[PATCH 1/2] serial: stm32: Return IRQ_NONE in the ISR if no handling happend

[Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>]

If there is a stuck irq that the handler doesn't address, returning
IRQ_HANDLED unconditionally makes it impossible for the irq core to
detect the problem and disable the irq. So only return IRQ_HANDLED if
an event was handled.

A stuck irq is still problematic, but with this change at least it only
makes the UART nonfunctional instead of occupying the (usually only) CPU
by 100% and so stall the whole machine.

Fixes: 48a6092fb41f ("serial: stm32-usart: Add STM32 USART Driver")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
---
 drivers/tty/serial/stm32-usart.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 8c66abcfe6ca..2bea1d7c9858 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -849,6 +849,7 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
 	u32 sr;
 	unsigned int size;
+	irqreturn_t ret = IRQ_NONE;
 
 	sr = readl_relaxed(port->membase + ofs->isr);
 
@@ -857,11 +858,14 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 	    (sr & USART_SR_TC)) {
 		stm32_usart_tc_interrupt_disable(port);
 		stm32_usart_rs485_rts_disable(port);
+		ret = IRQ_HANDLED;
 	}
 
-	if ((sr & USART_SR_RTOF) && ofs->icr != UNDEF_REG)
+	if ((sr & USART_SR_RTOF) && ofs->icr != UNDEF_REG) {
 		writel_relaxed(USART_ICR_RTOCF,
 			       port->membase + ofs->icr);
+		ret = IRQ_HANDLED;
+	}
 
 	if ((sr & USART_SR_WUF) && ofs->icr != UNDEF_REG) {
 		/* Clear wake up flag and disable wake up interrupt */
@@ -870,6 +874,7 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_WUFIE);
 		if (irqd_is_wakeup_set(irq_get_irq_data(port->irq)))
 			pm_wakeup_event(tport->tty->dev, 0);
+		ret = IRQ_HANDLED;
 	}
 
 	/*
@@ -884,6 +889,7 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 			uart_unlock_and_check_sysrq(port);
 			if (size)
 				tty_flip_buffer_push(tport);
+			ret = IRQ_HANDLED;
 		}
 	}
 
@@ -891,6 +897,7 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 		uart_port_lock(port);
 		stm32_usart_transmit_chars(port);
 		uart_port_unlock(port);
+		ret = IRQ_HANDLED;
 	}
 
 	/* Receiver timeout irq for DMA RX */
@@ -900,9 +907,10 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 		uart_unlock_and_check_sysrq(port);
 		if (size)
 			tty_flip_buffer_push(tport);
+		ret = IRQ_HANDLED;
 	}
 
-	return IRQ_HANDLED;
+	return ret;
 }
 
 static void stm32_usart_set_mctrl(struct uart_port *port, unsigned int mctrl)
-- 
2.43.0