mfd: axp20x: Add support for dts property "xpowers,master-mode"

commit b101829a029a ("mfd: axp20x: Fix AXP806 access errors on cold boot")
was intended to fix the case where a board uses an AXP806 in slave mode,
but the boot loader leaves it in master mode for lack of AXP806 support.
But now the driver breaks on boards where the PMIC is operating in master
mode. This patch lets the driver use the new device tree property
"xpowers,master-mode" to set the correct operating mode for the board.

Fixes: 8824ee85 ("mfd: axp20x: Add support for AXP806 PMIC")
Signed-off-by: Rask Ingemann Lambertsen <rask@formelder.dk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/axp20x.c

@@ -31,6 +31,7 @@
 
 #define AXP20X_OFF	0x80
 
+#define AXP806_REG_ADDR_EXT_ADDR_MASTER_MODE	0
 #define AXP806_REG_ADDR_EXT_ADDR_SLAVE_MODE	BIT(4)
 
 static const char * const axp20x_model_names[] = {
@@ -877,15 +878,19 @@ int axp20x_device_probe(struct axp20x_dev *axp20x)
 	 * the these device addressing bits (in the upper 4 bits of the
 	 * registers) match.
 	 *
-	 * Since we only support an AXP806 chained to an AXP809 in slave
-	 * mode, and there isn't any existing hardware which uses AXP806
-	 * in master mode, or has 2 AXP806s in the same system, we can
-	 * just program the register address extension to the slave mode
-	 * address.
+	 * By default we support an AXP806 chained to an AXP809 in slave
+	 * mode. Boards which use an AXP806 in master mode can set the
+	 * property "x-powers,master-mode" to override the default.
 	 */
-	if (axp20x->variant == AXP806_ID)
+	if (axp20x->variant == AXP806_ID) {
+		if (of_property_read_bool(axp20x->dev->of_node,
+					  "x-powers,master-mode"))
+			regmap_write(axp20x->regmap, AXP806_REG_ADDR_EXT,
+				     AXP806_REG_ADDR_EXT_ADDR_MASTER_MODE);
+		else
 			regmap_write(axp20x->regmap, AXP806_REG_ADDR_EXT,
 				     AXP806_REG_ADDR_EXT_ADDR_SLAVE_MODE);
+	}
 
 	ret = regmap_add_irq_chip(axp20x->regmap, axp20x->irq,
 			  IRQF_ONESHOT | IRQF_SHARED | axp20x->irq_flags,