[PATCH 20/20] serial: stm32: fix rx interrupt handling in startup

[Bich HEMON]

From: Bich Hemon <bich.hemon at st.com>

When stm32 dma is used, Data register has to be read in order
to clear the RXNE interrupt in case we received data before
usart probe.

Signed-off-by: Bich Hemon <bich.hemon at st.com>
---
 drivers/tty/serial/stm32-usart.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 06a92c8..b1f3aab 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -568,9 +568,18 @@ static int stm32_startup(struct uart_port *port)
 	struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
 	struct stm32_usart_config *cfg = &stm32_port->info->cfg;
 	const char *name = to_platform_device(port->dev)->name;
-	u32 val;
+	u32 val, sr, dr;
 	int ret;
 
+	sr = readl_relaxed(port->membase + ofs->isr);
+
+	if ((sr & USART_SR_RXNE) && (stm32_port->rx_ch))
+		ret = readl_relaxed_poll_timeout_atomic(port->membase +
+							ofs->rdr,
+							dr,
+							!(sr & USART_SR_RXNE),
+							10, 100000);
+
 	ret = request_threaded_irq(port->irq, stm32_interrupt,
 				   stm32_threaded_interrupt,
 				   IRQF_NO_SUSPEND, name, port);
-- 
1.9.1