On Thu, May 1, 2014 at 1:04 PM, Murali Karicheri <m-karicheri2@xxxxxx> wrote: > 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. ubuntu@hwflow:~$ sudo stty -a --file /dev/ttyS0 |tr ' ' '\n' | grep crtscts crtscts ubuntu@hwflow:~$ ls /proc/device-tree/soc/serial@1c021000/has-hw-flow-control /proc/device-tree/soc/serial@1c021000/has-hw-flow-control ubuntu@hwflow:~$ python Python 2.7.6 (default, Mar 22 2014, 22:58:30) [GCC 4.8.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> UPF_HARDWARE_FLOW = 1 << 21 >>> if 0xB9200000 & UPF_HARDWARE_FLOW: ... print "OK" ... OK Hope that's a reasonable test case. Test fails when booted w/o has-hw-flow-control attribute. Tested-by: dann frazier <dann.frazier@xxxxxxxxxxxxx> > > Signed-off-by: Murali Karicheri <m-karicheri2@xxxxxx> > > 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> > CC: Santosh Shilimkar <santosh.shilimkar@xxxxxx> > --- > .../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 0e1bf88..b69aff2 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..77ec6a1 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, > + "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 b68550d..851707a 100644 > --- 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; > @@ -2772,7 +2776,9 @@ 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 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html