serial: 8250_dma: TX optimisation

Remove one useless wakeup, and do not use DMA with zero byte
transfers.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 02333fc17f411514c115f89e87da357635c8cba1..b9f7fd28112e3aba78a4f595520769baf8e538d4 100644 (file)
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -67,12 +67,12 @@ int serial8250_tx_dma(struct uart_8250_port *p)
        struct circ_buf                 *xmit = &p->port.state->xmit;
        struct dma_async_tx_descriptor  *desc;
 
-       if (dma->tx_running) {
-               uart_write_wakeup(&p->port);
+       if (dma->tx_running)
                return -EBUSY;
-       }
 
        dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
+       if (!dma->tx_size)
+               return -EINVAL;
 
        desc = dmaengine_prep_slave_single(dma->txchan,
                                           dma->tx_addr + xmit->tail,