linux-kernel - Re: [PATCH v4 4/4] serial: 8250_dw: fix PSLVERR on RX

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Message-ID: <57d75d55-81e3-445f-a705-e8c116281515@kernel.org>
Date: Fri, 25 Apr 2025 08:41:14 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Yunhui Cui <cuiyunhui@...edance.com>, arnd@...db.de,
 andriy.shevchenko@...ux.intel.com, benjamin.larsson@...exis.eu,
 gregkh@...uxfoundation.org, heikki.krogerus@...ux.intel.com,
 ilpo.jarvinen@...ux.intel.com, 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: Re: [PATCH v4 4/4] serial: 8250_dw: fix PSLVERR on RX_TIMEOUT

On 25. 04. 25, 8:24, Yunhui Cui wrote:
> 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@...edance.com>
> ---
>   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;

No more unsigned char, please. Use u8.

> @@ -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);

s/1/UART_FCR_ENABLE_FIFO/

> +			}
> +
>   			(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);
>   	}
>   


-- 
js
suse labs