[PATCH v4 02/13] serial: 8250: use THRE & __stop_tx also with DMA

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

8250 DMA tx complete path lacks calls to normal 8250 stop handling. It
does not use THRE to detect true completion of the tx and also doesn't
call __stop_tx. This leads to problems with em485 that needs to handle
RTS timing.

Instead of handling tx stop internally within 8250 dma code, enable
THRE when tx'able data runs out and tweak serial8250_handle_irq to call
only __stop_tx when uart is using DMA.

It also seems bit early to call serial8250_rpm_put_tx from there while
tx is still underway(?).

Tested-by: Vicente Bergas <vicencb@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 drivers/tty/serial/8250/8250_dma.c  | 3 +--
 drivers/tty/serial/8250/8250_port.c | 9 ++++++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 890fa7ddaa7f..e1625a73ce57 100644
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -34,7 +34,7 @@ static void __dma_tx_complete(void *param)
 		uart_write_wakeup(&p->port);
 
 	ret = serial8250_tx_dma(p);
-	if (ret)
+	if (ret || !dma->tx_running)
 		serial8250_set_THRI(p);
 
 	spin_unlock_irqrestore(&p->port.lock, flags);
@@ -71,7 +71,6 @@ int serial8250_tx_dma(struct uart_8250_port *p)
 
 	if (uart_tx_stopped(&p->port) || uart_circ_empty(xmit)) {
 		/* We have been called from __dma_tx_complete() */
-		serial8250_rpm_put_tx(p);
 		return 0;
 	}
 
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index d30a6c1c4c20..40b62126c1ca 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1950,9 +1950,12 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
 			status = serial8250_rx_chars(up, status);
 	}
 	serial8250_modem_status(up);
-	if ((!up->dma || up->dma->tx_err) && (status & UART_LSR_THRE) &&
-		(up->ier & UART_IER_THRI))
-		serial8250_tx_chars(up);
+	if ((status & UART_LSR_THRE) && (up->ier & UART_IER_THRI)) {
+		if (!up->dma || up->dma->tx_err)
+			serial8250_tx_chars(up);
+		else
+			__stop_tx(up);
+	}
 
 	uart_unlock_and_check_sysrq_irqrestore(port, flags);
 
-- 
2.30.2