linux-kernel - Re: [PATCH 0/9] tty: tty_struct dependency clean-ups

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Date:   Mon, 12 Sep 2016 12:46:55 +0100
From:   One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:     Rob Herring <robh@...nel.org>
Cc:     Alan Cox <alan@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Hurley <peter@...leysoftware.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH 0/9] tty: tty_struct dependency clean-ups

On Sun, 11 Sep 2016 22:05:07 -0500
Rob Herring <robh@...nel.org> wrote:

> On Sun, Sep 11, 2016 at 4:14 PM, One Thousand Gnomes
> <gnomes@...rguk.ukuu.org.uk> wrote:
> > On Fri,  9 Sep 2016 17:37:01 -0500
> > Rob Herring <robh@...nel.org> wrote:
> >  
> >> This patch series removes or prepares to remove some of the dependencies
> >> on tty_struct within tty_port drivers. This will allow using tty_ports
> >> directly for so called UART slave devices.  
> >
> > You can create a tty_struct kernel side with the two tiny changes I
> > posted before. Why do you want to do invasive tree wide changes when you
> > can do simple ones ?  
> 
> Well, I don't want to do invasive changes, but I thought the idea was
> to use tty_port struct without a tty_struct.

I posted some tiny patches to break the file/tty requirement in the base
tty code for comment a while ago and they were very tiny for most ldiscs
(n_tty unsurprisingly wouldn't work this way but does anyone need kernel
mode n_tty ?)

Moving termios into the tty_port is IMHO a good thing to do whichever
approach is taken.

> I was planning to keep termios out of tty_port and make clients of
> tty_port carry it if for nothing else not quite understanding all the
> details around the lifetime, init and locking of it. If there's always
> a tty_struct then there's not much point moving it other than which
> struct makes more sense. But that would cause some churn.

The termios lifetime is the lifetime of the port, although it may get
reset at some times.

Alan