Re: [PATCH 1/3] serdev: ttyport: make use of tty_kopen_exclusive

Marco Felsch
2024-08-19T12:24:06Z

On 24-08-19, Jiri Slaby wrote:
> On 19. 08. 24, 12:19, Marco Felsch wrote:
> > Hi,
> >
> > sorry for not replying earlier.
> >
> > On 24-08-08, Jiri Slaby wrote:
> > > On 07. 08. 24, 16:08, Marco Felsch wrote:
> > > > The purpose of serdev is to provide kernel drivers for particular serial
> > > > device, serdev-ttyport is no exception here. Make use of the
> > > > tty_kopen_exclusive() funciton to mark this tty device as kernel
> > > > internal device.
> > > >
> > > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > > > ---
> > > > drivers/tty/serdev/serdev-ttyport.c | 9 ++++++---
> > > > 1 file changed, 6 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serdev/serdev-ttyport.c
> > > > index 3d7ae7fa5018..94c43d25ddbe 100644
> > > > --- a/drivers/tty/serdev/serdev-ttyport.c
> > > > +++ b/drivers/tty/serdev/serdev-ttyport.c
> > > > @@ -103,11 +103,14 @@ static int ttyport_write_room(struct serdev_controller *ctrl)
> > > > static int ttyport_open(struct serdev_controller *ctrl)
> > > > {
> > > > struct serport *serport = serdev_controller_get_drvdata(ctrl);
> > > > + struct tty_driver *tty_drv = serport->tty_drv;
> > > > struct tty_struct *tty;
> > > > struct ktermios ktermios;
> > > > + dev_t dev;
> > > > int ret;
> > > > - tty = tty_init_dev(serport->tty_drv, serport->tty_idx);
> > > > + dev = MKDEV(tty_drv->major, tty_drv->minor_start + serport->tty_idx);
> > > > + tty = tty_kopen_exclusive(dev);
> > >
> > > I believe that the now added tty_lookup_driver() has negligible impact in
> > > this anyway slow path, right?
> >
> > Can you please elaborate a bit more? I don't see how the
> > tty_lookup_driver() is involved in the serdev-ctrl open path anyway.
>
> It's called now in of tty_kopen_exclusive()->tty_kopen().
> (tty_lookup_driver() is the major difference between the raw tty_init_dev()
> and tty_kopen_exclusive().)

Okay now I get the "now added tty_lookup_driver()" statement, sorry.
Yes, I believe that this is negligible. The main difference for me was
that the tty_port_set_kopened() is set accordingly which which is
important to not trigger warnings during the release path.

Regards,
Marco

>
> --
> js
> suse labs
>
>