From: dillon min <redacted>

To avoid potential deadlock in spin_lock usage, change to use
spin_lock_irqsave(), spin_unlock_irqrestore() in process(thread_fn) context.
spin_lock(), spin_unlock() under handler context.

remove unused local_irq_save/restore call.

Signed-off-by: dillon min <redacted>
---
Was verified on stm32f469-disco board. need more test on stm32mp platform.

 drivers/tty/serial/stm32-usart.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index b3675cf25a69..c4c859b34367 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c

@@ -214,7 +214,7 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
 	struct tty_port *tport = &port->state->port;
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
-	unsigned long c;
+	unsigned long c, flags;
 	u32 sr;
 	char flag;
 

@@ -276,9 +276,17 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
 		uart_insert_char(port, sr, USART_SR_ORE, c, flag);
 	}
 
-	spin_unlock(&port->lock);
+	if (threaded)
+		spin_unlock_irqrestore(&port->lock, flags);
+	else
+		spin_unlock(&port->lock);