RE: [PATCH] serial: uart: add hw flow control support configuration

[Karicheri, Muralidharan]

>-----Original Message-----
>From: Karicheri, Muralidharan
>Sent: Friday, April 11, 2014 3:18 PM
>To: devicetree@xxxxxxxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>linux-serial@xxxxxxxxxxxxxxx
>Cc: Balbi, Felipe; Karicheri, Muralidharan; Rob Herring; Mark Rutland; Ian Campbell;
>Kumar Gala; Randy Dunlap; Greg Kroah-Hartman; Jiri Slaby
>Subject: [PATCH] serial: uart: add hw flow control support configuration
>
>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.
>
>CC: Rob Herring <robh+dt@xxxxxxxxxx>
>CC: Pawel Moll <pawel.moll@xxxxxxx>
>CC: Mark Rutland <mark.rutland@xxxxxxx>
>CC: Ian Campbell <ijc+devicetree@xxxxxxxxxxxxxx>
>CC: Kumar Gala <galak@xxxxxxxxxxxxxx>
>CC: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
>CC: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>CC: Jiri Slaby <jslaby@xxxxxxx>
>
>Signed-off-by: Murali Karicheri <m-karicheri2@xxxxxx>
>---
> .../devicetree/bindings/serial/of-serial.txt       |    2 ++
> 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, 19 insertions(+), 5 deletions(-)
>
>diff --git a/Documentation/devicetree/bindings/serial/of-serial.txt
>b/Documentation/devicetree/bindings/serial/of-serial.txt
>index 1928a3e..123de01 100644
>--- a/Documentation/devicetree/bindings/serial/of-serial.txt
>+++ b/Documentation/devicetree/bindings/serial/of-serial.txt
>@@ -37,6 +37,8 @@ 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.
>+- hw-flow-control: this enables pure hw flow control and no software
>+  intervention needed.
>
> Example:
>
>diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
>index 81f909c..6b1b868 100644
>--- a/drivers/tty/serial/8250/8250_core.c
>+++ b/drivers/tty/serial/8250/8250_core.c
>@@ -2338,9 +2338,11 @@ 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
>9924660..1a5f528 100644
>--- a/drivers/tty/serial/of_serial.c
>+++ b/drivers/tty/serial/of_serial.c
>@@ -182,6 +182,10 @@ 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,
>+					  "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 2cf5649..16e3615 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;
>@@ -2768,7 +2772,9 @@ 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;
>--
>1.7.9.5

Can this be queued up for merge if looks good?

Murali Karicheri
Linux Kernel, Software Development


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