The user-settable knob, low_latency, has been the source of
several BUG reports which stem from flush_to_ldisc() running
in interrupt context. Since 3.12, which added several sleeping
locks (termios_rwsem and buf->lock) to the input processing path,
the frequency of these BUG reports has increased.

Note that changes in 3.12 did not introduce this regression;
sleeping locks were first added to the input processing path
with the removal of the BKL from N_TTY in commit
a88a69c9,
'n_tty: Fix loss of echoed characters and remove bkl from n_tty'
and later in commit 38db8979,
'tty: throttling race fix'. Since those changes, executing
flush_to_ldisc() in interrupt_context (ie, low_latency set), is unsafe.

However, since most devices do not validate if the low_latency
setting is appropriate for the context (process or interrupt) in
which they receive data, some reports are due to misconfiguration.
Further, serial dma devices for which dma fails, resort to
interrupt receiving as a backup without resetting low_latency.

Historically, low_latency was used to force wake-up the reading
process rather than wait for the next scheduler tick. The
effect was to trim multiple milliseconds of latency from
when the process would receive new data.

Recent tests [1] have shown that the reading process now receives
data with only 10's of microseconds latency without low_latency set.

Remove the low_latency rx steering from tty_flip_buffer_push();
however, leave the knob as an optional hint to drivers that can
tune their rx fifos and such like. Cleanup stale code comments
regarding low_latency.

[1] https://lkml.org/lkml/2014/2/20/434

"Yay.. thats an annoying historical pain in the butt gone."
	-- Alan Cox
Reported-by: NBeat Bolli <bbolli@ewanet.ch>
Reported-by: NPavel Roskin <proski@gnu.org>
Acked-by: NDavid Sterba <dsterba@suse.cz>
Cc: Grant Edwards <grant.b.edwards@gmail.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Hal Murray <murray+fedora@ip-64-139-1-69.sjc.megapath.net>
Cc: <stable@vger.kernel.org> # 3.12.x+
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

None of these files are actually using any __init type directives
and hence don't need to include <linux/init.h>.  Most are just a
left over from __devinit and __cpuinit removal, or simply due to
code getting copied from one driver to the next.
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Now, we start converting tty buffer functions to actually use
tty_port. This will allow us to get rid of the need of tty in many
call sites. Only tty_port will needed and hence no more
tty_port_tty_get in those paths.

Now, the one where most of tty_port_tty_get gets removed:
tty_flip_buffer_push.

IOW we also closed all the races in drivers not using tty_port_tty_get
at all yet.

Also we move tty_flip_buffer_push declaration from include/linux/tty.h
to include/linux/tty_flip.h to all others while we are changing it
anyway.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

One point is to have less places where we actually need tty pointer.
The other is that low_latency is bound to buffer processing and
buffers are now in tty_port. So it makes sense to move low_latency to
tty_port too.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Now, we start converting tty buffer functions to actually use
tty_port. This will allow us to get rid of the need of tty in many
call sites. Only tty_port will needed and hence no more
tty_port_tty_get in those paths.

tty_insert_flip_string this time.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

After commit "TTY: move tty buffers to tty_port", the tty buffers are
not freed in some drivers. This is because tty_port_destructor is not
called whenever a tty_port is freed. This was an assumption I counted
with but was unfortunately untrue. So fix the drivers to fulfil this
assumption.

To be sure, the TTY buffers (and later some stuff) are gone along with
the tty_port, we have to call tty_port_destroy at tear-down places.
This is mostly where the structure containing a tty_port is freed.
This patch does exactly that -- put tty_port_destroy at those places.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Currently we have no way to assign tty->port while performing tty
installation. There are two ways to provide the link tty_struct =>
tty_port. Either by calling tty_port_install from tty->ops->install or
tty_port_register_device called instead of tty_register_device when
the device is being set up after connected.

In this patch we modify most of the drivers to do the latter. When the
drivers use tty_register_device and we have tty_port already, we
switch to tty_port_register_device. So we have the tty_struct =>
tty_port link for free for those.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Acked-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

It does not make the driver less racy though. Close and hangup should
be rewritten and tty refcounting used properly.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Jiri Kosina <jkosina@suse.cz>
Acked-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

And use count from that.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Jiri Kosina <jkosina@suse.cz>
Acked-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

There are two functions which only print a status. Let us do that
directly at places where they are called.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Jiri Kosina <jkosina@suse.cz>
Acked-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Do not touch internal workqueue. Call tty_vhangup instead.

Note that finished hangup does not necessarily mean that all processes
are dead. Especially when the tty is a console. The code assumes that
right now.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Jiri Kosina <jkosina@suse.cz>
Acked-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

* do not test if tty->index is in bounds. It is always.
* tty->index is not a minor! Fix that.

>From now on, let's assume that the parameter of the function is tty
index with base being zero. This makes also the code more readable.

Factually, there is no real change as tty_driver->minor_start is zero,
so the tests are equivalent. But it did not make sense. And if this
had changed eventually, it would have caused troubles.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Acked-by: NJiri Kosina <jkosina@suse.cz>
Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

All num, magic and owner are set by alloc_tty_driver. No need to
re-set them on each allocation site.

pti driver sets something different to what it passes to
alloc_tty_driver. It is not a bug, since we don't use the lines
parameter in any way. Anyway this is fixed, and now we do the right
thing.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Acked-by: NTilman Schmidt <tilman@imap.cc>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Since all that include/linux/if_ppp.h does is #include <linux/ppp-ioctl.h>,
this replaces the occurrences of #include <linux/if_ppp.h> with
#include <linux/ppp-ioctl.h>.

It also corrects an error in Documentation/networking/l2tp.txt, where
it referenced include/linux/if_ppp.h as the source of some definitions
that are actually now defined in include/linux/if_pppol2tp.h.
Signed-off-by: NPaul Mackerras <paulus@samba.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

As planned by Arnd Bergmann, this moves the ipwireless driver to the
drivers/tty/ directory as that's where it really belongs.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Only oddities here are a couple of drivers that bogusly called the ldisc
helpers instead of returning -ENOIOCTLCMD. Fix the bug and the rest goes
away.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Doing tiocmget was such fun we should do tiocmset as well for the same
reasons
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

We don't actually need this and it causes problems for internal use of
this functionality. Currently there is a single use of the FILE * pointer.
That is the serial core which uses it to check tty_hung_up_p. However if
that is true then IO_ERROR is also already set so the check may be removed.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

flush_scheduled_work() is deprecated and scheduled to be removed.
Directly flush the used works instead.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NJiri Kosina <jkosina@suse.cz>
Acked-by: NDavid Sterba <dsterba@suse.cz>

As a fourth step, remove any remaining usages of
dev_node_t from drivers:

- ipwireless can be simplified a bit, as we do not need
  to pass around the (write-only) dev_node_t around.

- avma1_cs can be simplified as well, if we only keep the
  minor number around as "priv" data, not a full-fledged
  struct.
Acked-by: NJiri Kosina <jkosina@suse.cz>
Acked-by: NKarsten Keil  <isdn@linux-pingi.de>
Signed-off-by: NDominik Brodowski <linux@dominikbrodowski.net>

Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This function does not have an error return and returning an error is
instead interpreted as having a lot of pending bytes.

Reported by Jeff Harris who provided a list of some of the remaining
offenders.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This came in via another tree and unfortunately is rather broken on
the tty side. Comment the apparent locking problems for someone who knows
the driver to look at.

Fix the termios and other ioctl handling. The driver was calling the wrong
methods for what it wanted to do but the right ones existed so its a simple
fix up.
Signed-off-by: NAlan Cox <alan@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The drivers below do not use LINUX_VERSION_CODE nor KERNEL_VERSION.
  drivers/char/pcmcia/ipwireless/tty.c
  drivers/char/synclink_gt.c
  drivers/char/xilinx_hwicap/xilinx_hwicap.c

This patch removes the said #include <version.h>.
Signed-off-by: NHuang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

ipwireless: Constify buffer variables
Signed-off-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The device is manufactured by IPWireless.  In some countries (for
example Czech Republic, T-Mobile ISP) this card is shipped for service
called UMTS 4G.

It's a piece of PCMCIA "4G" UMTS PPP networking hardware that presents
itself as a serial character device (i.e.  looks like usual modem to
userspace, accepts AT commands, etc).
Rewieved-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NBen Martel <benm@symmetric.co.nz>
Signed-off-by: NStephen Blackheath <stephen@symmetric.co.nz>
Signed-off-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>