[U-Boot] [PATCH] mx28: fix i.MX28 spi driver

[Matthias Fuchs <matthias.fuchs@esd.eu>]

The generic spi flash driver (drivers/mtd/spi/spi_flash.c) uses the
spi low level driver's spi_xfer() function with len=0 to deassert the
SPI flash' chip select. But the i.MX28 spi driver rejects this call
due to len=0.

This patch implements an exception for len=0 with the SPI_XFER_END
flag set. This results in an extra read with the chip select being
deasserted afterwards. There seems to be no way to deassert the signal
by hand.

Signed-off-by: Matthias Fuchs <matthias.fuchs@esd.eu>
---
 drivers/spi/mxs_spi.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/mxs_spi.c b/drivers/spi/mxs_spi.c
index 4c27fef..adb9ca8 100644
--- a/drivers/spi/mxs_spi.c
+++ b/drivers/spi/mxs_spi.c
@@ -129,9 +129,15 @@ int spi_xfer(struct spi_slave *slave, unsigned int bitlen,
 	int len = bitlen / 8;
 	const char *tx = dout;
 	char *rx = din;
-
-	if (bitlen == 0)
-		return 0;
+	char dummy;
+
+	if (bitlen == 0) {
+		if (flags & SPI_XFER_END) {
+			rx = &dummy;
+			len = 1;
+		} else
+			return 0;
+	}
 
 	if (!rx && !tx)
 		return 0;