[Acked] [PATCH Trusty SRU] serial: uart: add hw flow control support configuration

[Andy Whitcroft]

On Mon, Jun 09, 2014 at 04:57:22PM -0600, Dann Frazier wrote:
> Also not in utopic, but utopic should automatically pick it up when we
> migrate it to 3.16.

> From 667c1c27e4c0b191ec0e210418b45043c68de1ee Mon Sep 17 00:00:00 2001
> From: Murali Karicheri <m-karicheri2 at ti.com>
> Date: Thu, 1 May 2014 15:04:53 -0400
> Subject: [PATCH] serial: uart: add hw flow control support configuration
> 
> BugLink: https://bugs.launchpad.net/bugs/1328295
> 
> commit 06aa82e498c144c7784a6f3d3b55458b272d6146 upstream.
> 
> 8250 uart driver currently supports only software assisted hw flow
> control. The software assisted hw flow control maintains a hw_stopped
> flag in the tty structure to stop and start transmission and use modem
> status interrupt for the event to drive the handshake signals. This is
> not needed if hw has flow control capabilities. This patch adds a
> DT attribute for enabling hw flow control for a uart port. Also skip
> stop and start if this flag is present in flag field of the port
> structure.
> 
> Signed-off-by: Murali Karicheri <m-karicheri2 at ti.com>
> CC: Rob Herring <robh+dt at kernel.org>
> CC: Pawel Moll <pawel.moll at arm.com>
> CC: Mark Rutland <mark.rutland at arm.com>
> CC: Ian Campbell <ijc+devicetree at hellion.org.uk>
> CC: Kumar Gala <galak at codeaurora.org>
> CC: Randy Dunlap <rdunlap at infradead.org>
> CC: Jiri Slaby <jslaby at suse.cz>
> CC: Santosh Shilimkar <santosh.shilimkar at ti.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Signed-off-by: dann frazier <dann.frazier at canonical.com>
> ---
>  Documentation/devicetree/bindings/serial/of-serial.txt |  1 +
>  drivers/tty/serial/8250/8250_core.c                    |  6 ++++--
>  drivers/tty/serial/of_serial.c                         |  4 ++++
>  drivers/tty/serial/serial_core.c                       | 12 +++++++++---
>  4 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/serial/of-serial.txt b/Documentation/devicetree/bindings/serial/of-serial.txt
> index 1928a3e..7705477 100644
> --- a/Documentation/devicetree/bindings/serial/of-serial.txt
> +++ b/Documentation/devicetree/bindings/serial/of-serial.txt
> @@ -37,6 +37,7 @@ Optional properties:
>  - auto-flow-control: one way to enable automatic flow control support. The
>    driver is allowed to detect support for the capability even without this
>    property.
> +- has-hw-flow-control: the hardware has flow control capability.
>  
>  Example:
>  
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 61ecd70..49fc41ec 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -2334,9 +2334,11 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  	 * the trigger, or the MCR RTS bit is cleared.  In the case where
>  	 * the remote UART is not using CTS auto flow control, we must
>  	 * have sufficient FIFO entries for the latency of the remote
> -	 * UART to respond.  IOW, at least 32 bytes of FIFO.
> +	 * UART to respond.  IOW, at least 32 bytes of FIFO. Also enable
> +	 * AFE if hw flow control is supported
>  	 */
> -	if (up->capabilities & UART_CAP_AFE && port->fifosize >= 32) {
> +	if ((up->capabilities & UART_CAP_AFE && (port->fifosize >= 32)) ||
> +	    (port->flags & UPF_HARD_FLOW)) {
>  		up->mcr &= ~UART_MCR_AFE;
>  		if (termios->c_cflag & CRTSCTS)
>  			up->mcr |= UART_MCR_AFE;
> diff --git a/drivers/tty/serial/of_serial.c b/drivers/tty/serial/of_serial.c
> index 2caf9c6..a41d161 100644
> --- a/drivers/tty/serial/of_serial.c
> +++ b/drivers/tty/serial/of_serial.c
> @@ -183,6 +183,10 @@ static int of_platform_serial_probe(struct platform_device *ofdev)
>  					  "auto-flow-control"))
>  			port8250.capabilities |= UART_CAP_AFE;
>  
> +		if (of_property_read_bool(ofdev->dev.of_node,
> +					  "has-hw-flow-control"))
> +			port8250.port.flags |= UPF_HARD_FLOW;
> +
>  		ret = serial8250_register_8250_port(&port8250);
>  		break;
>  	}
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 0f02351..a91af71 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -170,8 +170,12 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
>  			if (tty->termios.c_cflag & CBAUD)
>  				uart_set_mctrl(uport, TIOCM_RTS | TIOCM_DTR);
>  		}
> -
> -		if (tty_port_cts_enabled(port)) {
> +		/*
> +		 * if hw support flow control without software intervention,
> +		 * then skip the below check
> +		 */
> +		if (tty_port_cts_enabled(port) &&
> +		    !(uport->flags & UPF_HARD_FLOW)) {
>  			spin_lock_irq(&uport->lock);
>  			if (!(uport->ops->get_mctrl(uport) & TIOCM_CTS))
>  				tty->hw_stopped = 1;
> @@ -2754,7 +2758,9 @@ void uart_handle_cts_change(struct uart_port *uport, unsigned int status)
>  
>  	uport->icount.cts++;
>  
> -	if (tty_port_cts_enabled(port)) {
> +	/* skip below code if the hw flow control is supported */
> +	if (tty_port_cts_enabled(port) &&
> +	    !(uport->flags & UPF_HARD_FLOW)) {
>  		if (tty->hw_stopped) {
>  			if (status) {
>  				tty->hw_stopped = 0;
> -- 
> 2.0.0
> 

Is an upstrea cherry-pick, looks to do what is claimed, is device
specific and only triggered by a device tree flag so low regression
potential.  Therefore:

Acked-by: Andy Whitcroft <apw at canonical.com>

-apw