[nrf fromlist] drivers: spi: nrfx_spim: patch flow so bus inits before cs is set

The current flow sets CS before the SPIM peripheral actually drives
the bus. This can cause SCK to be in the incorrect initial state
dictated by CPOL. New flow enables SPIM after it has been configured,
before CS is set, and disabled is after CS is cleared, thus the bus
is driven by SPIM during the entire transfer.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>

Upstream PR #: 107414

Author: bjarki-andreasen

drivers/spi/spi_nrfx_spim_common.c

@@ -50,35 +50,41 @@ void spi_nrfx_spim_common_cs_set(const struct device *dev, const struct spi_conf
 	struct spi_nrfx_common_data *dev_data = dev->data;
 	NRF_SPIM_Type *spim_reg = dev_data->spim.p_reg;
 
-	if (spi_cfg->cs.cs_is_gpio == false && NRF_SPIM_IS_320MHZ_SPIM(spim_reg) == false) {
-		return;
-	}
+	/*
+	 * Enable the SPIM peripheral so it drives the SPI bus, ensuring correct initial bus state
+	 * before transfer starts, and setting CS if its controlled by the SPIM peripheral.
+	 */
+	nrfy_spim_enable(spim_reg);
 
 	if (spi_cfg->cs.cs_is_gpio) {
 		gpio_pin_set_dt(&spi_cfg->cs.gpio, 1);
-	} else {
-		nrfy_spim_enable(spim_reg);
 	}
 
-	k_busy_wait(spi_cfg->cs.delay);
+	/* Wait only if we control the CS pin */
+	if (spi_cfg->cs.cs_is_gpio || NRF_SPIM_IS_320MHZ_SPIM(spim_reg)) {
+		k_busy_wait(spi_cfg->cs.delay);
+	}
 }
 
 void spi_nrfx_spim_common_cs_clear(const struct device *dev, const struct spi_config *spi_cfg)
 {
 	struct spi_nrfx_common_data *dev_data = dev->data;
 	NRF_SPIM_Type *spim_reg = dev_data->spim.p_reg;
 
-	if (spi_cfg->cs.cs_is_gpio == false && NRF_SPIM_IS_320MHZ_SPIM(spim_reg) == false) {
-		return;
+	/* Wait only if we control the CS pin */
+	if (spi_cfg->cs.cs_is_gpio || NRF_SPIM_IS_320MHZ_SPIM(spim_reg)) {
+		k_busy_wait(spi_cfg->cs.delay);
 	}
 
-	k_busy_wait(spi_cfg->cs.delay);
-
 	if (spi_cfg->cs.cs_is_gpio) {
 		gpio_pin_set_dt(&spi_cfg->cs.gpio, 0);
-	} else {
-		nrfy_spim_disable(spim_reg);
 	}
+
+	/*
+	 * Disable the SPIM peripheral so it no longer drives the SPI bus, clearing CS if its
+	 * controlled by the SPIM peripheral.
+	 */
+	nrfy_spim_disable(spim_reg);
 }
 
 static void evt_handler(nrfx_spim_event_t const *evt, void *data)