spidev supports more communications modes

The spidev driver doesn't currently expose all SPI communications modes to
userspace. This passes them all through to the driver.

Two of them are potentially troublesome, in the sense that they could cause
hardware conflicts on shared busses. It might be appropriate to add some
privilege checks for for those modes.

Signed-off-by: Anton Vorontsov <[e-mail]>
Signed-off-by: David Brownell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/spi/spidev.c

···
 static unsigned long	minors[N_SPI_MINORS / BITS_PER_LONG];
 
 
-/* Bit masks for spi_device.mode management */
-#define SPI_MODE_MASK			(SPI_CPHA | SPI_CPOL)
-
+/* Bit masks for spi_device.mode management.  Note that incorrect
+ * settings for CS_HIGH and 3WIRE can cause *lots* of trouble for other
+ * devices on a shared bus:  CS_HIGH, because this device will be
+ * active when it shouldn't be;  3WIRE, because when active it won't
+ * behave as it should.
+ *
+ * REVISIT should changing those two modes be privileged?
+ */
+#define SPI_MODE_MASK		(SPI_CPHA | SPI_CPOL | SPI_CS_HIGH \
+				| SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP)
 
 struct spidev_data {
 	struct device		dev;

include/linux/spi/spidev.h

···
 #define SPI_MODE_2		(SPI_CPOL|0)
 #define SPI_MODE_3		(SPI_CPOL|SPI_CPHA)
 
+#define SPI_CS_HIGH		0x04
+#define SPI_LSB_FIRST		0x08
+#define SPI_3WIRE		0x10
+#define SPI_LOOP		0x20
 
 /*---------------------------------------------------------------------------*/