serial: imx: Fix x_char handling and tx flow control

The serial core expects the UART driver to transmit x_char
(START/STOP chars) even if tx is stopped and before data already
in the tx ring buffer if possible. Also, sending x_char must
not cause additional data in the tx ring buffer to transmit
if tx is stopped.

Cause x_char to be transmitted before any other data is sent.
Auto-stop tx if the tx ring buffer is empty or tx should be stopped.
Only perform one write wakeup if tx ring buffer space is below
threshold.

x_char handling in DMA mode is still broken; add FIXME.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 044e86d528aef9bfa5c705d40f1997e5fc9e92e3..c86f1538bfddd90e730bcd95a0efa9789d4968db 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -464,9 +464,19 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
 {
        struct circ_buf *xmit = &sport->port.state->xmit;
 
+       if (sport->port.x_char) {
+               /* Send next char */
+               writel(sport->port.x_char, sport->port.membase + URTX0);
+               return;
+       }
+
+       if (uart_circ_empty(xmit) || uart_tx_stopped(&sport->port)) {
+               imx_stop_tx(&sport->port);
+               return;
+       }
+
        while (!uart_circ_empty(xmit) &&
-                       !(readl(sport->port.membase + uts_reg(sport))
-                               & UTS_TXFULL)) {
+              !(readl(sport->port.membase + uts_reg(sport)) & UTS_TXFULL)) {
                /* send xmit->buf[xmit->tail]
                 * out the port here */
                writel(xmit->buf[xmit->tail], sport->port.membase + URTX0);
@@ -567,9 +577,6 @@ static void imx_start_tx(struct uart_port *port)
        struct imx_port *sport = (struct imx_port *)port;
        unsigned long temp;
 
-       if (uart_circ_empty(&port->state->xmit))
-               return;
-
        if (USE_IRDA(sport)) {
                /* half duplex in IrDA mode; have to disable receive mode */
                temp = readl(sport->port.membase + UCR4);
@@ -604,7 +611,10 @@ static void imx_start_tx(struct uart_port *port)
        }
 
        if (sport->dma_is_enabled) {
-               imx_dma_tx(sport);
+               /* FIXME: port->x_char must be transmitted if != 0 */
+               if (!uart_circ_empty(&port->state->xmit) &&
+                   !uart_tx_stopped(port))
+                       imx_dma_tx(sport);
                return;
        }
 
@@ -632,27 +642,10 @@ static irqreturn_t imx_rtsint(int irq, void *dev_id)
 static irqreturn_t imx_txint(int irq, void *dev_id)
 {
        struct imx_port *sport = dev_id;
-       struct circ_buf *xmit = &sport->port.state->xmit;
        unsigned long flags;
 
        spin_lock_irqsave(&sport->port.lock, flags);
-       if (sport->port.x_char) {
-               /* Send next char */
-               writel(sport->port.x_char, sport->port.membase + URTX0);
-               goto out;
-       }
-
-       if (uart_circ_empty(xmit) || uart_tx_stopped(&sport->port)) {
-               imx_stop_tx(&sport->port);
-               goto out;
-       }
-
        imx_transmit_buffer(sport);
-
-       if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
-               uart_write_wakeup(&sport->port);
-
-out:
        spin_unlock_irqrestore(&sport->port.lock, flags);
        return IRQ_HANDLED;
 }