spi: simplify spi_write_then_read()

Modify spi_write_then_read() to use one transfer.  This speeds up all
callers, and is a minor code shrink.

Signed-off-by: Vernon Sauder <Vernon.Sauder@gmail.com>
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>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 75e86865234c924a67bb94d39c3fc259a6925b5a..2de6b0e72f3f82a26446ec13bf3cc55772b10a7e 100644 (file)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -660,7 +660,7 @@ int spi_write_then_read(struct spi_device *spi,
 
        int                     status;
        struct spi_message      message;
-       struct spi_transfer     x[2];
+       struct spi_transfer     x;
        u8                      *local_buf;
 
        /* Use preallocated DMA-safe buffer.  We can't avoid copying here,
@@ -671,15 +671,9 @@ int spi_write_then_read(struct spi_device *spi,
                return -EINVAL;
 
        spi_message_init(&message);
-       memset(x, 0, sizeof x);
-       if (n_tx) {
-               x[0].len = n_tx;
-               spi_message_add_tail(&x[0], &message);
-       }
-       if (n_rx) {
-               x[1].len = n_rx;
-               spi_message_add_tail(&x[1], &message);
-       }
+       memset(&x, 0, sizeof x);
+       x.len = n_tx + n_rx;
+       spi_message_add_tail(&x, &message);
 
        /* ... unless someone else is using the pre-allocated buffer */
        if (!mutex_trylock(&lock)) {
@@ -690,15 +684,15 @@ int spi_write_then_read(struct spi_device *spi,
                local_buf = buf;
 
        memcpy(local_buf, txbuf, n_tx);
-       x[0].tx_buf = local_buf;
-       x[1].rx_buf = local_buf + n_tx;
+       x.tx_buf = local_buf;
+       x.rx_buf = local_buf;
 
        /* do the i/o */
        status = spi_sync(spi, &message);
        if (status == 0)
-               memcpy(rxbuf, x[1].rx_buf, n_rx);
+               memcpy(rxbuf, x.rx_buf + n_tx, n_rx);
 
-       if (x[0].tx_buf == buf)
+       if (x.tx_buf == buf)
                mutex_unlock(&lock);
        else
                kfree(local_buf);