serial: stm32: Return IRQ_NONE in the ISR if no handling happend

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@vger.kernel.org
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/5f92603d0dfd8a5b8014b2b10a902d91e0bb881f.1713344161.git.u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 58d169e5c1db03b910686ac2a229116644f0d6e9..d60cbac691944e131d73d297505d32f04c1cce97 100644 (file)
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -861,6 +861,7 @@ 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);
 
@@ -869,11 +870,14 @@ 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 */
@@ -882,6 +886,7 @@ 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;
        }
 
        /*
@@ -896,6 +901,7 @@ 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;
                }
        }
 
@@ -903,6 +909,7 @@ 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 */
@@ -912,9 +919,10 @@ 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)