atmel-hlcdc-dc: failed to create HLCDC outputs: -517

[oohay0000]

I have a custom board using SAMA5D27 processor driving an AUO g121sn01 LCD display. The LCD driver fails to initialize whenever the back light node is included in the panel node, no matter I use a GPIO back light or a PWM back light configuration. The LCD controller works fine if I commented out the backlight node and turn on the GPIO through the /sys interface. The kernel error message and device tree nodes as following,

backlight: backlight {
compatible = "gpio-backlight";
gpios = <&pioA PIN_PC3 GPIO_ACTIVE_HIGH>;
default-on;
status = "okay";
};

panel: panel {
compatible = "auo,g121sn01v4", "simple-panel";
backlight = <&backlight>;
power-supply = <&panel_reg>;
#address-cells = <1>;
#size-cells = <0>;
status = "okay";

port@0 {
reg = <0>;
#address-cells = <1>;
#size-cells = <0>;

panel_input: endpoint@0 {
remote-endpoint = <&hlcdc_panel_output>;
};
};
};


[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] No driver support for vblank timestamp query.
atmel-hlcdc-display-controller atmel-hlcdc-dc: failed to create HLCDC outputs: -517
atmel-hlcdc-display-controller atmel-hlcdc-dc: failed to initialize mode setting

There is a discussion thread similar to my situation but the code modification doesn't seem to work for me, viewtopic.php?t=25251.

Thank you very much in advance.