timer: Support clocks via phandle

Earlier timer driver needed a clock-frequency property in compatible
device-tree nodes. Another way is to reference a clock via a phandle.

So now timer_pre_probe tries to get clock by reference through device
tree. In case it is impossible to get clock device through the
reference, clock-frequency property of the timer node is read to provide
backward compatibility.

Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/timer/timer-uclass.c

@@ -8,6 +8,7 @@
 #include <dm.h>
 #include <dm/lists.h>
 #include <dm/device-internal.h>
+#include <clk.h>
 #include <errno.h>
 #include <timer.h>
 
@@ -42,9 +43,19 @@ unsigned long notrace timer_get_rate(struct udevice *dev)
 static int timer_pre_probe(struct udevice *dev)
 {
 	struct timer_dev_priv *uc_priv = dev_get_uclass_priv(dev);
-
-	uc_priv->clock_rate = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
-					     "clock-frequency", 0);
+	struct clk timer_clk;
+	int err;
+	ulong ret;
+
+	err = clk_get_by_index(dev, 0, &timer_clk);
+	if (!err) {
+		ret = clk_get_rate(&timer_clk);
+		if (IS_ERR_VALUE(ret))
+			return ret;
+		uc_priv->clock_rate = ret;
+	} else
+		uc_priv->clock_rate = fdtdec_get_int(gd->fdt_blob,
+				dev->of_offset,	"clock-frequency", 0);
 
 	return 0;
 }