asoc : snd_soc_simple_card connection to AKM4556 codec (i2s) issue on arm64

[Markus Bollinger <markus.bollinger@xxxxxxxxxxx>]

Hello,

I try to get working an AKM4556 codec on the arm64 Rockchip RK3399 board 
under Linux 4.4.179
The codec is a simple one (without i2c connection), similar to AKM4554 
(but 24 bit instead of 16 bit audio) and hard configured to use i2s.
I implemented the driver soc/codecs/ak4556.c which has only few 
differences to ak4554.c.
But when I try to get it working with the soc/general/simple-card.c, the 
connection to the codec fails
Both drivers (snd_soc_simple_card and snd_soc_ak4556) get loaded, the 
call to

asoc_simple_card_dai_link_of -> asoc_simple_card_sub_parse_of(cpu, ..)

is OK, but the call to

asoc_simple_card_dai_link_of -> asoc_simple_card_sub_parse_of(codec, ..) 
-> snd_soc_of_get_dai_name

fails with -EPROBE_DEFER.

Now, i am not sure if it is a driver issue or rather a device-tree one. 
I declared dt like this :

/ {

    ak4556_card: ak4556-adc-dac {
        status = "okay";
        compatible = "simple-audio-card";

        simple-audio-card,name = "ak4556";
        simple-audio-card,format = "i2s";
        simple-audio-card,mclk-fs = <256>;

        simple-audio-card,widgets =
            "Line", "Line In",
            "Line", "Line Out";
        simple-audio-card,routing =
            "LIN", "Line In",
            "RIN", "Line In",
            "Line Out", "LOUT",
            "Line Out", "ROUT";

        simple-audio-card,cpu {
            sound-dai = <&i2s0>;
        };
        simple-audio-card,codec {
            sound-dai = <&ak4556_codec>;
        };
    };

    ak4556_codec: ak4556-codec {
        status = "okay";
        compatible = "asahi-kasei,ak4556";
        #sound-dai-cells = <0>;
    };

    i2s0: i2s@ff880000 {

        compatible = "rockchip,rk3399-i2s", "rockchip,rk3066-i2s";
        reg = <0x0 0xff880000 0x0 0x1000>;
        rockchip,grf = <&grf>;
        interrupts = <GIC_SPI 39 IRQ_TYPE_LEVEL_HIGH 0>;
        dmas = <&dmac_bus 0>, <&dmac_bus 1>;
        dma-names = "tx", "rx";
        clock-names = "i2s_clk", "i2s_hclk";
        clocks = <&cru SCLK_I2S0_8CH>, <&cru HCLK_I2S0_8CH>;
        resets = <&cru SRST_I2S0_8CH>, <&cru SRST_H_I2S0_8CH>;
        reset-names = "reset-m", "reset-h";
        pinctrl-names = "default";
        pinctrl-0 = <&i2s0_8ch_bus>;
        power-domains = <&power RK3399_PD_SDIOAUDIO>;
        status = "disabled";
    };

&i2s0 {
    #sound-dai-cells = <0>;
    assigned-clocks = <&cru SCLK_I2S0_DIV>;
    assigned-clock-parents = <&cru PLL_GPLL>;
    status = "okay";
};

Thank you in advance for your suggestions,

Markus