atmel_spi: support zero length transfer

A spi transfer with zero length is not invalid.  For example, such
transfer (len == 0 && delay_usecs != 0) can be used to achieve delay
before first CLK edge after chipselect assertion.

Signed-off-by: Atsushi Nemoto <[email protected]>
Cc: Haavard Skinnemoen <[email protected]>
Cc: David Brownell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
index 1749a27be0669f71670ec38f0670e1bf537588f4..02c8e305b14fd783e3b94a71d3c8b4d9c4ed9c68 100644 (file)
--- a/drivers/spi/atmel_spi.c
+++ b/drivers/spi/atmel_spi.c
@@ -616,7 +616,7 @@ static int atmel_spi_transfer(struct spi_device *spi, struct spi_message *msg)
                return -ESHUTDOWN;
 
        list_for_each_entry(xfer, &msg->transfers, transfer_list) {
-               if (!(xfer->tx_buf || xfer->rx_buf)) {
+               if (!(xfer->tx_buf || xfer->rx_buf) && xfer->len) {
                        dev_dbg(&spi->dev, "missing rx or tx buf\n");
                        return -EINVAL;
                }