In DMA support, The received data is not pushed to tty until the DMA buffer
is filled. But some megabyte rate chips such as BT expect fast response and
data should be pushed immediately. In order to fix this issue, We suggest
the use of the timer for polling DMA buffer.
In our test, no data loss occurred at high-baudrate as compared with interrupt-
driven (We tested with 3Mbps).
We changes:

- We add timer for polling. If we set poll_timer to 10, every 10ms,
 timer handler checks the residue in the dma buffer and transfer data
 to the tty. Also, last_residue is updated for the next polling.

- poll_timeout is used to prevent the timer's system cost.
  If poll_timeout is set to 3000 and no data is received in 3 seconds,
  we inactivate poll timer and driver falls back to interrupt-driven.
  When data is received again in FIFO and UART irq is occurred, we switch
  back to DMA mode and start polling.

- We use consistent DMA mappings to avoid from the frequent cache operation
  of the timer function for default.

- pl011_dma_rx_chars is modified. the pending size is recalculated because
  data can be taken by polling.

- the polling time is adjusted if dma rx poll is enabled but no rate is
  specified. Ideal polling interval to push 1 character at every interval
  is the reciprocal of 'baud rate / 10 line bits per character / 1000 ms
  per sec'. But It is very aggressive to system. Experimentally,
 '10000000 / baud' is suitable to receive dozens of characters. the poll rate
 can be specified statically by dma_rx_poll_rate of the platform data as well.

Changes compared to v1:
 - Use of consistent DMA mappings.
 - Added dma_rx_poll_rate in platform data to specify the polling interval.
 - Added dma_rx_poll_timeout in platform data to specify the polling timeout.

Changes compared to v2:
 - Use of consistent DMA mappings for default.
 - Added dma_rx_poll_enable in platform data to adjust the polling time
   according to the baud rate.
 - remove unnecessary lock from the polling function.

Signed-off-by: Chanho Min <chanho.min@lge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This commit implements support for using the clk api; this lets us use
the "clocks" property with device tree, instead of having to use
clock-frequency.

Signed-off-by: Emilio López <emilio@elopez.com.ar>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The no_console_suspend option allows the console to write to the UART
during early resume, before the serial port itself is resumed. Such
writes hang indefinitely waiting for TX ready.

This adds a check to the console putchar function to drop characters
instead of hanging if the port hasn't been initialized. That way, we
can use no_console_suspend without risk of hanging.

Signed-off-by: Michael Spang <spang@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This closes a window where the system may hang in resume as soon as the
UART interrupt is enabled and before the mask is restored. The hang occurs
because the driver can't handle IRQs it thinks are masked.

Signed-off-by: Michael Spang <spang@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Since the interrupt mask register is not preserved across system suspend
and it defaults to all interrupts enabled, it is not enough to disable
UART interrupt.

This patch adds free_irq to port shutdown and mask setting to port
startup to handle IRQ disabling in a suspend-friendly way. In addition,
a bug caused by multiple request_irq calls in port startup callback is
fixed.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Consider a situation where I have an ARM based system
and therefore no legacy ports. Say, I have two
memory-mapped ports. I use device tree to describe the
ports. What would be the config options I set so that
I get only the two ports in my system? I do not want
legacy ports being created automatically and I want
it to be flexible enough that it creates the devices
based only on the device tree. I expected setting
SERIAL_8250_RUNTIME_UARTS = 0 to work because the
description said, "Set this to the maximum number of
serial ports you want the kernel to register at boot
time." Unfortunately, even though SERIAL_8250_NR_UARTS
was set to the default value of 4, I did not get any device
nodes (because SERIAL_8250_RUNTIME_UARTS was 0). This
is what this change is addressing.

SERIAL_8250_NR_UARTS controls the maximum number of ports
you can support. SERIAL_8250_RUNTIME_UARTS specifies the
number of ports you want to create automatically for legacy
ports at boot time. All other ports will be created
when serial8250_register_port is called (and if does not exceed
the total number of supported ports as specified by
SERIAL_8250_NR_UARTS).

Signed-off-by: Karthik Manamcheri <karthik.manamcheri@ni.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Support for the WindRiver SBC8560 board was removed in v3.6. But there
are still a few lines depending on its obsolete Kconfig macro. Remove
these now.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Automatic Flow Control capability is not tied to this
property. This is only one way of detecting it. The property
is limited to be used only with 8250 driver.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Peter Hurley <peter@hurleysoftware.com>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

After commit 6865ff22

 ("TTY: do not warn about setting
speed via SPD_*"), we are seeing a build error when DEBUG_FS is
enabled:
drivers/net/caif/caif_serial.c: In function 'update_tty_status':
drivers/net/caif/caif_serial.c:94:11: error: 'struct tty_struct' has no member named 'warned'

Fix the error by removing the reference to the variable as it was
not set in the last decade (as documented in the changelog of the
commit above).

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Sjur Braendeland <sjur.brandeland@stericsson.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The datesheet clearly states, that writing low bits to the
XUARTPS_IDR register have no effect. Remove the write.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Support for SH7367 and SH7377 got removed in v3.8. Now remove their
last Kconfig macros.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This will reduce the need for extra types in 8250.c just
in case the fifo size differs from the standard.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

In most cases the tx_loadsz is the same as fifosize. This
will store the fifosize in it if it was not separately
delivered from the driver.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This reverts commit 27b351c5

.  It caused
problems with the build.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Bill Pemberton <wfp5p@viridian.itc.virginia.edu>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

remove cast for kmalloc return value.

Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

remove cast for kzalloc return value.

Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The following commits:
* 6732c8bb (TTY: switch
  tty_schedule_flip)
* 2e124b4a (TTY: switch
  tty_flip_buffer_push)
* 05c7cd39 (TTY: switch
  tty_insert_flip_string)
* 92a19f9c (TTY: switch
  tty_insert_flip_char)
* 227434f8

 (TTY: switch
  tty_buffer_request_room to tty_port)

introduced a potential NULL dereference to some drivers. In
particular, when the device is used as a console, incoming bytes can
kill the box. This is caused by removed checks for TTY against NULL.

It happened because it was unclear to me why the checks were there. I
assumed them superfluous because the interrupts were unbound or
otherwise stopped. But this is not the case for consoles for these
drivers, as was pointed out by David Miller.

Now, this patch re-introduces the checks (at this point we check
port->state, not the tty proper, as we do not care about tty pointers
anymore). For both of the drivers, we place the check below the
handling of break signal so that sysrq can actually work. (One needs
to issue a break and then sysrq key within the following 5 seconds.)

We do not change sc26xx, sunhv, and sunsu here because they behave the
same as before.  People having that hardware should fix the driver
eventually, however. They always could unconditionally dereference tty
in receive_chars, port->state in uart_handle_dcd_change, and
up->port.state->port.tty.

There is perhaps more to fix in all those drivers, but they are at
least in a state they were before.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: sparclinux@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tty_perform_flush() can deadlock when called while holding
a line discipline reference. By definition, all ldisc drivers
hold a ldisc reference, so calls originating from ldisc drivers
must not block for a ldisc reference.

The deadlock can occur when:
  CPU 0                    |  CPU 1
                           |
tty_ldisc_ref(tty)         |
....                       | <line discipline halted>
tty_ldisc_ref_wait(tty)    |
                           |

CPU 0 cannot progess because it cannot obtain an ldisc reference
with the line discipline has been halted (thus no new references
are granted).
CPU 1 cannot progress because an outstanding ldisc reference
has not been released.

An in-tree call-tree audit of tty_perform_flush() [1] shows 5
ldisc drivers calling tty_perform_flush() indirectly via
n_tty_ioctl_helper() and 2 ldisc drivers calling directly.
A single tty driver safely uses the function.

[1]
Recursive usage:

/* These functions are line discipline ioctls and thus
 * recursive wrt line discipline references */

tty_perform_flush() - ./drivers/tty/tty_ioctl.c
    n_tty_ioctl_helper()
        hci_uart_tty_ioctl(default) - drivers/bluetooth/hci_ldisc.c (N_HCI)
        n_hdlc_tty_ioctl(default) - drivers/tty/n_hdlc.c (N_HDLC)
        gsmld_ioctl(default) - drivers/tty/n_gsm.c (N_GSM0710)
        n_tty_ioctl(default) - drivers/tty/n_tty.c (N_TTY)
        gigaset_tty_ioctl(default) - drivers/isdn/gigaset/ser-gigaset.c (N_GIGASET_M101)
    ppp_synctty_ioctl(TCFLSH) - drivers/net/ppp/pps_synctty.c
    ppp_asynctty_ioctl(TCFLSH) - drivers/net/ppp/ppp_async.c

Non-recursive use:

tty_perform_flush() - drivers/tty/tty_ioctl.c
    ipw_ioctl(TCFLSH) - drivers/tty/ipwireless/tty.c
       /* This function is a tty i/o ioctl method, which
        * is invoked by tty_ioctl() */

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tty_ioctl() already waits until sent.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Now that tty_ldisc_assign() is a one-line file-scoped function,
remove it and perform the simple assignment at its call sites.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Merge get_ldisc() into its only call site.
Note how, after merging, the unsafe acquire of an ldisc reference
is obvious.

   CPU 0 in tty_ldisc_try()         |  CPU 1 in tty_ldisc_halt()
                                    |
test_bit(TTY_LDISC, &tty_flags)     |
if (true)                           |  clear_bit(TTY_LDISC, &tty_flags)
  tty->ldisc != 0?                  |  atomic_read(&tty->ldisc->users)
  if (true)                         |  ret_val == 1?
    atomic_inc(&tty->ldisc->users)  |  if (false)
                                    |    wait
                                    |
<goes on assuming safe ldisc use>   |  <doesn't wait - proceeds w/ close>
                                    |

The spin lock in tty_ldisc_try() does nothing wrt synchronizing
the ldisc halt since it's not acquired as part of halting.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tty_ldisc_ref()/tty_ldisc_unref() have usage semantics
equivalent to down_read_trylock()/up_read(). Only
callers of tty_ldisc_put() are performing the additional
operations necessary for proper ldisc teardown, and then only
after ensuring no outstanding 'read lock' remains.

Thus, tty_ldisc_unref() should never be the last reference;
WARN if it is. Conversely, tty_ldisc_put() should never be
destructing if the use count != 1.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

test_bit() is already atomic; drop mutex lock/unlock.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Expected typical debug log:
[  582.721965] tty_open: opening pts3...
[  582.721970] tty_open: opening pts3...
[  582.721977] tty_release: pts3 (tty count=3)...
[  582.721980] tty_release: ptm3 (tty count=1)...
[  582.722015] pts3 vhangup...
[  582.722020] tty_ldisc_hangup: pts3: closing ldisc: ffff88007a920540
[  582.724128] tty_release: pts3 (tty count=2)...
[  582.724217] tty_ldisc_hangup: pts3: re-opened ldisc: ffff88007a920580
[  582.724221] tty_release: ptm3: final close
[  582.724234] tty_ldisc_release: ptm3: closing ldisc: ffff88007a920a80
[  582.724238] tty_ldisc_release: ptm3: ldisc closed
[  582.724241] tty_release: ptm3: freeing structure...
[  582.724741] tty_open: opening pts3...

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Expected typical log output:
[    2.437211] tty_open: opening pts1...
[    2.443376] tty_open: opening pts5...
[    2.447830] tty_release: ptm0 (tty count=1)...
[    2.447849] pts0 vhangup...
[    2.447865] tty_release: ptm0: final close
[    2.447876] tty_release: ptm0: freeing structure...
[    2.451634] tty_release: tty1 (tty count=1)...
[    2.451638] tty_release: tty1: final close
[    2.451654] tty_release: tty1: freeing structure...
[    2.452505] tty_release: pts5 (tty count=2)...
[    2.453029] tty_open: opening pts0...

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This comment is a victim of code migration from
"tty: Fix the ldisc hangup race"; re-parent it.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The tty core relies on the ldisc layer for synchronizing destruction
of the tty. Instead, the final tty release must wait for any pending tty
work to complete prior to tty destruction.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Waiting for buffer work to complete is not required for safely
performing changes to the line discipline, once the line discipline
is halted. The buffer work routine, flush_to_ldisc(), will be
unable to acquire an ldisc ref and all existing references were
waited until released (so it can't already have one).

Ensure running buffer work which may reference the soon-to-be-gone
tty completes and any buffer work running after this point retrieves
a NULL tty.

Also, ensure all buffer work is cancelled on port destruction.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tty_ldisc_hangup() guarantees the ldisc is enabled (or that there
is no ldisc). Since __tty_hangup() was the only user, re-define
tty_ldisc_enable() in file-scope.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Buffer work may already be pending when the n_tty ldisc is re-opened,
eg., when setting the ldisc (via TIOCSETD ioctl) and when hanging up
the tty. Since n_tty_set_room() may restart buffer work, first ensure
the ldisc is completely initialized.

Factor n_tty_set_room() out of reset_buffer_flags() (only 2 callers)
and reorganize n_tty_open() to set termios last; buffer work will
be restarted there if necessary, after the char_map is properly
initialized.

Fixes this WARNING:

[  549.561769] ------------[ cut here ]------------
[  549.598755] WARNING: at drivers/tty/n_tty.c:160 n_tty_set_room+0xff/0x130()
[  549.604058] scheduling buffer work for halted ldisc
[  549.607741] Pid: 9417, comm: trinity-child28 Tainted: G      D W 3.7.0-next-20121217-sasha-00023-g8689ef9 #219
[  549.652580] Call Trace:
[  549.662754]  [<ffffffff81c432cf>] ? n_tty_set_room+0xff/0x130
[  549.665458]  [<ffffffff8110cae7>] warn_slowpath_common+0x87/0xb0
[  549.668257]  [<ffffffff8110cb71>] warn_slowpath_fmt+0x41/0x50
[  549.671007]  [<ffffffff81c432cf>] n_tty_set_room+0xff/0x130
[  549.673268]  [<ffffffff81c44597>] reset_buffer_flags+0x137/0x150
[  549.675607]  [<ffffffff81c45b71>] n_tty_open+0x131/0x1c0
[  549.677699]  [<ffffffff81c47824>] tty_ldisc_open.isra.5+0x54/0x70
[  549.680147]  [<ffffffff81c482bf>] tty_ldisc_hangup+0x11f/0x1e0
[  549.682409]  [<ffffffff81c3fa17>] __tty_hangup+0x137/0x440
[  549.684634]  [<ffffffff81c3fd49>] tty_vhangup+0x9/0x10
[  549.686443]  [<ffffffff81c4a42c>] pty_close+0x14c/0x160
[  549.688446]  [<ffffffff81c41225>] tty_release+0xd5/0x490
[  549.690460]  [<ffffffff8127d8a2>] __fput+0x122/0x250
[  549.692577]  [<ffffffff8127d9d9>] ____fput+0x9/0x10
[  549.694534]  [<ffffffff811348c2>] task_work_run+0xb2/0xf0
[  549.696349]  [<ffffffff81113c6d>] do_exit+0x36d/0x580
[  549.698286]  [<ffffffff8107d964>] ? syscall_trace_enter+0x24/0x2e0
[  549.702729]  [<ffffffff81113f4a>] do_group_exit+0x8a/0xc0
[  549.706775]  [<ffffffff81113f92>] sys_exit_group+0x12/0x20
[  549.711088]  [<ffffffff83cfab18>] tracesys+0xe1/0xe6
[  549.728001] ---[ end trace 73eb41728f11f87e ]---

Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The driver is no longer unthrottled on buffer reset, so remove
comments that claim it is.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

SAK work may schedule hangup work (if TTY_SOFT_SAK is defined), thus
SAK work must be flushed before hangup work.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The pty driver does not obtain an ldisc reference to the linked
tty when writing. When the ldiscs are sequentially halted, it
is possible for one ldisc to be halted, and before the second
ldisc can be halted, a concurrent write schedules buffer work on
the first ldisc. This can lead to an access-after-free error when
the scheduled buffer work starts on the closed ldisc.

Prevent subsequent use after halt by performing each stage
of the halt on both ttys.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

In preparation for destructing and freeing the tty, the line discipline
must first be brought to an inactive state before it can be destructed.
This line discipline shutdown must:
 - disallow new users of the ldisc
 - wait for existing ldisc users to finish
 - only then, cancel/flush their pending/running work

Factor tty_ldisc_wait_idle() from tty_set_ldisc() and tty_ldisc_kill()
to ensure this shutdown order.

Failure to provide this guarantee can result in scheduled work
running after the tty has already been freed, as indicated in the
following log message:

[   88.331234] WARNING: at drivers/tty/tty_buffer.c:435 flush_to_ldisc+0x194/0x1d0()
[   88.334505] Hardware name: Bochs
[   88.335618] tty is bad=-1
[   88.335703] Modules linked in: netconsole configfs bnep rfcomm bluetooth ......
[   88.345272] Pid: 39, comm: kworker/1:1 Tainted: G        W    3.7.0-next-20121129+ttydebug-xeon #20121129+ttydebug
[   88.347736] Call Trace:
[   88.349024]  [<ffffffff81058aff>] warn_slowpath_common+0x7f/0xc0
[   88.350383]  [<ffffffff81058bf6>] warn_slowpath_fmt+0x46/0x50
[   88.351745]  [<ffffffff81432bd4>] flush_to_ldisc+0x194/0x1d0
[   88.353047]  [<ffffffff816f7fe1>] ? _raw_spin_unlock_irq+0x21/0x50
[   88.354190]  [<ffffffff8108a809>] ? finish_task_switch+0x49/0xe0
[   88.355436]  [<ffffffff81077ad1>] process_one_work+0x121/0x490
[   88.357674]  [<ffffffff81432a40>] ? __tty_buffer_flush+0x90/0x90
[   88.358954]  [<ffffffff81078c84>] worker_thread+0x164/0x3e0
[   88.360247]  [<ffffffff81078b20>] ? manage_workers+0x120/0x120
[   88.361282]  [<ffffffff8107e230>] kthread+0xc0/0xd0
[   88.362284]  [<ffffffff816f0000>] ? cmos_do_probe+0x2eb/0x3bf
[   88.363391]  [<ffffffff8107e170>] ? flush_kthread_worker+0xb0/0xb0
[   88.364797]  [<ffffffff816fff6c>] ret_from_fork+0x7c/0xb0
[   88.366087]  [<ffffffff8107e170>] ? flush_kthread_worker+0xb0/0xb0
[   88.367266] ---[ end trace 453a7c9f38fbfec0 ]---

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tty_ldisc_halt() will use the file-scoped function, tty_ldisc_wait_idle(),
in the following patch.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Flip buffer work cannot be cancelled until all outstanding ldisc
references have been released. Convert the ldisc ref wait into
a full ldisc halt with buffer work cancellation.

Note that the legacy mutex is not held while cancelling.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Since the tty->ldisc is prevented from being changed by tty_set_ldisc()
when a tty is being hung up, re-testing the ldisc user count is
unnecessary -- ie, it cannot be a different ldisc and the user count
cannot have increased (assuming the caller meets the precondition that
TTY_LDISC flag is cleared)

Removal of the 'early-out' locking optimization is necessary for
the subsequent patch 'tty: Fix ldisc halt sequence on hangup'.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>