Re: [PATCH v9 2/4] serial: 8250_dw: fix PSLVERR on RX_TIMEOUT

[yunhui cui]

Hi John,


On Tue, Jun 10, 2025 at 5:22 PM Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  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);
>         }
>
> --
> 2.39.5
>

Any comments on this patch?

Thanks,
Yunhui