spi_mpc83xx: support loopback mode

This exposes the hardware loopback mode to drivers, primarily for testing.
Signed-off-by: NAnton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/spi/spi_mpc83xx.c

@@ -39,6 +39,7 @@ struct mpc83xx_spi_reg {
 };
 
 /* SPI Controller mode register definitions */
+#define	SPMODE_LOOP		(1 << 30)
 #define	SPMODE_CI_INACTIVEHIGH	(1 << 29)
 #define	SPMODE_CP_BEGIN_EDGECLK	(1 << 28)
 #define	SPMODE_DIV16		(1 << 27)
@@ -155,7 +156,7 @@ static void mpc83xx_spi_chipselect(struct spi_device *spi, int value)
 		/* mask out bits we are going to set */
 		regval &= ~(SPMODE_CP_BEGIN_EDGECLK | SPMODE_CI_INACTIVEHIGH
 				| SPMODE_LEN(0xF) | SPMODE_DIV16
-				| SPMODE_PM(0xF) | SPMODE_REV);
+				| SPMODE_PM(0xF) | SPMODE_REV | SPMODE_LOOP);
 
 		if (spi->mode & SPI_CPHA)
 			regval |= SPMODE_CP_BEGIN_EDGECLK;
@@ -163,6 +164,8 @@ static void mpc83xx_spi_chipselect(struct spi_device *spi, int value)
 			regval |= SPMODE_CI_INACTIVEHIGH;
 		if (!(spi->mode & SPI_LSB_FIRST))
 			regval |= SPMODE_REV;
+		if (spi->mode & SPI_LOOP)
+			regval |= SPMODE_LOOP;
 
 		regval |= SPMODE_LEN(len);
 
@@ -273,7 +276,8 @@ int mpc83xx_spi_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 }
 
 /* the spi->mode bits understood by this driver: */
-#define MODEBITS (SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_LSB_FIRST)
+#define MODEBITS	(SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \
+			| SPI_LSB_FIRST | SPI_LOOP)
 
 static int mpc83xx_spi_setup(struct spi_device *spi)
 {