linux-kernel - [PATCH v6 4/4] serial: 8250_dw: fix PSLVERR on RX

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Message-Id: <20250513024212.74658-4-cuiyunhui@bytedance.com>
Date: Tue, 13 May 2025 10:42:12 +0800
From: Yunhui Cui <cuiyunhui@...edance.com>
To: arnd@...db.de,
	andriy.shevchenko@...ux.intel.com,
	benjamin.larsson@...exis.eu,
	cuiyunhui@...edance.com,
	gregkh@...uxfoundation.org,
	heikki.krogerus@...ux.intel.com,
	ilpo.jarvinen@...ux.intel.com,
	jirislaby@...nel.org,
	jkeeping@...usicbrands.com,
	john.ogness@...utronix.de,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	markus.mayer@...aro.org,
	matt.porter@...aro.org,
	namcao@...utronix.de,
	paulmck@...nel.org,
	pmladek@...e.com,
	schnelle@...ux.ibm.com,
	sunilvl@...tanamicro.com,
	tim.kryger@...aro.org
Subject: [PATCH v6 4/4] serial: 8250_dw: fix PSLVERR on RX_TIMEOUT

The DW UART may trigger the RX_TIMEOUT interrupt without data
present and remain stuck in this state indefinitely. The
dw8250_handle_irq() function detects this condition by checking
if the UART_LSR_DR bit is not set when RX_TIMEOUT occurs. When
detected, it performs a "dummy read" to recover the DW UART from
this state.

When the PSLVERR_RESP_EN parameter is set to 1, reading the UART_RX
while the FIFO is enabled and UART_LSR_DR is not set will generate a
PSLVERR error, which may lead to a system panic. There are two methods
to prevent PSLVERR: one is to check if UART_LSR_DR is set before reading
UART_RX when the FIFO is enabled, and the other is to read UART_RX when
the FIFO is disabled.

Given these two scenarios, the FIFO must be disabled before the
"dummy read" operation and re-enabled afterward to maintain normal
UART functionality.

Fixes: 424d79183af0 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt")
Signed-off-by: Yunhui Cui <cuiyunhui@...edance.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 8b0018fadccea..686f9117a3339 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -301,9 +301,17 @@ 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);
+
 			serial_port_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