SPI word size in Zephyr

Question

I'm using Zephyr with SDK v2.3.0.

I'm using the Laird BL652 BLE module (with the nRF52832) on my board, which comes with a nice device tree that includes a setup for spi0:

&spi0 {
	compatible = "nordic,nrf-spi";
	/* Cannot be used together with i2c0. */
	/* status = "okay"; */
	cs-gpios = <&gpio0 22 GPIO_ACTIVE_LOW>;
	pinctrl-0 = <&spi0_default>;
	pinctrl-1 = <&spi0_sleep>;
	pinctrl-names = "default", "sleep";
};

I've added an overlay that moves the CS GPIO to number 18, which is what my board uses:

&spi0 {
    cs-gpios = <&gpio0 18 GPIO_ACTIVE_LOW>;
    status = "okay";
};

However, the slave I want to talk to needs a 16-bit word size and I can't understand where to set that in the device tree or at run-time. Maybe the default is 16-bit, but I can't find where that's specified either.

Regards,

Bret

Bret Foreman · Accepted Answer

Update: 
 I found that I can put multiple bytes into the spi_buf_set/spi_buf structs but it's not clear from those structures what word size will be used. Maybe having two bytes in the buffer will cause the SPI hardware to do two separate transactions.

SPI word size in Zephyr

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