serial: imx: Support sw flow control in DMA mode

This patch adds Software flow control support in DMA mode.

Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 28 insertions, 2 deletions

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 5a7da019f01a..72b800b296b1 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -464,9 +464,11 @@ static void imx_enable_ms(struct uart_port *port)
         mod_timer(&sport->timer, jiffies);
 }
 
+static void imx_dma_tx(struct imx_port *sport);
 static inline void imx_transmit_buffer(struct imx_port *sport)
 {
         struct circ_buf *xmit = &sport->port.state->xmit;
+        unsigned long temp;
 
         if (sport->port.x_char) {
                 /* Send next char */
@@ -481,6 +483,22 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
                 return;
         }
 
+        if (sport->dma_is_enabled) {
+                /*
+                 * We've just sent a X-char Ensure the TX DMA is enabled
+                 * and the TX IRQ is disabled.
+                 **/
+                temp = readl(sport->port.membase + UCR1);
+                temp &= ~UCR1_TXMPTYEN;
+                if (sport->dma_is_txing) {
+                        temp |= UCR1_TDMAEN;
+                        writel(temp, sport->port.membase + UCR1);
+                } else {
+                        writel(temp, sport->port.membase + UCR1);
+                        imx_dma_tx(sport);
+                }
+        }
+
         while (!uart_circ_empty(xmit) &&
                !(readl(sport->port.membase + uts_reg(sport)) & UTS_TXFULL)) {
                 /* send xmit->buf[xmit->tail]
@@ -497,7 +515,6 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
                 imx_stop_tx(&sport->port);
 }
 
-static void imx_dma_tx(struct imx_port *sport);
 static void dma_tx_callback(void *data)
 {
         struct imx_port *sport = data;
@@ -630,7 +647,16 @@ static void imx_start_tx(struct uart_port *port)
         }
 
         if (sport->dma_is_enabled) {
-                /* FIXME: port->x_char must be transmitted if != 0 */
+                if (sport->port.x_char) {
+                        /* We have X-char to send, so enable TX IRQ and
+                         * disable TX DMA to let TX interrupt to send X-char */
+                        temp = readl(sport->port.membase + UCR1);
+                        temp &= ~UCR1_TDMAEN;
+                        temp |= UCR1_TXMPTYEN;
+                        writel(temp, sport->port.membase + UCR1);
+                        return;
+                }
+
                 if (!uart_circ_empty(&port->state->xmit) &&
                     !uart_tx_stopped(port))
                         imx_dma_tx(sport);