rockchip: Add a way to obtain the main clock device

On Rockchip SoCs we typically have a main clock device that uses the Soc
clock driver. There is also a fixed clock for the oscillator. Add a function
to obtain the core clock.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/arm/include/asm/arch-rockchip/clock.h

@@ -67,4 +67,6 @@ struct rk3288_grf;
 
 void rk3288_clk_configure_cpu(struct rk3288_cru *cru, struct rk3288_grf *grf);
 
+int rockchip_get_clk(struct udevice **devp);
+
 #endif

arch/arm/mach-rockchip/rk3288/Makefile

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier:      GPL-2.0+
 #
 
+obj-y += clk_rk3288.o
 obj-y += reset_rk3288.o
 obj-y += sdram_rk3288.o
 obj-y += syscon_rk3288.o

arch/arm/mach-rockchip/rk3288/clk_rk3288.c

@@ -0,0 +1,17 @@
+/*
+ * Copyright (C) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <syscon.h>
+#include <asm/arch/clock.h>
+
+int rockchip_get_clk(struct udevice **devp)
+{
+	return uclass_get_device_by_driver(UCLASS_CLK,
+			DM_GET_DRIVER(rockchip_rk3288_cru), devp);
+}