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serial: imx: Fix x_char handling and tx flow control

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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>
This commit is contained in:
Peter Hurley 2014-09-02 17:39:12 -04:00 committed by Greg Kroah-Hartman
parent 99abf3b924
commit 5e42e9a30c
1 changed files with 16 additions and 23 deletions
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39
drivers/tty/serial/imx.c
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@ -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;
}