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

[Rob Herring]

On Thu, Jan 19, 2017 at 9:05 AM, Rob Herring <robh@xxxxxxxxxx> wrote:
> On Thu, Jan 19, 2017 at 7:37 AM, Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>> On Mon, Jan 16, 2017 at 04:54:29PM -0600, Rob Herring wrote:
>>> From: Alan Cox <alan@xxxxxxxxxxxxxxx>
>>>
>>> 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@xxxxxxxxxxxxxxx>
>>> Reviewed-By: Sebastian Reichel <sre@xxxxxxxxxx>
>>> ---
>>> 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.

Oh, I see you applied the 1st patch. Thanks. If you want to apply this
one now here's my S-o-B:

Signed-off-by: Rob Herring <robh@xxxxxxxxxx>

Patches 3 and 4 can be applied too.

For patch 5, I'd really like someone with more tty knowledge to comment on.

Rob