[PATCH v5 4/4] serial: 8250_dw: fix PSLVERR on RX_TIMEOUT

Yunhui Cui
2025-05-06T11:23:48Z

In the case of RX_TIMEOUT, to avoid PSLVERR, disable the FIFO
before reading UART_RX when UART_LSR_DR is not set.

Fixes: 424d79183af0 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt")
Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
---
drivers/tty/serial/8250/8250_dw.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index f41c4a9ed58b..ffa8cb10b39c 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -288,9 +288,17 @@ static int dw8250_handle_irq(struct uart_port *p)
uart_port_lock_irqsave(p, &flags);
status = serial_lsr_in(up);

- if (!(status & (UART_LSR_DR | UART_LSR_BI)))
+ if (!(status & (UART_LSR_DR | UART_LSR_BI))) {
+ /* To avoid PSLVERR, disable the FIFO first. */
+ if (up->fcr & UART_FCR_ENABLE_FIFO)
+ serial_out(up, UART_FCR, 0);
+
(void) p->serial_in(p, UART_RX);

+ if (up->fcr & UART_FCR_ENABLE_FIFO)
+ serial_out(up, UART_FCR, up->fcr);
+ }
+
uart_port_unlock_irqrestore(p, flags);
}

--
2.39.2