Cannot configure SPI0 on BeagleBone Green Wireless

Note: the selected answer is the original one that solved the problem, for more details refer to the additional one below.

I'm not able to configure SPI0 on my BeagleBone Green Wireless (BBGW). I'm trying to achieve this without using overlays, only pure DeviceTree.

/dev/spidev1.0 and /dev/spidev1.1 are there, but any I/O returns garbage.

Oscilloscope connected to SCLK displays mostly noise, here are pictures (each in different time scale).

Important parts of my .dts/.dtsi:

&am33xx_pinmux {
    bb_spi0_pins: pinmux_bb_spi0_pins {
        pinctrl-single,pins = <
            BONE_P9_22 ( PIN_INPUT_PULLUP | MUX_MODE0 ) // SCLK
            BONE_P9_21 ( PIN_INPUT_PULLUP | MUX_MODE0 ) // MISO
            BONE_P9_18 ( PIN_OUTPUT_PULLUP | MUX_MODE0 ) // MOSI
            BONE_P9_17 ( PIN_OUTPUT_PULLUP | MUX_MODE0 ) // CS0
        >;
    };
};

&spi0 {
    status = "okay";
    pinctrl-names = "default";
    pinctrl-0 = <&bb_spi0_pins>;
    #address-cells = <1>;
    #size-cells = <0>;

    channel@0 {
        #address-cells = <1>;
        #size-cells = <0>;
        compatible = "linux,spidev";
        spi-max-frequency = <16000000>;
        reg = <0>;
    };

    channel@1 {
        #address-cells = <1>;
        #size-cells = <0>;
        compatible = "linux,spidev";
        spi-max-frequency = <16000000>;
        reg = <1>;
    };
};

More info:

I didn't use the available am335x-bone-pinmux-spi0.dtsi as it enables the clock phase shift (spi-cpha)
I'm intending to use the SPI to communicate with a DWM1000
I'm using a custom cape with the said DWM1000, a power converter and 2 motor drivers connected to PRU pins on P8 connector
Full overlay files: https://github.com/GroupOfRobots/RobotConfig/tree/v3/DevTree
uEnv.txt: https://github.com/GroupOfRobots/RobotConfig/blob/v3/uEnv.txt
system: Debian 9.0 (testing)
kernel: 4.4.80-ti-rt-r116 (I've tried on different ones too, but I need one of the ti-rt branch)

PS. I know it's BBGW not BBB but there are no tags for BBG/BBGW (yet).

Update:

The behaviour was verified to be the same on other kernels, namely:

4.4.85-armv7-x14
4.4.84-ti-r120
4.4.85-bone19

Additionally I've connected together MISO and MOSI (pins 18 and 21 on P9) with a jumper wire and ran spidev_test, here are the results:

$ sudo ./spidev_test -v -p "abcdefghijklmnopqrstuvwxyz1234\xde\xad" 
spi mode: 0x0
bits per word: 8
max speed: 500000 Hz (500 KHz)
TX | 61 62 63 64 65 66 67 68 69 6A 6B 6C 6D 6E 6F 70 71 72 73 74 75 76 77 78 79 7A 31 32 33 34 DE AD  | abcdefghijklmnopqrstuvwxyz1234ޭ
RX | 03 0C 0F 30 33 3C 3F C0 C3 CC CF F0 F3 FC FF 00 03 0C 0F 30 33 3C 3F C0 C3 CC 03 0C 0F 30 FC F3  | ...03<?�������.....03<?���...0��

I can't make anything out of it, but it makes me almost sure it's not due to the capacitors on clock line, which is unused in this test.

Solution

I had the same problem, i was using adafruit-spi0 overlays and i couldn't get it working. I was able to send the data on a slave spi device and the recieved data was ok, but when the second device sends the data back to my BBGW i was not getting the values that i have sent.

This is how i solved this, there are two capacitors 100pf on the spi0 clk they are causing reflections resulting in double-clocked data, you need to remove them.

My board was oredered from seeed studio.