The AXP20X chips have a configuration register "REG 30H: VBUS-IPSOUT Power 
Path Management" that provide USB power supply protection.
The current axp20x_usb_power.c provides support only for reading those 
values.

>From the datasheet:
In order not to affect the USB communication, VBUS is always working under 
Voltage-Limit mode by default. In this mode, AXP209 ensures that VBUS 
voltage remains above a configurable reference voltage VHOLD which can meet 
the USB specification. The default VHOLD is 4.4V, adjustable in Reg30H 
[5:3] register. If the system has limit on current obtained from USB VBUS, 
a current-limit mode is provided (See REG30H[1] register), with 
900mA/500mA/100mA (Reg30H [0]) selectable.

The following entries are added in the axp209.dtsi 
file: vhold-enable, vhold-set and ibus-limit
The chosen default values are the AXP20X reset values, as described in the 
data sheet.

Signed-off-by: Ene Alexandru <ene.alexan...@gmail.com>


---
diff -uprN -X linux-sunxi-original/Documentation/dontdiff 
linux-sunxi-original/arch/arm/boot/dts/axp209.dtsi 
linux-sunxi/arch/arm/boot/dts/axp209.dtsi
--- linux-sunxi-original/arch/arm/boot/dts/axp209.dtsi         2016-05-11 
09:21:47.470923679 +0200
+++ linux-sunxi/arch/arm/boot/dts/axp209.dtsi     2016-05-10 
18:45:32.795158651 +0200
@@ -98,5 +98,8 @@
           usb_power_supply: usb_power_supply {
                       compatible = "x-powers,axp202-usb-power-supply";
                       status = "disabled";
+                      vhold-enable = <0x01>;
+                      vhold-set = <0x04>;
+                      ibus-limit = <0x01>;
           };
};
---

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