[SEEED][XIAO_BLE] QSPI Doesn't Use All SPI I/O Lines

[MaprilBear]

Hiya! Popping in to share something I've noticed with the current device tree for the xiao_ble board.

Right now, the qspi node has an instance of the nordic qspi-nor driver that is set up to work with the on-board p25q16h flash chip. The driver has the quad-enable-requirements property to enable QSPI communication with the chip, but it fails to specify the readoc and writeoc properties to actually use Quad I/O reading/writing. The defaults result in only a single line used for I/O.

I've tested setting them to read4io and pp4io and they work on my XIAO nRF52840 as expected.

The PR that introduced the quad-enable-requirements property (#55199) did not mention readoc or writeoc at all. The PR that initially introduced the board (#46358) experimented with QSPI at first and folks in the comments did use the readoc/writeoc properties (#46358 (comment) #46358 (comment)). However after some issues arose, adding QSPI was deferred and eventually tackled by the PR I mentioned previously.

Are the readoc/writeoc properties an intentional omission or should this be an improvement?

zephyr/boards/seeed/xiao_ble/xiao_ble_common.dtsi

Lines 123 to 136 in 497209c

	p25q16h: p25q16h@0 {
	compatible = "nordic,qspi-nor";
	reg = <0>;
	sck-frequency = <104000000>;
	quad-enable-requirements = "S2B1v1";
	jedec-id = [85 60 15];
	sfdp-bfp = [e5 20 f1 ff ff ff ff 00 44 eb 08 6b 08 3b 80 bb
	ee ff ff ff ff ff 00 ff ff ff 00 ff 0c 20 0f 52
	10 d8 08 81];
	size = <16777216>;
	has-dpd;
	t-enter-dpd = <3000>;
	t-exit-dpd = <8000>;
	};

nordic,qspi-nor driver docs: https://docs.zephyrproject.org/latest/build/dts/api/bindings/mtd/nordic,qspi-nor.html#nordic-qspi-nor-on-qspi-bus