Re: [PATCH v7 4/4] serial: 8250_dw: fix PSLVERR on RX_TIMEOUT

Greg KH
2025-06-06T10:41:12Z

On Wed, May 28, 2025 at 02:26:09PM +0800, Yunhui Cui 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@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 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);
> }
>
> --
> 2.39.5
>
>

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him
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