linux-kernel - Re: [PATCH v2 2/9] tty_port: allow a port to be opened with a tty that has no file handle

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Date:   Thu, 19 Jan 2017 09:05:38 -0600
From:   Rob Herring <robh@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sebastian Reichel <sre@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Dr . H . Nikolaus Schaller" <hns@...delico.com>,
        Peter Hurley <peter@...leysoftware.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Loic Poulain <loic.poulain@...el.com>,
        Pavel Machek <pavel@....cz>, NeilBrown <neil@...wn.name>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH v2 2/9] tty_port: allow a port to be opened with a tty
 that has no file handle

On Thu, Jan 19, 2017 at 7:37 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Mon, Jan 16, 2017 at 04:54:29PM -0600, Rob Herring wrote:
>> From: Alan Cox <alan@...ux.intel.com>
>>
>> Let us create tty objects entirely in kernel space. Untested proposal to
>> show why all the ideas around rewriting half the uart stack are not needed.
>>
>> With this a kernel created non file backed tty object could be used to handle
>> data, and set terminal modes. Not all ldiscs can cope with this as N_TTY in
>> particular has to work back to the fs/tty layer.
>>
>> The tty_port code is however otherwise clean of file handles as far as I can
>> tell as is the low level tty port write path used by the ldisc, the
>> configuration low level interfaces and most of the ldiscs.
>>
>> Currently you don't have any exposure to see tty hangups because those are
>> built around the file layer. However a) it's a fixed port so you probably
>> don't care about that b) if you do we can add a callback and c) you almost
>> certainly don't want the userspace tear down/rebuild behaviour anyway.
>>
>> This should however be sufficient if we wanted for example to enumerate all
>> the bluetooth bound fixed ports via ACPI and make them directly available.
>> It doesn't deal with the case of a user opening a port that's also kernel
>> opened and that would need some locking out (so it returned EBUSY if bound
>> to a kernel device of some kind). That needs resolving along with how you
>> "up" or "down" your new bluetooth device, or enumerate it while providing
>> the existing tty API to avoid regressions (and to debug).
>>
>> Alan
>> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>> Reviewed-By: Sebastian Reichel <sre@...nel.org>
>> ---
>> Alan, Need your SoB here.
>
> Rob, as this patch is flowing through you, I need your signed-off-by as
> well if I am to take it.

Right. I've added both for the next version.

Rob