[1/5] tty: add port flag to suppress ready signalling on open

Add a NORDY port flag to suppress raising the modem-control lines on
open to signal DTE readiness.

This can be used to implement a NORDY termios control flag to complement
HUPCL, which controls lowering of the modem-control lines on final
close.

Initially drivers can export the flag through sysfs, which also allows
control over the lines on first open.

This can be use to prevent undesirable side-effects on open for
applications where the DTR and RTS lines are used for non-standard
purposes such as generating power-on and reset pulses.

Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/tty/tty_port.c |  2 +-
 include/linux/tty.h    | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

> Add a NORDY port flag to suppress raising the modem-control lines on
> open to signal DTE readiness.
>
> This can be used to implement a NORDY termios control flag to complement
> HUPCL, which controls lowering of the modem-control lines on final
> close.
>
> Initially drivers can export the flag through sysfs, which also allows
> control over the lines on first open.
>
> This can be use to prevent undesirable side-effects on open for
> applications where the DTR and RTS lines are used for non-standard
> purposes such as generating power-on and reset pulses.
>
> Signed-off-by: Johan Hovold <johan@kernel.org>

Reviewed-by: Mychaela N. Falconia <falcon@freecalypso.org>

On 30. 11. 20, 16:37, Johan Hovold wrote:
> --- a/include/linux/tty.h
> +++ b/include/linux/tty.h
> @@ -683,6 +684,19 @@ static inline void tty_port_set_kopened(struct tty_port *port, bool val)
>   		clear_bit(TTY_PORT_KOPENED, &port->iflags);
>   }
>   
> +static inline bool tty_port_nordy(struct tty_port *port)

port can be const here.

> +{
> +	return test_bit(TTY_PORT_NORDY, &port->iflags);
> +}
> +
> +static inline void tty_port_set_nordy(struct tty_port *port, bool val)
> +{
> +	if (val)
> +		set_bit(TTY_PORT_NORDY, &port->iflags);
> +	else
> +		clear_bit(TTY_PORT_NORDY, &port->iflags);

We have assign_bit() for these cases these days.

thanks,

On 11/30/20, Jiri Slaby <jirislaby@kernel.org> wrote:
> port can be const here.
> [...]
> We have assign_bit() for these cases these days.

Johan's patch adding test and set accessor inline functions for the
new flag follows the style of the existing accessor inline functions
for previously existing flags, for the sake of consistency. If we are
going to use the new style (const for test functions, assign_bit() for
set functions) for the new flag, then we should also change all
existing ones for consistency. In terms of patch splitting, would it
be most kosher to have one patch that updates the style of existing
accessor inline functions, and then the interesting patch that adds
the new flag?

M~

On 01. 12. 20, 8:09, Mychaela Falconia wrote:
> On 11/30/20, Jiri Slaby <jirislaby@kernel.org> wrote:

>> port can be const here.

>> [...]

>> We have assign_bit() for these cases these days.

> 

> Johan's patch adding test and set accessor inline functions for the

> new flag follows the style of the existing accessor inline functions

> for previously existing flags, for the sake of consistency. If we are

> going to use the new style (const for test functions, assign_bit() for

> set functions) for the new flag, then we should also change all

> existing ones for consistency. In terms of patch splitting, would it

> be most kosher to have one patch that updates the style of existing

> accessor inline functions, and then the interesting patch that adds

> the new flag?


Yes. Or the other way around. Add this new using const+assign_bit and 
convert the rest on the top of the series.

thanks,
-- 
js

On Tue, Dec 01, 2020 at 06:49:07AM +0100, Jiri Slaby wrote:
> On 30. 11. 20, 16:37, Johan Hovold wrote:
> > --- a/include/linux/tty.h
> > +++ b/include/linux/tty.h
> > @@ -683,6 +684,19 @@ static inline void tty_port_set_kopened(struct tty_port *port, bool val)
> >   		clear_bit(TTY_PORT_KOPENED, &port->iflags);
> >   }
> >   
> > +static inline bool tty_port_nordy(struct tty_port *port)
> 
> port can be const here.

Sure, but see below.

> > +{
> > +	return test_bit(TTY_PORT_NORDY, &port->iflags);
> > +}
> > +
> > +static inline void tty_port_set_nordy(struct tty_port *port, bool val)
> > +{
> > +	if (val)
> > +		set_bit(TTY_PORT_NORDY, &port->iflags);
> > +	else
> > +		clear_bit(TTY_PORT_NORDY, &port->iflags);
> 
> We have assign_bit() for these cases these days.

Right, but for both your comments this follows the pattern used by the
other port-flag helpers.

I can add a preparatory patch updating the current helpers, but I don't
think this needs to be a blocker.

Johan