ARM: rockchip: add option to access the pmu via a phandle in smp_operations

Makes it possible to define a rockchip,pmu phandle in the cpus node directly
referencing the pmu syscon instead of searching for specific compatible.

The old way of finding the pmu stays of course available.
Signed-off-by: NKever Yang <kever.yang@rock-chips.com>
Tested-by: NKevin Hilman <khilman@linaro.org>
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/cpus.txt

@@ -227,6 +227,15 @@ nodes to be present and contain the properties described below.
 			# List of phandles to idle state nodes supported
 			  by this cpu [3].
 
+	- rockchip,pmu
+		Usage: optional for systems that have an "enable-method"
+		       property value of "rockchip,rk3066-smp"
+		       While optional, it is the preferred way to get access to
+		       the cpu-core power-domains.
+		Value type: <phandle>
+		Definition: Specifies the syscon node controlling the cpu core
+			    power domains.
+
 Example 1 (dual-cluster big.LITTLE system 32-bit):
 
 	cpus {

arch/arm/mach-rockchip/platsmp.c

@@ -155,6 +155,19 @@ static int __init rockchip_smp_prepare_pmu(void)
 	struct device_node *node;
 	void __iomem *pmu_base;
 
+	/*
+	 * This function is only called via smp_ops->smp_prepare_cpu().
+	 * That only happens if a "/cpus" device tree node exists
+	 * and has an "enable-method" property that selects the SMP
+	 * operations defined herein.
+	 */
+	node = of_find_node_by_path("/cpus");
+
+	pmu = syscon_regmap_lookup_by_phandle(node, "rockchip,pmu");
+	of_node_put(node);
+	if (!IS_ERR(pmu))
+		return 0;
+
 	pmu = syscon_regmap_lookup_by_compatible("rockchip,rk3066-pmu");
 	if (!IS_ERR(pmu))
 		return 0;