linux-kernel - Re: [PATCH 1/3] serdev: ttyport: make use of tty_kopen

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Message-ID: <20240819122356.rh2f6ldpauvxhgui@pengutronix.de>
Date: Mon, 19 Aug 2024 14:23:56 +0200
From: Marco Felsch <m.felsch@...gutronix.de>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Rob Herring <robh@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Johan Hovold <johan@...nel.org>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 1/3] serdev: ttyport: make use of tty_kopen_exclusive

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@...gutronix.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
> 
>