After TX dma completes the code will queue another DMA transfer. If
serial8250_tx_dma() fails then there is no plan B to continue the
transfer manually.
This patch enables the TX-fifo empty event so it can be tried again via
DMA or use the manual fallback in case it fails.

Cc: Heikki Krogerus <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
---
 drivers/tty/serial/8250/8250_dma.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dma.c 
b/drivers/tty/serial/8250/8250_dma.c
index 148ffe4..f9ef69f 100644
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -36,8 +36,15 @@ static void __dma_tx_complete(void *param)
        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(&p->port);
 
-       if (!uart_circ_empty(xmit) && !uart_tx_stopped(&p->port))
-               serial8250_tx_dma(p);
+       if (!uart_circ_empty(xmit) && !uart_tx_stopped(&p->port)) {
+               int ret;
+
+               ret = serial8250_tx_dma(p);
+               if (ret && !(p->ier & UART_IER_THRI)) {
+                       p->ier |= UART_IER_THRI;
+                       serial_port_out(&p->port, UART_IER, p->ier);
+               }
+       }
 
        spin_unlock_irqrestore(&p->port.lock, flags);
 }
-- 
2.0.1

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