHINE_START(PICOXCELL, "Picochip picoXcell")
 	.timer		= &picoxcell_timer,
 	.init_machine	= picoxcell_init_machine,
 	.dt_compat	= picoxcell_dt_match,
+	.restart	= picoxcell_wdt_restart,
 MACHINE_END