[PATCH v4 4/4] serial: 8250_dw: fix PSLVERR on RX_TIMEOUT

[Yunhui Cui]

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@xxxxxxxxxxxxx>
---
 drivers/tty/serial/8250/8250_dw.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 07f9be074b4b..1e364280a108 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -273,6 +273,7 @@ static int dw8250_handle_irq(struct uart_port *p)
 	unsigned int quirks = d->pdata->quirks;
 	unsigned int status;
 	unsigned long flags;
+	unsigned char old_fcr;
 
 	/*
 	 * There are ways to get Designware-based UARTs into a state where
@@ -288,9 +289,19 @@ 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) {
+				old_fcr = serial_in(up, UART_FCR);
+				serial_out(up, UART_FCR, old_fcr & ~1);
+			}
+
 			(void) p->serial_in(p, UART_RX);
 
+			if (up->fcr & UART_FCR_ENABLE_FIFO)
+				serial_out(up, UART_FCR, old_fcr);
+		}
+
 		uart_port_unlock_irqrestore(p, flags);
 	}
 
-- 
2.39.2