On Wed, 2013-02-13 at 14:32 -0500, Peter Hurley wrote:
> On Wed, 2013-02-13 at 18:27 +0100, Johan Hovold wrote:
> > Move HUPCL handling to port shutdown so that DTR/RTS is dropped also on
> > hang up.
> >
> > Currently a hung up port will return immediately from
> > tty_port_close_start leaving DTR/RTS unchanged.
> > ---
> > drivers/tty/tty_port.c | 22 ++++++++++++----------
> > 1 file changed, 12 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
> > index 57a061e..ffe3689 100644
> > --- a/drivers/tty/tty_port.c
> > +++ b/drivers/tty/tty_port.c
> > @@ -198,11 +198,20 @@ EXPORT_SYMBOL(tty_port_tty_set);
> >
> > static void tty_port_shutdown(struct tty_port *port)
> > {
> > + struct tty_struct *tty = port->tty;
> > +
> > mutex_lock(&port->mutex);
> > if (port->console)
> > goto out;
> >
> > if (test_and_clear_bit(ASYNCB_INITIALIZED, &port->flags)) {
> > + /*
> > + * Drop DTR/RTS if HUPCL is set. This causes any attached
> > + * modem to hang up the line.
> > + */
> > + if (!tty || tty->termios.c_cflag & HUPCL)
> > + tty_port_lower_dtr_rts(port);
> > +
>
> port->ops->shutdown() requires the hardware to reset anyway, including
> the DTR/RTS state.
Ok, after reviewing this further, I like this more.
For one, there is more flexibility for tty drivers that have a custom
close() routine (ie, one that doesn't call tty_port_close()). At the
same time, every call site of tty_port_close_start() needs to be checked
to ensure it does not assume (or does not require) DTR to be dropped:
char/pcmcia/synclink_cs.c: if (tty_port_close_start(port, tty, filp) == 0)
tty/synclinkmp.c: if (tty_port_close_start(&info->port, tty, filp) == 0)
tty/rocket.c: if (tty_port_close_start(port, tty, filp) == 0)
tty/amiserial.c: if (tty_port_close_start(port, tty, filp) == 0)
tty/n_gsm.c: if (tty_port_close_start(&dlci->port, tty, filp) == 0)
tty/mxser.c: if (tty_port_close_start(port, tty, filp) == 0)
tty/synclink_gt.c: if (tty_port_close_start(&info->port, tty, filp) == 0)
tty/serial/serial_core.c: if (tty_port_close_start(port, tty, filp) == 0)
tty/synclink.c: if (tty_port_close_start(&info->port, tty, filp) == 0)
In the case of the serial core, this actually fixes the code excerpt
below where tty_port_close_start() prematurely drops DTR before the uart
can stop_rx() or wait_until_sent().
static void uart_close(struct tty_struct *tty, struct file *filp)
{
struct uart_state *state = tty->driver_data;
struct tty_port *port;
struct uart_port *uport;
unsigned long flags;
if (!state)
return;
uport = state->uart_port;
port = &state->port;
pr_debug("uart_close(%d) called\n", uport->line);
if (tty_port_close_start(port, tty, filp) == 0)
return;
/*
* At this point, we stop accepting input. To do this, we
* disable the receive line status interrupts.
*/
if (port->flags & ASYNC_INITIALIZED) {
unsigned long flags;
spin_lock_irqsave(&uport->lock, flags);
uport->ops->stop_rx(uport);
spin_unlock_irqrestore(&uport->lock, flags);
/*
* Before we drop DTR, make sure the UART transmitter
* has completely drained; this is especially
* important if there is a transmit FIFO!
*/
uart_wait_until_sent(tty, uport->timeout);
}
mutex_lock(&port->mutex);
uart_shutdown(tty, state);
uart_flush_buffer(tty);
Regards,
Peter Hurley
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