[PATCH 13/13] serial: stm32: add support for "flush_buffer" ops

[Erwan Le Ray]

Add the support for "flush_buffer" ops in order to flush any write buffers,
reset any DMA state and stop any ongoing DMA transfers when the
port->state->xmit circular buffer is cleared.

Signed-off-by: Erwan Le Ray <erwan.le...@foss.st.com>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 114408f3892a..92836068e5ec 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -597,6 +597,19 @@ static void stm32_usart_start_tx(struct uart_port *port)
        stm32_usart_transmit_chars(port);
 }
 
+/* Flush the transmit buffer. */
+static void stm32_usart_flush_buffer(struct uart_port *port)
+{
+       struct stm32_port *stm32_port = to_stm32_port(port);
+       struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+
+       if (stm32_port->tx_ch) {
+               dmaengine_terminate_async(stm32_port->tx_ch);
+               stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
+               stm32_port->tx_dma_busy = false;
+       }
+}
+
 /* Throttle the remote when input buffer is about to overflow. */
 static void stm32_usart_throttle(struct uart_port *port)
 {
@@ -992,6 +1005,7 @@ static const struct uart_ops stm32_uart_ops = {
        .break_ctl      = stm32_usart_break_ctl,
        .startup        = stm32_usart_startup,
        .shutdown       = stm32_usart_shutdown,
+       .flush_buffer   = stm32_usart_flush_buffer,
        .set_termios    = stm32_usart_set_termios,
        .pm             = stm32_usart_pm,
        .type           = stm32_usart_type,
-- 
2.17.1