allwinner: Scan AXP803 FDT node to setup initial power rails

Now that we have a pointer to the device tree blob, let's use that to
do some initial setup of the PMIC:
- We scan the DT for the compatible string to find the PMIC node.
- We switch the N_VBUSEN pin if the DT property tells us so.
- We scan over all regulator subnodes, and switch DC1SW if there is at
least one other node referencing it (judging by the existence of a
phandle property in that subnode).
This is just the first part of the setup, a follow up patch will setup
voltages.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

plat/allwinner/sun50i_a64/sunxi_power.c

@@ -10,6 +10,7 @@
 #include <debug.h>
 #include <delay_timer.h>
 #include <errno.h>
+#include <libfdt.h>
 #include <mmio.h>
 #include <platform_def.h>
 #include <sunxi_def.h>
@@ -126,6 +127,52 @@ static int axp_setbits(uint8_t reg, uint8_t set_mask)
 	return rsb_write(AXP803_RT_ADDR, reg, regval);
 }
 
+static bool should_enable_regulator(const void *fdt, int node)
+{
+	if (fdt_getprop(fdt, node, "phandle", NULL) != NULL)
+		return true;
+	if (fdt_getprop(fdt, node, "regulator-always-on", NULL) != NULL)
+		return true;
+	return false;
+}
+
+static void setup_axp803_rails(const void *fdt)
+{
+	int node;
+
+	/* locate the PMIC DT node, bail out if not found */
+	node = fdt_node_offset_by_compatible(fdt, -1, "x-powers,axp803");
+	if (node == -FDT_ERR_NOTFOUND) {
+		WARN("BL31: PMIC: No AXP803 DT node, skipping initial setup.\n");
+		return;
+	}
+
+	if (fdt_getprop(fdt, node, "x-powers,drive-vbus-en", NULL))
+		axp_setbits(0x8f, BIT(4));
+
+	/* descend into the "regulators" subnode */
+	node = fdt_first_subnode(fdt, node);
+
+	/* iterate over all regulators to find used ones */
+	for (node = fdt_first_subnode(fdt, node);
+	     node != -FDT_ERR_NOTFOUND;
+	     node = fdt_next_subnode(fdt, node)) {
+		const char *name;
+		int length;
+
+		/* We only care if it's always on or referenced. */
+		if (!should_enable_regulator(fdt, node))
+			continue;
+
+		name = fdt_get_name(fdt, node, &length);
+		if (!strncmp(name, "dc1sw", length)) {
+			INFO("PMIC: AXP803: Enabling DC1SW\n");
+			axp_setbits(0x12, BIT(7));
+			continue;
+		}
+	}
+}
+
 int sunxi_pmic_setup(uint16_t socid, const void *fdt)
 {
 	int ret;
@@ -148,6 +195,9 @@ int sunxi_pmic_setup(uint16_t socid, const void *fdt)
 		pmic = AXP803_RSB;
 		NOTICE("BL31: PMIC: Detected AXP803 on RSB.\n");
 
+		if (fdt)
+			setup_axp803_rails(fdt);
+
 		break;
 	default:
 		NOTICE("BL31: PMIC: No support for Allwinner %x SoC.\n", socid);