1 files changed, 33 insertions, 4 deletions

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index cfdda35499e6..7fd192e1e15d 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -577,9 +577,12 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 	 * rx errors in dma mode has to be handled ASAP to avoid overrun as the DMA request
 	 * line has been masked by HW and rx data are stacking in FIFO.
 	 */
-	if (((sr & USART_SR_RXNE) && !stm32_usart_rx_dma_enabled(port)) ||
-	    ((sr & USART_SR_ERR_MASK) && stm32_usart_rx_dma_enabled(port)))
-		stm32_usart_receive_chars(port, false);
+	if (!stm32_port->throttled) {
+		if (((sr & USART_SR_RXNE) && !stm32_usart_rx_dma_enabled(port)) ||
+		    ((sr & USART_SR_ERR_MASK) && stm32_usart_rx_dma_enabled(port))) {
+			stm32_usart_receive_chars(port, false);
+		}
+	}
 
 	if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) {
 		spin_lock(&port->lock);
@@ -596,9 +599,11 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
 {
 	struct uart_port *port = ptr;
+	struct stm32_port *stm32_port = to_stm32_port(port);
 
 	/* Receiver timeout irq for DMA RX */
-	stm32_usart_receive_chars(port, false);
+	if (!stm32_port->throttled)
+		stm32_usart_receive_chars(port, false);
 
 	return IRQ_HANDLED;
 }
@@ -711,10 +716,19 @@ static void stm32_usart_throttle(struct uart_port *port)
 	unsigned long flags;
 
 	spin_lock_irqsave(&port->lock, flags);
+
+	/*
+	 * Disable DMA request line if enabled, so the RX data gets queued into the FIFO.
+	 * Hardware flow control is triggered when RX FIFO is full.
+	 */
+	if (stm32_usart_rx_dma_enabled(port))
+		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAR);
+
 	stm32_usart_clr_bits(port, ofs->cr1, stm32_port->cr1_irq);
 	if (stm32_port->cr3_irq)
 		stm32_usart_clr_bits(port, ofs->cr3, stm32_port->cr3_irq);
 
+	stm32_port->throttled = true;
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
@@ -730,6 +744,14 @@ static void stm32_usart_unthrottle(struct uart_port *port)
 	if (stm32_port->cr3_irq)
 		stm32_usart_set_bits(port, ofs->cr3, stm32_port->cr3_irq);
 
+	/*
+	 * Switch back to DMA mode (re-enable DMA request line).
+	 * Hardware flow control is stopped when FIFO is not full any more.
+	 */
+	if (stm32_port->rx_ch)
+		stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAR);
+
+	stm32_port->throttled = false;
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
@@ -775,6 +797,13 @@ static int stm32_usart_startup(struct uart_port *port)
 	if (ofs->rqr != UNDEF_REG)
 		writel_relaxed(USART_RQR_RXFRQ, port->membase + ofs->rqr);
 
+	/*
+	 * DMA request line not re-enabled at resume when port is throttled.
+	 * It will be re-enabled by unthrottle ops.
+	 */
+	if (!stm32_port->throttled)
+		stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAR);
+
 	/* RX enabling */
 	val = stm32_port->cr1_irq | USART_CR1_RE | BIT(cfg->uart_enable_bit);
 	stm32_usart_set_bits(port, ofs->cr1, val);