diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
index 0274c9295514..ddfdb903047a 100644
--- a/drivers/spi/spi-dw-core.c
+++ b/drivers/spi/spi-dw-core.c
@@ -6,6 +6,7 @@
  */
 
 #include <linux/bitfield.h>
+#include <linux/bitops.h>
 #include <linux/dma-mapping.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
@@ -421,10 +422,7 @@ static int dw_spi_transfer_one(struct spi_controller *host,
 	int ret;
 
 	dws->dma_mapped = 0;
-	dws->n_bytes =
-		roundup_pow_of_two(DIV_ROUND_UP(transfer->bits_per_word,
-						BITS_PER_BYTE));
-
+	dws->n_bytes = roundup_pow_of_two(BITS_TO_BYTES(transfer->bits_per_word));
 	dws->tx = (void *)transfer->tx_buf;
 	dws->tx_len = transfer->len / dws->n_bytes;
 	dws->rx = transfer->rx_buf;
@@ -836,6 +834,20 @@ static void dw_spi_hw_init(struct device *dev, struct dw_spi *dws)
 			DW_SPI_GET_BYTE(dws->ver, 1));
 	}
 
+	/*
+	 * Try to detect the number of native chip-selects if the platform
+	 * driver didn't set it up. There can be up to 16 lines configured.
+	 */
+	if (!dws->num_cs) {
+		u32 ser;
+
+		dw_writel(dws, DW_SPI_SER, 0xffff);
+		ser = dw_readl(dws, DW_SPI_SER);
+		dw_writel(dws, DW_SPI_SER, 0);
+
+		dws->num_cs = hweight16(ser);
+	}
+
 	/*
 	 * Try to detect the FIFO depth if not set by interface driver,
 	 * the depth could be from 2 to 256 from HW spec
diff --git a/drivers/spi/spi-dw-mmio.c b/drivers/spi/spi-dw-mmio.c
index cc74cbe03431..c56de35eca98 100644
--- a/drivers/spi/spi-dw-mmio.c
+++ b/drivers/spi/spi-dw-mmio.c
@@ -320,7 +320,6 @@ static int dw_spi_mmio_probe(struct platform_device *pdev)
 	struct resource *mem;
 	struct dw_spi *dws;
 	int ret;
-	int num_cs;
 
 	dwsmmio = devm_kzalloc(&pdev->dev, sizeof(struct dw_spi_mmio),
 			GFP_KERNEL);
@@ -364,11 +363,8 @@ static int dw_spi_mmio_probe(struct platform_device *pdev)
 				     &dws->reg_io_width))
 		dws->reg_io_width = 4;
 
-	num_cs = 4;
-
-	device_property_read_u32(&pdev->dev, "num-cs", &num_cs);
-
-	dws->num_cs = num_cs;
+	/* Rely on the auto-detection if no property specified */
+	device_property_read_u32(&pdev->dev, "num-cs", &dws->num_cs);
 
 	init_func = device_get_match_data(&pdev->dev);
 	if (init_func) {
diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 6cafeee8ee2a..fc267c6437ae 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h
@@ -164,8 +164,8 @@ struct dw_spi {
 	u32			max_freq;	/* max bus freq supported */
 
 	u32			reg_io_width;	/* DR I/O width in bytes */
+	u32			num_cs;		/* chip select lines */
 	u16			bus_num;
-	u16			num_cs;		/* supported slave numbers */
 	void (*set_cs)(struct spi_device *spi, bool enable);
 
 	/* Current message transfer state info */