spi_nxp_lpspi: Add maximum wait time of fifo empty

Instead of waiting forever and potentially allowing infinite loop on
ISR, wait some arbitrary amount of cycles to error out if it isn't
happening. Still make this configurable for debugging purposes.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>

Author: decsny

drivers/spi/spi_nxp_lpspi/Kconfig

@@ -36,4 +36,20 @@ config SPI_MCUX_LPSPI_CPU
 	  This has lower latency than DMA-based driver but over the
 	  longer transfers will likely have less bandwidth and use more CPU time.
 
+config SPI_NXP_LPSPI_TXFIFO_WAIT_CYCLES
+	int "Number of CPU cycles to wait on TX fifo empty"
+	default 0 if DEBUG
+	default 10000
+	help
+	  This option most likely does not need changed.
+	  The drivers tend to need to wait on confirming the transmit command
+	  is consumed by the hardware by checking of the TX fifo is emptied.
+	  Usually this should not be a problem and should happen immediately,
+	  but in the rare case of some bug, this option is available to avoid
+	  infinite loop locking the system in ISR. So this option gives a maximum
+	  number of CPU cycles to wait on that. The special value of 0 means infinite.
+	  The default of 10000 is arbitrary. The default of 0 if DEBUG is enabled
+	  is because getting stuck on that infinite loop can be useful for debugging
+	  the rare case of why the hardware is not consuming a command during development.
+
 endif # SPI_MCUX_LPSPI

drivers/spi/spi_nxp_lpspi/spi_nxp_lpspi.c

@@ -335,7 +335,10 @@ static int transceive(const struct device *dev, const struct spi_config *spi_cfg
 		base->TCR |= LPSPI_TCR_CONT_MASK;
 	}
 	/* tcr is written to tx fifo */
-	lpspi_wait_tx_fifo_empty(dev);
+	ret = lpspi_wait_tx_fifo_empty(dev);
+	if (ret) {
+		return ret;
+	}
 
 	/* start the transfer sequence which are handled by irqs */
 	lpspi_next_tx_fill(dev);

drivers/spi/spi_nxp_lpspi/spi_nxp_lpspi_common.c

@@ -60,12 +60,20 @@ static inline clock_ip_name_t lpspi_get_clock(LPSPI_Type *const base)
 }
 #endif
 
-void lpspi_wait_tx_fifo_empty(const struct device *dev)
+int lpspi_wait_tx_fifo_empty(const struct device *dev)
 {
 	LPSPI_Type *base = (LPSPI_Type *)DEVICE_MMIO_NAMED_GET(dev, reg_base);
+	int arbitrary_cycle_limit = CONFIG_SPI_NXP_LPSPI_TXFIFO_WAIT_CYCLES;
+	bool limit_wait = arbitrary_cycle_limit > 0;
 
-	while (LPSPI_GetTxFifoCount(base) != 0) {
+	while (FIELD_GET(LPSPI_FSR_TXCOUNT_MASK, base->FSR) != 0) {
+		if (limit_wait && (arbitrary_cycle_limit-- < 0)) {
+			LOG_WRN("Failed waiting for TX fifo empty");
+			return -EIO;
+		}
 	}
+
+	return 0;
 }
 
 int spi_lpspi_release(const struct device *dev, const struct spi_config *spi_cfg)

drivers/spi/spi_nxp_lpspi/spi_nxp_lpspi_priv.h

@@ -68,7 +68,7 @@ int spi_nxp_init_common(const struct device *dev);
 /* common api function for now */
 int spi_lpspi_release(const struct device *dev, const struct spi_config *spi_cfg);
 
-void lpspi_wait_tx_fifo_empty(const struct device *dev);
+int lpspi_wait_tx_fifo_empty(const struct device *dev);
 
 #define SPI_LPSPI_IRQ_FUNC_LP_FLEXCOMM(n)                                                     \
 	nxp_lp_flexcomm_setirqhandler(DEVICE_DT_GET(DT_INST_PARENT(n)), DEVICE_DT_INST_GET(n),     \