spi_mpc83xx: support loopback mode

This exposes the hardware loopback mode to drivers, primarily for testing.

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/spi_mpc83xx.c

···
 };
 
 /* 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)
···
 		/* 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;
···
 			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);
 
···
 }
 
 /* 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)
 {