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

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Message-ID: <9d4e7002-48fe-4fa0-8e23-7c2160419910@kernel.org>
Date: Fri, 25 Apr 2025 08:43:22 +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, 8:41, 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?

>> +                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