[PATCH 3/4] serial: stm32: fix flow control transfer in DMA mode

[Valentin Caron]

If flow control is enabled, framework will call stop_tx to
pause transfer and then call start_tx to resume transfer.

Clear USART_CR3_DMAT bit in stop_tx ops to pause DMA transfer.

Signed-off-by: Erwan Le Ray <erwan.leray at foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron at foss.st.com>
---
 drivers/tty/serial/stm32-usart.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 52755a576bc2..788e002688f2 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -707,8 +707,11 @@ static void stm32_usart_stop_tx(struct uart_port *port)
 {
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	struct serial_rs485 *rs485conf = &port->rs485;
+	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
 
 	stm32_usart_tx_interrupt_disable(port);
+	if (stm32_usart_tx_dma_started(stm32_port) && stm32_usart_tx_dma_enabled(stm32_port))
+		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
 
 	if (rs485conf->flags & SER_RS485_ENABLED) {
 		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
-- 
2.17.1