spi_mpc83xx: turn off SPI unit while switching mode

Documentation clearly states, that mode should not be changed till
SPMODE_ENABLE bit set.  I've seen hangs w/o this patch.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
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>

drivers/spi/spi_mpc83xx.c

@@ -176,6 +176,8 @@ static void mpc83xx_spi_chipselect(struct spi_device *spi, int value)
 			regval |= SPMODE_PM(pm);
 		}
 
+		/* Turn off SPI unit prior changing mode */
+		mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode, 0);
 		mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode, regval);
 		if (mpc83xx_spi->activate_cs)
 			mpc83xx_spi->activate_cs(spi->chip_select, pol);
@@ -249,6 +251,8 @@ int mpc83xx_spi_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 	regval &= 0xff0fffff;
 	regval |= SPMODE_LEN(bits_per_word);
 
+	/* Turn off SPI unit prior changing mode */
+	mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode, 0);
 	mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode, regval);
 
 	return 0;