1 files changed, 15 insertions, 7 deletions

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index abc705716aa0..d4504daff992 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1398,6 +1398,7 @@ static void sci_dma_tx_work_fn(struct work_struct *work)
 	struct circ_buf *xmit = &port->state->xmit;
 	unsigned long flags;
 	dma_addr_t buf;
+	int head, tail;
 
 	/*
 	 * DMA is idle now.
@@ -1407,16 +1408,23 @@ static void sci_dma_tx_work_fn(struct work_struct *work)
 	 * consistent xmit buffer state.
 	 */
 	spin_lock_irq(&port->lock);
-	buf = s->tx_dma_addr + (xmit->tail & (UART_XMIT_SIZE - 1));
+	head = xmit->head;
+	tail = xmit->tail;
+	buf = s->tx_dma_addr + (tail & (UART_XMIT_SIZE - 1));
 	s->tx_dma_len = min_t(unsigned int,
-		CIRC_CNT(xmit->head, xmit->tail, UART_XMIT_SIZE),
-		CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE));
-	spin_unlock_irq(&port->lock);
+		CIRC_CNT(head, tail, UART_XMIT_SIZE),
+		CIRC_CNT_TO_END(head, tail, UART_XMIT_SIZE));
+	if (!s->tx_dma_len) {
+		/* Transmit buffer has been flushed */
+		spin_unlock_irq(&port->lock);
+		return;
+	}
 
 	desc = dmaengine_prep_slave_single(chan, buf, s->tx_dma_len,
 					   DMA_MEM_TO_DEV,
 					   DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 	if (!desc) {
+		spin_unlock_irq(&port->lock);
 		dev_warn(port->dev, "Failed preparing Tx DMA descriptor\n");
 		goto switch_to_pio;
 	}
@@ -1424,18 +1432,18 @@ static void sci_dma_tx_work_fn(struct work_struct *work)
 	dma_sync_single_for_device(chan->device->dev, buf, s->tx_dma_len,
 				   DMA_TO_DEVICE);
 
-	spin_lock_irq(&port->lock);
 	desc->callback = sci_dma_tx_complete;
 	desc->callback_param = s;
-	spin_unlock_irq(&port->lock);
 	s->cookie_tx = dmaengine_submit(desc);
 	if (dma_submit_error(s->cookie_tx)) {
+		spin_unlock_irq(&port->lock);
 		dev_warn(port->dev, "Failed submitting Tx DMA descriptor\n");
 		goto switch_to_pio;
 	}
 
+	spin_unlock_irq(&port->lock);
 	dev_dbg(port->dev, "%s: %p: %d...%d, cookie %d\n",
-		__func__, xmit->buf, xmit->tail, xmit->head, s->cookie_tx);
+		__func__, xmit->buf, tail, head, s->cookie_tx);
 
 	dma_async_issue_pending(chan);
 	return;