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

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Message-ID: <dc936358-a718-4f1c-a2a6-695bbae1d2ec@kernel.org>
Date: Mon, 19 Aug 2024 12:42:09 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Marco Felsch <m.felsch@...gutronix.de>
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 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().)

-- 
js
suse labs