clocksource/drivers/dw_apb: Add reset control

Add code to retrieve the reset property from the dw-apb timers and if
the property is available, the safe operation is to assert the timer
into reset, and followed by a deassert of the timer reset (brings the
timer out of reset).

This patch is needed for systems where the bootloader has left the timer
not used in reset.

 - Trivial conflict with commit a74bd1ad7a:
    "Convert to using %pOFn instead of device_node.name"

Reported-by: Marek Vasut <marex@denx.de>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/dw_apb_timer_of.c

@@ -22,6 +22,7 @@
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/clk.h>
+#include <linux/reset.h>
 #include <linux/sched_clock.h>
 
 static void __init timer_get_base_and_rate(struct device_node *np,
@@ -29,12 +30,23 @@ static void __init timer_get_base_and_rate(struct device_node *np,
 {
 	struct clk *timer_clk;
 	struct clk *pclk;
+	struct reset_control *rstc;
 
 	*base = of_iomap(np, 0);
 
 	if (!*base)
 		panic("Unable to map regs for %pOFn", np);
 
+	/*
+	 * Reset the timer if the reset control is available, wiping
+	 * out the state the firmware may have left it
+	 */
+	rstc = of_reset_control_get(np, NULL);
+	if (!IS_ERR(rstc)) {
+		reset_control_assert(rstc);
+		reset_control_deassert(rstc);
+	}
+
 	/*
 	 * Not all implementations use a periphal clock, so don't panic
 	 * if it's not present