allwinner: A64: Add AXP803 PMIC support to power off the board

Boards with the Allwinner A64 SoC are mostly paired with an AXP803 PMIC,
which allows to programmatically power down the board.

Use the newly introduced RSB driver to detect and program the PMIC on
boot, then later to turn off the main voltage rails when receiving a
PSCI SYSTEM_POWER_OFF command.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

plat/allwinner/sun50i_a64/platform.mk

@@ -6,3 +6,5 @@
 
 # The differences between the platform are covered by the include files.
 include plat/allwinner/common/allwinner-common.mk
+
+PLAT_BL_COMMON_SOURCES	+=	drivers/allwinner/sunxi_rsb.c

plat/allwinner/sun50i_a64/sunxi_power.c

@@ -5,6 +5,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
+#include <allwinner/sunxi_rsb.h>
 #include <arch_helpers.h>
 #include <debug.h>
 #include <delay_timer.h>
@@ -19,8 +20,12 @@ static enum pmic_type {
 	GENERIC_H5,
 	GENERIC_A64,
 	REF_DESIGN_H5,	/* regulators controlled by GPIO pins on port L */
+	AXP803_RSB,	/* PMIC connected via RSB on most A64 boards */
 } pmic;
 
+#define AXP803_HW_ADDR	0x3a3
+#define AXP803_RT_ADDR	0x2d
+
 /*
  * On boards without a proper PMIC we struggle to turn off the system properly.
  * Try to turn off as much off the system as we can, to reduce power
@@ -76,8 +81,55 @@ void sunxi_turn_off_soc(uint16_t socid)
 	}
 }
 
+static int rsb_init(void)
+{
+	int ret;
+
+	ret = rsb_init_controller();
+	if (ret)
+		return ret;
+
+	/* Start with 400 KHz to issue the I2C->RSB switch command. */
+	ret = rsb_set_bus_speed(SUNXI_OSC24M_CLK_IN_HZ, 400000);
+	if (ret)
+		return ret;
+
+	/*
+	 * Initiate an I2C transaction to write 0x7c into register 0x3e,
+	 * switching the PMIC to RSB mode.
+	 */
+	ret = rsb_set_device_mode(0x7c3e00);
+	if (ret)
+		return ret;
+
+	/* Now in RSB mode, switch to the recommended 3 MHz. */
+	ret = rsb_set_bus_speed(SUNXI_OSC24M_CLK_IN_HZ, 3000000);
+	if (ret)
+		return ret;
+
+	/* Associate the 8-bit runtime address with the 12-bit bus address. */
+	return rsb_assign_runtime_address(AXP803_HW_ADDR,
+					  AXP803_RT_ADDR);
+}
+
+static int axp_setbits(uint8_t reg, uint8_t set_mask)
+{
+	uint8_t regval;
+	int ret;
+
+	ret = rsb_read(AXP803_RT_ADDR, reg);
+	if (ret < 0)
+		return ret;
+
+	regval = ret | set_mask;
+
+	return rsb_write(AXP803_RT_ADDR, reg, regval);
+}
+
 int sunxi_pmic_setup(uint16_t socid)
 {
+	int ret;
+
 	switch (socid) {
 	case SUNXI_SOC_H5:
 		pmic = REF_DESIGN_H5;
@@ -85,6 +137,17 @@ int sunxi_pmic_setup(uint16_t socid)
 		break;
 	case SUNXI_SOC_A64:
 		pmic = GENERIC_A64;
+		ret = sunxi_init_platform_r_twi(socid, true);
+		if (ret)
+			return ret;
+
+		ret = rsb_init();
+		if (ret)
+			return ret;
+
+		pmic = AXP803_RSB;
+		NOTICE("BL31: PMIC: Detected AXP803 on RSB.\n");
+
 		break;
 	default:
 		NOTICE("BL31: PMIC: No support for Allwinner %x SoC.\n", socid);
@@ -126,6 +189,14 @@ void __dead2 sunxi_power_down(void)
 		/* Turn off pin controller now. */
 		mmio_write_32(SUNXI_CCU_BASE + 0x68, 0);
 
+		break;
+	case AXP803_RSB:
+		/* (Re-)init RSB in case the rich OS has disabled it. */
+		sunxi_init_platform_r_twi(SUNXI_SOC_A64, true);
+		rsb_init();
+
+		/* Set "power disable control" bit */
+		axp_setbits(0x32, BIT(7));
 		break;
 	default:
 		break;