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

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Message-ID: <CAEEQ3w=MOSU2mNo8qq8qz9KE9M0Zb55xeS9aw1263osXtP+8SA@mail.gmail.com>
Date: Sun, 27 Apr 2025 19:17:53 +0800
From: yunhui cui <cuiyunhui@...edance.com>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: 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: [External] Re: [PATCH v4 4/4] serial: 8250_dw: fix PSLVERR on RX_TIMEOUT

Hi js,


On Fri, Apr 25, 2025 at 2:43 PM Jiri Slaby <jirislaby@...nel.org> wrote:
>
> On 25. 04. 25, 8:41, Jiri Slaby wrote:
> > 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);
>
> Wait, read(FCR) actually means read(IIR). FCR is write only. Or is DW
> special in this?

Indeed, the valid bits of the FCR are write-only. It seems that here
we can only do serial_out(up, UART_FCR, up->fcr); What do you think?

>
> >> +                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
>

Thanks,
Yunhui