serial: stm32: fix flow control transfer in DMA mode

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@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20220104182445.4195-4-valentin.caron@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 52755a5..788e002 100644 (file)
--- 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) {