allwinner: rsb: Set the PMIC to RSB mode

With recent ATF (v2.5) the PMIC is reset to I2C mode.
Without a PMIC no regulators can be changed/enabled/disabled
This fixes cpufreq on A64 (at least) and anything else that needs
regulators handled by the PMIC.

MFC after:	3 days
Sponsored by:	Diablotin Systems

sys/arm/allwinner/aw_rsb.c

@@ -71,6 +71,10 @@ __FBSDID("$FreeBSD$");
 #define	 DLEN_READ		(1 << 4)
 #define	RSB_DATA0		0x1c
 #define	RSB_DATA1		0x20
+#define	RSB_PMCR		0x28
+#define	 RSB_PMCR_START		(1 << 31)
+#define	 RSB_PMCR_DATA(x)	(x << 16)
+#define	 RSB_PMCR_REG(x)	(x << 8)
 #define	RSB_CMD			0x2c
 #define	 CMD_SRTA		0xe8
 #define	 CMD_RD8		0x8b
@@ -93,6 +97,10 @@ __FBSDID("$FreeBSD$");
 #define	RSB_ADDR_PMIC_SECONDARY	0x745
 #define	RSB_ADDR_PERIPH_IC	0xe89
 
+#define	PMIC_MODE_REG	0x3e
+#define	PMIC_MODE_I2C	0x00
+#define	PMIC_MODE_RSB	0x7c
+
 #define	A31_P2WI	1
 #define	A23_RSB		2
 
@@ -436,6 +444,9 @@ rsb_attach(device_t dev)
 		goto fail;
 	}
 
+	/* Set the PMIC into RSB mode as ATF might have leave it in I2C mode */
+	RSB_WRITE(sc, RSB_PMCR, RSB_PMCR_REG(PMIC_MODE_REG) | RSB_PMCR_DATA(PMIC_MODE_RSB) | RSB_PMCR_START);
+
 	sc->iicbus = device_add_child(dev, "iicbus", -1);
 	if (sc->iicbus == NULL) {
 		device_printf(dev, "cannot add iicbus child device\n");