spi: spi-fsl-dspi: Don't access reserved fields in SPI_MCR

The SPI_MCR_PCSIS macro assumes that the controller has a number of chip
select signals equal to 6. That is not always the case, but actually is
described through the driver-specific "spi-num-chipselects" device tree
binding. LS1028A for example only has 4 chip selects.

Don't write to the upper bits of the PCSIS field, which are reserved in
the reference manual.

Fixes: 349ad66 ("spi:Add Freescale DSPI driver for Vybrid VF610 platform")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20200318001603.9650-2-olteanv@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -22,7 +22,7 @@
 
 #define SPI_MCR				0x00
 #define SPI_MCR_MASTER			BIT(31)
-#define SPI_MCR_PCSIS			(0x3F << 16)
+#define SPI_MCR_PCSIS(x)		((x) << 16)
 #define SPI_MCR_CLR_TXF			BIT(11)
 #define SPI_MCR_CLR_RXF			BIT(10)
 #define SPI_MCR_XSPI			BIT(3)
@@ -1200,7 +1200,10 @@ static const struct regmap_config dspi_xspi_regmap_config[] = {
 
 static void dspi_init(struct fsl_dspi *dspi)
 {
-	unsigned int mcr = SPI_MCR_PCSIS;
+	unsigned int mcr;
+
+	/* Set idle states for all chip select signals to high */
+	mcr = SPI_MCR_PCSIS(GENMASK(dspi->ctlr->num_chipselect - 1, 0));
 
 	if (dspi->devtype_data->trans_mode == DSPI_XSPI_MODE)
 		mcr |= SPI_MCR_XSPI;