2016-10-27 20:02 GMT+02:00 Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>:
> Hello Richard,
>
> On Thu, Oct 27, 2016 at 06:04:06PM +0200, Richard Genoud wrote:
>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> index fd8aa1f4ba78..168b10cad47b 100644
>> --- a/drivers/tty/serial/atmel_serial.c
>> +++ b/drivers/tty/serial/atmel_serial.c
>> @@ -2132,11 +2132,29 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>> mode |= ATMEL_US_USMODE_RS485;
>> } else if (termios->c_cflag & CRTSCTS) {
>> /* RS232 with hardware handshake (RTS/CTS) */
>> - 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_fifo(port) &&
>> + !mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS)) {
>> + /*
>> + * with ATMEL_US_USMODE_HWHS set, the controller will
>> + * be able to drive the RTS pin high/low when the RX
>> + * FIFO is above RXFTHRES/below RXFTHRES2.
>> + * It will also disable the transmitter when the CTS
>> + * pin is high.
>> + * This mode is not activated if CTS pin is a GPIO
>> + * because in this case, the transmitter is always
>> + * disabled (there must be an internal pull-up
>> + * responsible for this behaviour).
>> + * If the RTS pin is a GPIO, the controller won't be
>> + * able to drive it according to the FIFO thresholds,
>> + * but it will be handled by the driver.
>> + */
>> mode |= ATMEL_US_USMODE_HWHS;
>
> You use
>
> !mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS)
>
> as indicator that the cts mode of the respective pin is used. Is this
> reliable? (It's not if there are machines that don't use CTS, neither as
> gpio nor using the hardware function.) Maybe this needs a dt property to
> indicate that there is no (hw)handshaking available?
I used that to filter-out the case where CTS is a GPIO.
Now, for the machines that don't use CTS neither as GPIO nor using the
hardware function, it's a whole different story, beyond the scope of this patch.
And like you said, a DT property could be useful to handle this case.
( It's a little bit like if there was an RS232 cable with just TX/RX/GND, but
this will be way harder to detect :) )
Anyway, patches are welcome to handle that, but I don't think it belongs
in this one.
>> + } else {
>> + ...
>> }
>
> Best regards
> Uwe
>
regards,
Richard
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