serial: stm32: Merge hard IRQ and threaded IRQ handling into single IRQ handler

Requesting an interrupt with IRQF_ONESHOT will run the primary handler
in the hard-IRQ context even in the force-threaded mode. The
force-threaded mode is used by PREEMPT_RT in order to avoid acquiring
sleeping locks (spinlock_t) in hard-IRQ context. This combination
makes it impossible and leads to "sleeping while atomic" warnings.

Use one interrupt handler for both handlers (primary and secondary)
and drop the IRQF_ONESHOT flag which is not needed.

Fixes: e359b44 ("serial: stm32: fix threaded interrupt handling")
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Valentin Caron <valentin.caron@foss.st.com> # V3
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230112180417.25595-1-marex@denx.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Marek Vasut

drivers/tty/serial/stm32-usart.c

@@ -797,23 +797,9 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 		spin_unlock(&port->lock);
 	}
 
-	if (stm32_usart_rx_dma_enabled(port))
-		return IRQ_WAKE_THREAD;
-	else
-		return IRQ_HANDLED;
-}
-
-static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
-{
-	struct uart_port *port = ptr;
-	struct tty_port *tport = &port->state->port;
-	struct stm32_port *stm32_port = to_stm32_port(port);
-	unsigned int size;
-	unsigned long flags;
-
 	/* Receiver timeout irq for DMA RX */
-	if (!stm32_port->throttled) {
-		spin_lock_irqsave(&port->lock, flags);
+	if (stm32_usart_rx_dma_enabled(port) && !stm32_port->throttled) {
+		spin_lock(&port->lock);
 		size = stm32_usart_receive_chars(port, false);
 		uart_unlock_and_check_sysrq_irqrestore(port, flags);
 		if (size)
@@ -1015,10 +1001,8 @@ static int stm32_usart_startup(struct uart_port *port)
 	u32 val;
 	int ret;
 
-	ret = request_threaded_irq(port->irq, stm32_usart_interrupt,
-				   stm32_usart_threaded_interrupt,
-				   IRQF_ONESHOT | IRQF_NO_SUSPEND,
-				   name, port);
+	ret = request_irq(port->irq, stm32_usart_interrupt,
+			  IRQF_NO_SUSPEND, name, port);
 	if (ret)
 		return ret;
 
@@ -1601,13 +1585,6 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
 	struct dma_slave_config config;
 	int ret;
 
-	/*
-	 * Using DMA and threaded handler for the console could lead to
-	 * deadlocks.
-	 */
-	if (uart_console(port))
-		return -ENODEV;
-
 	stm32port->rx_buf = dma_alloc_coherent(dev, RX_BUF_L,
 					       &stm32port->rx_dma_buf,
 					       GFP_KERNEL);