linux-kernel - Re: [PATCH] tty/serial: atmel_serial: BUG: stop DMA from transmitting in stop

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Date:   Mon, 2 Jan 2017 15:16:46 +0100
From:   Richard Genoud <richard.genoud@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Nicolas Ferre <nicolas.ferre@...el.com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "beware, this won't apply before 4.3" <stable@...r.kernel.org>
Subject: Re: [PATCH] tty/serial: atmel_serial: BUG: stop DMA from transmitting
 in stop_tx

2017-01-02 12:13 GMT+01:00 Nicolas Ferre <nicolas.ferre@...el.com>:
> Le 13/12/2016 à 17:27, Richard Genoud a écrit :
>> If we don't disable the transmitter in atmel_stop_tx, the DMA buffer
>> continues to send data until it is emptied.
>> This cause problems with the flow control (CTS is asserted and data are
>> still sent).
>>
>> So, disabling the transmitter in atmel_stop_tx is a sane thing to do.
>>
>> Tested on at91sam9g35-cm(DMA)
>> Tested for regressions on sama5d2-xplained(Fifo) and at91sam9g20ek(PDC)
>>
>> Cc: <stable@...r.kernel.org> (beware, this won't apply before 4.3)
>> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
>
> Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>
>
>> ---
>>  drivers/tty/serial/atmel_serial.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> NB: this is not for the 4.10 merge window, I'm just sending it now to
>> have some comments if someone is againts it.
>>
>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> index 168b10cad47b..f9d42de5ab2d 100644
>> --- a/drivers/tty/serial/atmel_serial.c
>> +++ b/drivers/tty/serial/atmel_serial.c
>> @@ -481,6 +481,14 @@ static void atmel_stop_tx(struct uart_port *port)
>>               /* disable PDC transmit */
>>               atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
>>       }
>> +
>> +     /*
>> +      * Disable the transmitter.
>> +      * This is mandatory when DMA is used, otherwise the DMA buffer
>> +      * is fully transmitted.
>> +      */
>> +     atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);
>> +
>>       /* Disable interrupts */
>>       atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
>>
>> @@ -513,6 +521,9 @@ static void atmel_start_tx(struct uart_port *port)
>>
>>       /* Enable interrupts */
>>       atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);
>> +
>> +     /* re-enable the transmitter */
>> +     atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
>>  }
>>
>>  /*
>>
>
>
> --
> Nicolas Ferre

Greg, could you also take this patch in your tree ?

Thanks !

Richard.