spi_nxp_lpspi: Support word size < 8

The LPSPI does support word sizes such as 6 or 7, anything as small as 2
bits. So fix the checks and the math to allow for this in the driver.

Signed-off-by: Declan Snyder <[email protected]>

Author: decsny

drivers/spi/spi_nxp_lpspi/spi_nxp_lpspi.c

@@ -279,7 +279,8 @@ static int transceive(const struct device *dev, const struct spi_config *spi_cfg
 
 	spi_context_lock(&data->ctx, asynchronous, cb, userdata, spi_cfg);
 
-	lpspi_data->word_size_bytes = SPI_WORD_SIZE_GET(spi_cfg->operation) / BITS_PER_BYTE;
+	lpspi_data->word_size_bytes =
+		DIV_ROUND_UP(SPI_WORD_SIZE_GET(spi_cfg->operation), BITS_PER_BYTE);
 	if (lpspi_data->word_size_bytes > 4) {
 		LOG_ERR("Maximum 4 byte word size");
 		ret = -EINVAL;

drivers/spi/spi_nxp_lpspi/spi_nxp_lpspi_common.c

@@ -81,7 +81,7 @@ static inline int lpspi_validate_xfer_args(const struct spi_config *spi_cfg)
 		return -ENOTSUP;
 	}
 
-	if (word_size < 8 || (word_size % 32 == 1)) {
+	if (word_size < 2 || (word_size % 32 == 1)) {
 		/* Zephyr word size == hardware FRAME size (not word size)
 		 * Max frame size: 4096 bits
 		 *   (zephyr field is 6 bit wide for max 64 bit size, no need to check)
@@ -154,7 +154,7 @@ int spi_mcux_configure(const struct device *dev, const struct spi_config *spi_cf
 
 	LPSPI_MasterGetDefaultConfig(&master_config);
 
-	master_config.bitsPerFrame = word_size;
+	master_config.bitsPerFrame = word_size < 8 ? 8 : word_size; /* minimum FRAMSZ is 8 */
 	master_config.cpol = (SPI_MODE_GET(spi_cfg->operation) & SPI_MODE_CPOL)
 				     ? kLPSPI_ClockPolarityActiveLow
 				     : kLPSPI_ClockPolarityActiveHigh;