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.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
CC: Rob Herring <robh+dt@kernel.org>
CC: Pawel Moll <pawel.moll@arm.com>
CC: Mark Rutland <mark.rutland@arm.com>
CC: Ian Campbell <ijc+devicetree@hellion.org.uk>
CC: Kumar Gala <galak@codeaurora.org>
CC: Randy Dunlap <rdunlap@infradead.org>
CC: Jiri Slaby <jslaby@suse.cz>
CC: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/devicetree/bindings/serial/of-serial.txt b/Documentation/devicetree/bindings/serial/of-serial.txt
index 1928a3e83cd0413262de68c036242cb0b92b08fa..77054772a8f4fe46cb57ba461544e8de606d337c 100644 (file)
--- 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 111ee8acb07ea437cb145d3a43f48c94d11a2494..65556fc57d5606259d343f458d367e50660f8f1d 100644 (file)
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -2333,9 +2333,11 @@ 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 99246606a256b71cbef9272b1402afc4bdcf1009..77ec6a147522394423c7cf7478402d931edd5ba9 100644 (file)
--- 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,
+                                         "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 9a01ee4dda6df1fc1427e761a0b015d455cb12fb..fbf6c5ad222f55015d79598ff4295723dd396456 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -174,8 +174,12 @@ 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;
@@ -2775,7 +2779,9 @@ 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;