diff --git a/drivers/hwmon/lm70.c b/drivers/hwmon/lm70.c
index 7eaae3834e1..275d392eca6 100644
--- a/drivers/hwmon/lm70.c
+++ b/drivers/hwmon/lm70.c
@@ -96,6 +96,10 @@ static int __devinit lm70_probe(struct spi_device *spi)
 	struct lm70 *p_lm70;
 	int status;
 
+	/* signaling is SPI_MODE_0 on a 3-wire link (shared SI/SO) */
+	if ((spi->mode & (SPI_CPOL|SPI_CPHA)) || !(spi->mode & SPI_3WIRE))
+		return -EINVAL;
+
 	p_lm70 = kzalloc(sizeof *p_lm70, GFP_KERNEL);
 	if (!p_lm70)
 		return -ENOMEM;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 1be5ea05947..302b81d1d11 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -76,6 +76,7 @@ struct spi_device {
 #define	SPI_MODE_3	(SPI_CPOL|SPI_CPHA)
 #define	SPI_CS_HIGH	0x04			/* chipselect active high? */
 #define	SPI_LSB_FIRST	0x08			/* per-word bits-on-wire */
+#define	SPI_3WIRE	0x10			/* SI/SO signals shared */
 	u8			bits_per_word;
 	int			irq;
 	void			*controller_state;