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@bytedance.com Cc: stable@vger.kernel.org --- 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 1902f29444a1c..082b7fcf251db 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -297,9 +297,17 @@ 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); }