linux-kernel - Re: [PATCH] tty/serial: atmel: fix RS485 half duplex with DMA

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Message-ID: <575E822F.7050501@atmel.com>
Date:	Mon, 13 Jun 2016 11:51:43 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-serial@...r.kernel.org>
CC:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty/serial: atmel: fix RS485 half duplex with DMA

Le 02/06/2016 12:41, Nicolas Ferre a écrit :
> Le 28/05/2016 00:54, Alexandre Belloni a écrit :
>> When using DMA, half duplex doesn't work properly because rx is not stopped
>> before starting tx. Ensure we call atmel_stop_rx() in the DMA case.
>>
>> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> 
> Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>
> 
> We can also add:
> Cc: <stable@...r.kernel.org> # v4.3+
> 
> 
> Thanks Alexandre!

Greg,

It's not a regression but a good fix for this rs485 mode. So I suspect
it can still be queued for 4.7-rc... (aka: gentle ping).

Bye,

>> ---
>>  drivers/tty/serial/atmel_serial.c | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> index 954941dd8124..f9c798cba83f 100644
>> --- a/drivers/tty/serial/atmel_serial.c
>> +++ b/drivers/tty/serial/atmel_serial.c
>> @@ -482,19 +482,21 @@ static void atmel_start_tx(struct uart_port *port)
>>  {
>>  	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
>>  
>> -	if (atmel_use_pdc_tx(port)) {
>> -		if (atmel_uart_readl(port, ATMEL_PDC_PTSR) & ATMEL_PDC_TXTEN)
>> -			/* The transmitter is already running.  Yes, we
>> -			   really need this.*/
>> -			return;
>> +	if (atmel_use_pdc_tx(port) && (atmel_uart_readl(port, ATMEL_PDC_PTSR)
>> +				       & ATMEL_PDC_TXTEN))
>> +		/* The transmitter is already running.  Yes, we
>> +		   really need this.*/
>> +		return;
>>  
>> +	if (atmel_use_pdc_tx(port) || atmel_use_dma_tx(port))
>>  		if ((port->rs485.flags & SER_RS485_ENABLED) &&
>>  		    !(port->rs485.flags & SER_RS485_RX_DURING_TX))
>>  			atmel_stop_rx(port);
>>  
>> +	if (atmel_use_pdc_tx(port))
>>  		/* re-enable PDC transmit */
>>  		atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTEN);
>> -	}
>> +
>>  	/* Enable interrupts */
>>  	atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);
>>  }
>>
> 
> 


-- 
Nicolas Ferre