linux-kernel - Re: [PATCH v6 2/4] tty: rename tty_kopen() and add new function tty_kopen

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Date:   Tue, 25 Feb 2020 10:05:51 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Johan Hovold <johan@...nel.org>
Cc:     kernel@...gutronix.de, linux-serial@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Dan Murphy <dmurphy@...com>,
        Pavel Machek <pavel@....cz>, Jiri Slaby <jslaby@...e.com>,
        linux-leds@...r.kernel.org,
        Jacek Anaszewski <jacek.anaszewski@...il.com>
Subject: Re: [PATCH v6 2/4] tty: rename tty_kopen() and add new function
 tty_kopen_shared()

On Tue, Feb 25, 2020 at 09:55:03AM +0100, Johan Hovold wrote:
> On Thu, Feb 20, 2020 at 12:04:27PM +0100, Uwe Kleine-König wrote:
> > Ah I think I see. tty_driver_lookup_tty() might return NULL which for
> > the trigger driver indicates that tty_kopen_shared should be retried,
> > right?
> 
> I'm not sure how best to handle this, but yes, your trigger can only be
> enabled while the port is open currently. And no error is returned to a
> user trying to enable the trigger before it has been opened.
> 
> But regardless of the error reporting, I don't think failing when the
> port isn't open is the right thing to do as as this makes the interface
> rather useless since you cannot enable a trigger from for example a udev
> rule.
> 
> If this approach is to be used at all, it seems you may need to allocate
> the struct tty when the trigger is enabled. And make sure you don't mess
> up some other assumption in tty core...

My idea is instead to retry opening the device later. At least this
sounds easier.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |