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

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Message-ID: <20240819101946.cf7x7xecdn2pfa4t@pengutronix.de>
Date: Mon, 19 Aug 2024 12:19:46 +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

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.

Regards,
  Marco