spi: omap2_mcspi PIO RX fix

Before transmission of the last word in PIO RX_ONLY mode rx+tx mode
is enabled:

	/* prevent last RX_ONLY read from triggering
	 * more word i/o: switch to rx+tx
	 */
	if (c == 0 && tx == NULL)
		mcspi_write_cs_reg(spi,
				OMAP2_MCSPI_CHCONF0, l);

But because c is decremented after the test, c will never be zero and
rx+tx will not be enabled. This breaks RX_ONLY mode PIO transfers.

Fix it by decrementing c in the beginning of the various I/O loops.
Signed-off-by: NKalle Valo <kalle.valo@nokia.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/omap2_mcspi.c

@@ -350,6 +350,7 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 		tx = xfer->tx_buf;
 
 		do {
+			c -= 1;
 			if (tx != NULL) {
 				if (mcspi_wait_for_reg_bit(chstat_reg,
 						OMAP2_MCSPI_CHSTAT_TXS) < 0) {
@@ -380,7 +381,6 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 						word_len, *(rx - 1));
 #endif
 			}
-			c -= 1;
 		} while (c);
 	} else if (word_len <= 16) {
 		u16		*rx;
@@ -389,6 +389,7 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 		rx = xfer->rx_buf;
 		tx = xfer->tx_buf;
 		do {
+			c -= 2;
 			if (tx != NULL) {
 				if (mcspi_wait_for_reg_bit(chstat_reg,
 						OMAP2_MCSPI_CHSTAT_TXS) < 0) {
@@ -419,7 +420,6 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 						word_len, *(rx - 1));
 #endif
 			}
-			c -= 2;
 		} while (c);
 	} else if (word_len <= 32) {
 		u32		*rx;
@@ -428,6 +428,7 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 		rx = xfer->rx_buf;
 		tx = xfer->tx_buf;
 		do {
+			c -= 4;
 			if (tx != NULL) {
 				if (mcspi_wait_for_reg_bit(chstat_reg,
 						OMAP2_MCSPI_CHSTAT_TXS) < 0) {
@@ -458,7 +459,6 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
 						word_len, *(rx - 1));
 #endif
 			}
-			c -= 4;
 		} while (c);
 	}