SPI: add 3wire mode flag

Add a new spi->mode bit: SPI_3WIRE, for chips where the SI and SO signals
are shared (and which are thus only half duplex).  Update the LM70 driver
to require support for that hardware mode from the controller.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 5 insertions, 0 deletions

diff --git a/drivers/hwmon/lm70.c b/drivers/hwmon/lm70.c
index 7eaae3834e15..275d392eca61 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 1be5ea059477..302b81d1d117 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;