clocksource: sun5i: Add support for reset controller

The Allwinner A31 that uses this timer has the timer IP asserted in reset.
Add an optional reset property to the DT, and deassert the timer from reset if
it's there.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/allwinner,sun5i-a13-hstimer.txt

@@ -9,6 +9,9 @@ Required properties:
 		one)
 - clocks: phandle to the source clock (usually the AHB clock)
 
+Optionnal properties:
+- resets: phandle to a reset controller asserting the timer
+
 Example:
 
 timer@01c60000 {
@@ -19,4 +22,5 @@ timer@01c60000 {
 		     <0 53 1>,
 		     <0 54 1>;
 	clocks = <&ahb1_gates 19>;
+	resets = <&ahb1rst 19>;
 };

drivers/clocksource/timer-sun5i.c

@@ -16,6 +16,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/irqreturn.h>
+#include <linux/reset.h>
 #include <linux/sched_clock.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
@@ -143,6 +144,7 @@ static u64 sun5i_timer_sched_read(void)
 
 static void __init sun5i_timer_init(struct device_node *node)
 {
+	struct reset_control *rstc;
 	unsigned long rate;
 	struct clk *clk;
 	int ret, irq;
@@ -162,6 +164,10 @@ static void __init sun5i_timer_init(struct device_node *node)
 	clk_prepare_enable(clk);
 	rate = clk_get_rate(clk);
 
+	rstc = of_reset_control_get(node, NULL);
+	if (!IS_ERR(rstc))
+		reset_control_deassert(rstc);
+
 	writel(~0, timer_base + TIMER_INTVAL_LO_REG(1));
 	writel(TIMER_CTL_ENABLE | TIMER_CTL_RELOAD,
 	       timer_base + TIMER_CTL_REG(1));