Re: [PATCH v2] serial: uart: add hw flow control support configuration

[Murali Karicheri]

On 08/07/2014 11:29 AM, Peter Hurley wrote:
> On 05/01/2014 03:04 PM, Murali Karicheri 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.
> >
> > 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/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)) {
> Why is a modem status interrupt being generated for DCTS
> if autoflow control is enabled?
>
> This should be:
>
> 	WARN_ON_ONCE(uport->flags&  UPF_HARD_FLOW);
>
> to indicate a mis-configured driver/device.
This patch is already merged to the upstream branch and if you see any 
issue, please
post a patch for review.

Murali
> >   		if (tty->hw_stopped) {
> >   			if (status) {
> >   				tty->hw_stopped = 0;

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