@@ -553,19 +553,22 @@ static void atmel_stop_tx(struct uart_port *port)
{
struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
bool is_pdc = atmel_use_pdc_tx(port);
+ bool is_dma = is_pdc || atmel_use_dma_tx(port);
if (is_pdc) {
/* disable PDC transmit */
atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
}
- /*
- * Disable the transmitter.
- * This is mandatory when DMA is used, otherwise the DMA buffer
- * is fully transmitted.
- */
- atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);
- atmel_port->tx_stopped = true;
+ if (is_dma) {
+ /*
+ * Disable the transmitter.
+ * This is mandatory when DMA is used, otherwise the DMA buffer
+ * is fully transmitted.
+ */
+ atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);
+ atmel_port->tx_stopped = true;
+ }
/* Disable interrupts */
atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
@@ -601,9 +604,11 @@ static void atmel_start_tx(struct uart_port *port)
/* Enable interrupts */
atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);
- /* re-enable the transmitter */
- atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
- atmel_port->tx_stopped = false;
+ if (is_dma) {
+ /* re-enable the transmitter */
+ atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
+ atmel_port->tx_stopped = false;
+ }
}
/*
Writing ATMEL_US_TXDIS to ATMEL_US_CR makes the transmitter NOT to send the just queued character. This means when the character is last and uart calls ops->stop_tx(), the character is not sent at all. The usart datasheet is not much specific on this, it just says the transmitter is stopped. But apparently, the character is dropped. So we should stop the transmitter only for DMA and PDC transfers to not send any more characters. For PIO, this is unexpected and deviates from other drivers. In particular, the below referenced commit broke TX as it added a call to ->stop_tx() after the very last character written to the transmitter. So fix this by limiting the write of ATMEL_US_TXDIS to DMA transfers only. Even there, I don't know if it is correctly implemented. Are all the queued characters sent once ->start_tx() is called? Anyone tested flow control -- be it hard (RTSCTS) or the soft (XOFF/XON) one? Fixes: 2d141e683e9a ("tty: serial: use uart_port_tx() helper") Cc: Richard Genoud <richard.genoud@gmail.com> Cc: Nicolas Ferre <nicolas.ferre@microchip.com> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com> Cc: Claudiu Beznea <claudiu.beznea@microchip.com> Cc: linux-arm-kernel@lists.infradead.org Reported-by: Michael Walle <michael@walle.cc> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org> --- drivers/tty/serial/atmel_serial.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-)