ws2812-spi not sending correct data on sam0 platform

[PeeJay]

Describe the bug The ws2812-spi driver appears to have issues on the sam0 platform. I am using a custom board that is compatible with the Adafruit itsybitsy M4 express, and have connected a WS2812b strip to PA21, running the led_strip sample. The issue is that the first LED doesn't do anything, but the remaining 5 do.

I've checked the timings with a logic analyser and they are correct, however I notice that the spi bus will return to high when idle. When using the FastLed library with an Arduino sketch the data line was low at idle. In the overlay for the ESP32 there is this...

* Workaround to support WS2812 driver */
	line-idle-low;

...in the SPI dts section, but no such option exists for sam0.

Here is the relevant part from my DTS

&sercom3 {
	status = "okay";
	compatible = "atmel,sam0-spi";
	dipo = <2>;
	dopo = <3>;

	#address-cells = <1>;
	#size-cells = <0>;

	pinctrl-0 = <&sercom3_spi_default>;
	pinctrl-names = "default";

	status_rgb_led: ws2812@0 {
		compatible = "worldsemi,ws2812-spi";
		reg = <0>;
		spi-max-frequency = <WS2812C_SPI_FREQ>;

		chain-length = <6>;
		color-mapping =	<LED_COLOR_ID_GREEN>,
						<LED_COLOR_ID_RED>,
						<LED_COLOR_ID_BLUE>;
		spi-one-frame = <WS2812C_ONE_FRAME>;
		spi-zero-frame = <WS2812C_ZERO_FRAME>;
		
	};
};

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[PeeJay]

Update: After experimenting with the SPI port there doesn't seem to be any way to get it to return to LOW when the transmission is finished. Switching the pin to GPIO has around a 200ns delay both ways so that's not an option either. I think it's simply not possible to use the sam0 SPI port. sam0-i2s does not exist and ws2812-gpio is NRF only.

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