spi: Only call transfer_one() if we have buffers to transfer

Client drivers such as the ChomeOS EC driver sometimes use transfers with
no buffers and only a delay specified in order to allow a delay after the
assertion of /CS. Rather than require controller drivers handle this noop
case gracefully put checks in the core to ensure that we don't call into
the controller for such transfers.

Reported-by: Addy Ke <addy.ke@rock-chips.com>
Tested-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Mark Brown <broonie@linaro.org>

1 files changed, 26 insertions, 18 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index e0531baf2782..0edccc82ece5 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -789,27 +789,35 @@ static int spi_transfer_one_message(struct spi_master *master,
         list_for_each_entry(xfer, &msg->transfers, transfer_list) {
                 trace_spi_transfer_start(msg, xfer);
 
-                reinit_completion(&master->xfer_completion);
-
-                ret = master->transfer_one(master, msg->spi, xfer);
-                if (ret < 0) {
-                        dev_err(&msg->spi->dev,
-                                "SPI transfer failed: %d\n", ret);
-                        goto out;
-                }
+                if (xfer->tx_buf || xfer->rx_buf) {
+                        reinit_completion(&master->xfer_completion);
+
+                        ret = master->transfer_one(master, msg->spi, xfer);
+                        if (ret < 0) {
+                                dev_err(&msg->spi->dev,
+                                        "SPI transfer failed: %d\n", ret);
+                                goto out;
+                        }
 
-                if (ret > 0) {
-                        ret = 0;
-                        ms = xfer->len * 8 * 1000 / xfer->speed_hz;
-                        ms += ms + 100; /* some tolerance */
+                        if (ret > 0) {
+                                ret = 0;
+                                ms = xfer->len * 8 * 1000 / xfer->speed_hz;
+                                ms += ms + 100; /* some tolerance */
 
-                        ms = wait_for_completion_timeout(&master->xfer_completion,
-                                                         msecs_to_jiffies(ms));
-                }
+                                ms = wait_for_completion_timeout(&master->xfer_completion,
+                                                                 msecs_to_jiffies(ms));
+                        }
 
-                if (ms == 0) {
-                        dev_err(&msg->spi->dev, "SPI transfer timed out\n");
-                        msg->status = -ETIMEDOUT;
+                        if (ms == 0) {
+                                dev_err(&msg->spi->dev,
+                                        "SPI transfer timed out\n");
+                                msg->status = -ETIMEDOUT;
+                        }
+                } else {
+                        if (xfer->len)
+                                dev_err(&msg->spi->dev,
+                                        "Bufferless transfer has length %u\n",
+                                        xfer->len);
                 }
 
                 trace_spi_transfer_stop(msg, xfer);