linux-kernel - Re: [PATCHv2 3/3] tty/serial: at91: fix hardware handshake on SAM9x5 (without GPIOs)

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Date:   Mon, 12 Sep 2016 12:50:38 +0200
From:   Richard Genoud <richard.genoud@...il.com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:     Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Nicolas Ferre <nicolas.ferre@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 3/3] tty/serial: at91: fix hardware handshake on SAM9x5
 (without GPIOs)

2016-09-12 11:53 GMT+02:00 Alexandre Belloni
<alexandre.belloni@...e-electrons.com>:
> On 12/09/2016 at 11:47:33 +0200, Richard Genoud wrote :
>> Commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
>> hardware handshake is enabled") broke the hardware handshake on SAM9x5
>> platforms.
>>
>> On Atmel platforms, the USART can only handle the handware handshake
>> (ATMEL_US_USMODE_HWHS) if FIFOs or PDC are used.
>>
>> Thus, ATMEL_US_USMODE_HWHS mode should only be used in this case.
>>
>> For SAM9x5, there's no FIFOs nor PDC for the USART, so the mode should
>> be ATMEL_US_USMODE_NORMAL and the RTS pin should be controlled by the
>> driver.
>>
>> NB: -stable is not Cced because it doesn't cleanly apply on 4.1+
>>
>> Tested on SAM9G35-CM with and without DMA
>>
>> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
>> Fixes: 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when hardware handshake is enabled")
>> ---
>>  drivers/tty/serial/atmel_serial.c | 18 +++++++++++-------
>>  1 file changed, 11 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> index e9b4fbf88c2d..32154e7231ce 100644
>> --- a/drivers/tty/serial/atmel_serial.c
>> +++ b/drivers/tty/serial/atmel_serial.c
>> @@ -2130,15 +2130,19 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>>       } else if ((termios->c_cflag & CRTSCTS) &&
>>                  !mctrl_gpio_use_rtscts(atmel_port->gpios)) {
>>               /*
>> -              * RS232 with hardware handshake (RTS/CTS)
>> -              * handled by the controller.
>> +              * Automatic hardware handshake (RTS/CTS) only work with
>> +              * FIFOs or PDC.
>> +              * Meaning that on SAM9x5 the controller can't handle
>> +              * the hardware handshake (no FIFOs nor PDC on these platforms).
>>                */
>> -             if (atmel_use_dma_rx(port) && !atmel_use_fifo(port)) {
>> -                     dev_info(port->dev, "not enabling hardware flow control because DMA is used");
>> -                     termios->c_cflag &= ~CRTSCTS;
>> -             } else {
>> +             if (atmel_use_pdc_rx(port) || atmel_use_fifo(port))
>>                       mode |= ATMEL_US_USMODE_HWHS;
>> -             }
>> +             else
>> +                     /*
>> +                      * The hardware handshake won't be handle by the
>> +                      * controller but by the driver.
>> +                      */
>> +                     mode |= ATMEL_US_USMODE_NORMAL;
>
> You still need the case where HWHS is impossible and there are no gpio
> configured. You need to inform userspace that the configuration was not
> applied instead of silently ignoring the error.

Could you explain which case it is ?
The only one I can see is when there's no GPIO declared for RTS/CTS
AND, there's no pin muxed for RTS/CTS either.

Have you got another example in mind ?


>
>>       } else {
>>               /* RS232 without hadware handshake or controlled by GPIOs */
>>               mode |= ATMEL_US_USMODE_NORMAL;
>
> --
> Alexandre Belloni, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com



-- 
for me, ck means con kolivas and not calvin klein... does it mean I'm a geek ?