Hard fault in spi_nrfx_spim.c>configure when writing to a SPIM interface without a CLK defined

[gjea]

Test platform: nRF54L15-DK

NRF Connect 2.9.0

When calling spi_write_dt, under the hood spi_nrfx_spim.c > configure is called to prepare the SPIM interface for a transmission.

The following line in spi_nrfx_spim.c > configure produces a hard fault:

	nrfy_gpio_pin_write(nrfy_spim_sck_pin_get(dev_config->spim.p_reg),
			    spi_cfg->operation & SPI_MODE_CPOL ? 1 : 0);

nrfy_spim_sck_pin_get queries the harware SPIM device for the CLK pin.

If no CLK pin is configured, UINT_MAX is returned.

nrfy_gpio_pin_write sets the pin to the correct level for the pending transmission.

However, if no CLK pin is configured, nrfy_pio_pin_write will try to set pin 4294967295, which results in a fault.

Solution: Check if the CLK pin is valid before setting it.

    uint32_t sck_pin = nrfy_spim_sck_pin_get(dev_config->spim.p_reg);
	if (sck_pin != UINT_MAX) {
		nrfy_gpio_pin_write(sck_pin,
				    spi_cfg->operation & SPI_MODE_CPOL ? 1 : 0);
	}

Background:

The WS2812 LED driver uses the SPI interface for a 1 wire serial interface.

To use this 1-wire interface, only MOSI is required, the CLK pin can be left unconnected.

[gjea]

I just realized that in register PSEL.SCN bit 31 indicates if the CLK pin is disconnected.

From the NRF54L15 datasheet:

so the patch should actually be slightly modified:

	uint32_t sck_pin = nrfy_spim_sck_pin_get(dev_config->spim.p_reg);
	bool sck_pin_disconnected = sck_pin & 0x80000000;
	if (!sck_pin_disconnected) {
		nrfy_gpio_pin_write(sck_pin,
				    spi_cfg->operation & SPI_MODE_CPOL ? 1 : 0);
	}

[gjea]

Just saw that this bug was fixed:

https://github.com/zephyrproject-rtos/zephyr/commit/291a688de6df44b448e7f55e44e3d7bd95f0a64c

Thanks all!