serial: 8250: use THRE & __stop_tx also with DMA

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>
Link: https://lore.kernel.org/r/20220425143410.12703-3-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 1bdc8d6432fef9e841b57886e794a6b7a506ee93..7133fceed35e35100398f0994038c36cf4ce4e30 100644 (file)
--- 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);
@@ -80,7 +80,6 @@ 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 5bba852d30f79579a277a9b3b276ab7fdfb78248..40d4895fd208fddae717ca60faf40461baa8ee2d 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1948,9 +1948,12 @@ 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);