[PATCH 4/6] Serial: AT91: Enable tx dma

@@ -590,6 +590,39 @@ static void atmel_tx_chars(struct uart_port *port)
 		UART_PUT_IER(port, atmel_port->tx_done_mask);
 }
 
+static void atmel_dma_tx_complete(void *arg)
+{
+	struct atmel_uart_port *atmel_port = arg;
+	struct uart_port *port = &atmel_port->uart;
+	struct circ_buf *xmit = &port->state->xmit;
+	struct dma_chan *chan = atmel_port->chan_tx;
+	unsigned long flags;
+
+	spin_lock_irqsave(&port->lock, flags);
+
+	if (chan)
+		dmaengine_terminate_all(chan);
+	xmit->tail += sg_dma_len(&atmel_port->sg_tx);
+	xmit->tail &= UART_XMIT_SIZE - 1;
+
+	port->icount.tx += sg_dma_len(&atmel_port->sg_tx);
+
+	spin_lock_irq(&atmel_port->lock_tx);
+	async_tx_ack(atmel_port->desc_tx);
+	atmel_port->cookie_tx = -EINVAL;
+	atmel_port->desc_tx = NULL;
+	spin_unlock_irq(&atmel_port->lock_tx);
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(port);
+
+	/* Do we really need this? */
+	if (!uart_circ_empty(xmit))
+		tasklet_schedule(&atmel_port->tasklet);
+
+	spin_unlock_irqrestore(&port->lock, flags);
+}
+
 static void atmel_tx_dma_release(struct atmel_uart_port *atmel_port)
 {
 	struct dma_chan *chan = atmel_port->chan_tx;

@@ -602,6 +635,70 @@ static void atmel_tx_dma_release(struct atmel_uart_port *atmel_port)
 	}
 }
 
+/*
+ * Called from tasklet with TXRDY interrupt is disabled.
+ */
+static void atmel_tx_dma(struct uart_port *port)
+{
+	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
+	struct circ_buf *xmit = &port->state->xmit;
+	struct dma_chan *chan = atmel_port->chan_tx;
+	struct dma_async_tx_descriptor *desc;
+	struct scatterlist *sg = &atmel_port->sg_tx;
+
+	/* Make sure we have an idle channel */
+	if (atmel_port->desc_tx != NULL)
+		return;
+
+	if (!uart_circ_empty(xmit) && !uart_tx_stopped(port)) {
+		/*
+		 * DMA is idle now.
+		 * Port xmit buffer is already mapped,
+		 * and it is one page... Just adjust
+		 * offsets and lengths. Since it is a circular buffer,
+		 * we have to transmit till the end, and then the rest.
+		 * Take the port lock to get a
+		 * consistent xmit buffer state.
+		 */
+		sg->offset = xmit->tail & (UART_XMIT_SIZE - 1);
+		sg_dma_address(sg) = (sg_dma_address(sg) &
+					~(UART_XMIT_SIZE - 1))
+					+ sg->offset;
+		sg_dma_len(sg) = CIRC_CNT_TO_END(xmit->head,
+						xmit->tail,
+						UART_XMIT_SIZE);
+		BUG_ON(!sg_dma_len(sg));
+
+		desc = dmaengine_prep_slave_sg(chan,
+						sg,
+						atmel_port->sg_len_tx,
+						DMA_MEM_TO_DEV,
+						DMA_PREP_INTERRUPT |
+						DMA_CTRL_ACK);
+		if (!desc) {
+			dev_err(port->dev, "Failed to send via dma!\n");
+			return;
+		}
+
+		dma_sync_sg_for_device(port->dev, sg, 1, DMA_MEM_TO_DEV);
+
+		atmel_port->desc_tx = desc;
+		desc->callback = atmel_dma_tx_complete;
+		desc->callback_param = atmel_port;
+		atmel_port->cookie_tx = dmaengine_submit(desc);
+
+		dma_async_issue_pending(chan);
+	} else {
+		if (atmel_port->rs485.flags & SER_RS485_ENABLED) {
+			/* DMA done, stop TX, start RX for RS485 */
+			atmel_start_rx(port);
+		}
+	}
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(port);
+}
+
 static bool filter(struct dma_chan *chan, void *slave)
 {
 	struct	at_dma_slave		*sl = slave;

@@ -991,6 +1088,8 @@ static void atmel_tasklet_func(unsigned long data)
 
 	if (atmel_use_pdc_tx(port))
 		atmel_tx_pdc(port);
+	else if (atmel_use_dma_tx(port))
+		atmel_tx_dma(port);
 	else
 		atmel_tx_chars(port);