linux-kernel - Re: [PATCH 2/3] tty/serial: at91: fix hardware handshake with GPIOs

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Message-ID: <20160907174309.4xyd276rwbzd57sb@piout.net>
Date:   Wed, 7 Sep 2016 19:43:09 +0200
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Richard Genoud <richard.genoud@...il.com>
Cc:     Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Nicolas Ferre <nicolas.ferre@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/3] tty/serial: at91: fix hardware handshake with GPIOs

On 07/09/2016 at 18:13:23 +0200, Richard Genoud wrote :
> Commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
> hardware handshake is enabled") broke the hardware handshake when GPIOs
> where used.
> 
> Hardware handshake with GPIOs used to work before this commit because
> the CRTSCTS flag (termios->c_cflag) was set, but not the
> ATMEL_US_USMODE_HWHS flag (controller register) ; so hardware handshake
> enabled, but not handled by the controller.
> 
> This commit restores this behaviour.
> 
> NB: -stable is not Cced because it doesn't cleanly apply on 4.1+
> and it will also need previous commit:
> "serial: mctrl_gpio: implement mctrl_gpio_use_rtscts"
> 
> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
> Fixes: 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when hardware handshake is enabled")
Acked-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>

> ---
>  drivers/tty/serial/atmel_serial.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 2eaa18ddef61..e9b4fbf88c2d 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -2025,6 +2025,7 @@ static void atmel_serial_pm(struct uart_port *port, unsigned int state,
>  static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>  			      struct ktermios *old)
>  {
> +	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
>  	unsigned long flags;
>  	unsigned int old_mode, mode, imr, quot, baud;
>  
> @@ -2126,8 +2127,12 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>  		atmel_uart_writel(port, ATMEL_US_TTGR,
>  				  port->rs485.delay_rts_after_send);
>  		mode |= ATMEL_US_USMODE_RS485;
> -	} else if (termios->c_cflag & CRTSCTS) {
> -		/* RS232 with hardware handshake (RTS/CTS) */
> +	} else if ((termios->c_cflag & CRTSCTS) &&
> +		   !mctrl_gpio_use_rtscts(atmel_port->gpios)) {
> +		/*
> +		 * RS232 with hardware handshake (RTS/CTS)
> +		 * handled by the controller.
> +		 */
>  		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;
> @@ -2135,7 +2140,7 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>  			mode |= ATMEL_US_USMODE_HWHS;
>  		}
>  	} else {
> -		/* RS232 without hadware handshake */
> +		/* 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