[PATCH] tty/serial: at91: fix hardware handshake on Atmel platforms

[Alexandre Belloni]

Hi,

On 25/10/2016 at 18:11:35 +0200, Richard Genoud wrote :
> commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
> hardware handshake is enabled"), despite its title, broke hardware
> handshake on *every* Atmel platforms.
> 
> The only one partially working is the SAMA5D2.
> 

[...]

> Changes since v4:
>  - the mctrl_gpio_use_rtscts() is gone since it was atmel_serial
>  specific. (so patch 1 is gone)
>  - patches 2 and 3 have been merged together since it didn't make
>  a lot of sense to correct the GPIO case in one separate patch.
>  - ATMEL_US_USMODE_HWHS is now unset for platform with PDC
> 
> Changes since v3:
>  - remove superfluous #include <linux/err.h> (thanks to Uwe)
>  - rebase on next-20160930
> 
> Changes since v2:
>  - remove IS_ERR_OR_NULL() test in patch 1/3 as Uwe suggested.
>  - fix typos in patch 2/3
>  - rebase on next-20160927
>  - simplify the logic in patch 3/3.
> 
> Changes since v1:
>  - Correct patch 1 with the error found by kbuild.
>  - Add Alexandre's Acked-by on patch 2
>  - Rewrite patch 3 logic in the light of the on-going discussion
>    with Cyrille and Alexandre.
> 

The changelog has to go after the --- marker.

> * the list may not be exhaustive
> 
> Signed-off-by: Richard Genoud <richard.genoud at gmail.com>

Acked-by: Alexandre Belloni <alexandre.belloni at free-electrons.com>

> ---
>  drivers/tty/serial/atmel_serial.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
>  I think this should go in the stable tree since it fixes the flow
>  control broken since v4.0.
>  But It won't compile on versions before 4.9rc1 because:
>  function atmel_use_fifo was introduced in 4.4.12 / 4.7
>  variable atmel_port was introduced in 4.9rc1
> 
>  That's why I didn't add the Cc stable in the email body.
> 
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index fd8aa1f4ba78..2c7c45904ba7 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -2132,11 +2132,28 @@ 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.
> +			 * 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;
> +		} else {
> +			/*
> +			 * For platforms without FIFO, the flow control is
> +			 * handled by the driver.
> +			 */
> +			mode |= ATMEL_US_USMODE_NORMAL;
>  		}
>  	} else {
>  		/* RS232 without hadware handshake */

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com