linux-toradex.git/Documentation/serial, branch v4.6-rc6

tty: Remove chars_in_buffer() line discipline method

2016-01-27T23:01:44+00:00

The chars_in_buffer() line discipline method serves no functional
purpose, other than as a (dubious) debugging aid for mostly bit-rotting
drivers. Despite being documented as an optional method, every caller
is unconditionally executed (although conditionally compiled).
Furthermore, direct tty->ldisc access without an ldisc ref is unsafe.
Lastly, N_TTY's chars_in_buffer() has warned of removal since 3.12.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

Documentation: improve line discipline method descriptions

2015-10-05T03:53:26+00:00

Mention that the ldisc open method must set tty->receive_room, and
that many methods are optional. Add description of receive_buf2 method.

Signed-off-by: Tilman Schmidt 
Reviewed-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

serial: mctrl_gpio: implement interrupt handling

2015-10-04T17:47:51+00:00

This allows to reduce the per-driver boiler plate considerably.

Signed-off-by: Uwe Kleine-König 
Reviewed-by: Nicolas Ferre 
Signed-off-by: Greg Kroah-Hartman

Doc: serial-rs485.txt: update RS485 driver interface

2015-06-13T00:39:51+00:00

Since commit a5f276f10ff7 (serial_core: Handle TIOC[GS]RS485 ioctls.,
2014-11-06) serial_core handles RS485 ioctls. Drivers only need to implement
the rs485_config callback. Update serial-rs485.txt to reflect these changes.

Signed-off-by: Baruch Siach 
Signed-off-by: Greg Kroah-Hartman

Doc: tty.txt: remove mention of the BKL

2015-06-13T00:39:51+00:00

The BKL is long gone, no need to kill the dead.

Signed-off-by: Baruch Siach 
Signed-off-by: Greg Kroah-Hartman

pty: Fix input race when closing

2015-05-10T17:26:37+00:00

A read() from a pty master may mistakenly indicate EOF (errno == -EIO)
after the pty slave has closed, even though input data remains to be read.
For example,

       pty slave       |        input worker        |    pty master
                       |                            |
                       |                            |   n_tty_read()
pty_write()            |                            |     input avail? no
  add data             |                            |     sleep
  schedule worker  --->|                            |     .
                       |---> flush_to_ldisc()       |     .
pty_close()            |       fill read buffer     |     .
  wait for worker      |       wakeup reader    --->|     .
                       |       read buffer full?    |---> input avail ? yes
                       |<---   yes - exit worker    |     copy 4096 bytes to user
  TTY_OTHER_CLOSED <---|                            |<--- kick worker
                       |                            |

		                **** New read() before worker starts ****

                       |                            |   n_tty_read()
                       |                            |     input avail? no
                       |                            |     TTY_OTHER_CLOSED? yes
                       |                            |     return -EIO

Several conditions are required to trigger this race:
1. the ldisc read buffer must become full so the input worker exits
2. the read() count parameter must be >= 4096 so the ldisc read buffer
   is empty
3. the subsequent read() occurs before the kicked worker has processed
   more input

However, the underlying cause of the race is that data is pipelined, while
tty state is not; ie., data already written by the pty slave end is not
yet visible to the pty master end, but state changes by the pty slave end
are visible to the pty master end immediately.

Pipeline the TTY_OTHER_CLOSED state through input worker to the reader.
1. Introduce TTY_OTHER_DONE which is set by the input worker when
   TTY_OTHER_CLOSED is set and either the input buffers are flushed or
   input processing has completed. Readers/polls are woken when
   TTY_OTHER_DONE is set.
2. Reader/poll checks TTY_OTHER_DONE instead of TTY_OTHER_CLOSED.
3. A new input worker is started from pty_close() after setting
   TTY_OTHER_CLOSED, which ensures the TTY_OTHER_DONE state will be
   set if the last input worker is already finished (or just about to
   exit).

Remove tty_flush_to_ldisc(); no in-tree callers.

Fixes: 52bce7f8d4fc ("pty, n_tty: Simplify input processing on final close")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=96311
BugLink: http://bugs.launchpad.net/bugs/1429756
Cc:  # 3.19+
Reported-by: Andy Whitcroft 
Reported-by: H.J. Lu 
Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

serial: Fix locking for uart driver set_termios() method

2014-11-06T02:53:54+00:00

The low-level uart driver may modify termios settings to override
settings that are not compatible with the uart, such as CRTSCTS.
Thus, callers of the low-level uart driver's set_termios() method must
hold termios_rwsem write lock to prevent concurrent access to termios,
in case such override occurs.

The termios_rwsem lock requirement does not extend to console setup
(ie., uart_set_options), as console setup cannot race with tty
operations. Nor does this lock requirement extend to functions which
cannot be concurrent with tty ioctls (ie., uart_port_startup() and
uart_resume_port()).

Further, always claim the port mutex to protect hardware
re-reprogramming in the set_termios() uart driver method. Note this
is unnecessary for console initialization in uart_set_options()
which cannot be concurrent with other uart operations.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

Merge tag 'tty-3.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2014-10-08T10:52:11+00:00

Pull tty/serial driver updates from Greg KH:
 "Here's the big tty/serial driver patchset for 3.18-rc1.

  Lots of little things in here, some good work from Peter Hurley on the
  tty core, and in lots of drivers.  There are also lots of other driver
  updates in here as well, full details in the changelogs.

  All have been in the linux-next tree for a while"

* tag 'tty-3.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (99 commits)
  Revert "serial/core: Initialize the console pm state"
  tty: serial: 8250: use 32bit variable for rpm_tx_active
  tty: serial: msm: Add earlycon support
  serial/core: Initialize the console pm state
  serial: asc: Conditionally use readl_relaxed (COMPILE_TEST)
  serial: of-serial: add PM suspend/resume support
  m68k: AMIGA_BUILTIN_SERIAL should depend on TTY
  asm/uapi: Add definition of TIOC[SG]RS485
  tty/metag_da: Add console_poll module parameter
  serial: 8250_pci: remove rts_n override from Baytrail quirk
  serial: cadence: Add generic earlycon support
  serial: imx: change the wait even to interruptiable
  serial: imx: terminate the RX DMA when the UART is suspending
  serial: imx: fix throttle/unthrottle callbacks for hardware assisted flow control
  serial: 8250: Add Quark X1000 to 8250_pci.c
  tty: omap-serial: pull out calculation from baud_is_mode16
  tty: omap-serial: fix division by zero
  xen_hvc: no reason to write the type key on xenstore
  tty: serial: 8250_core: remove UART_IER_RDI in serial8250_stop_rx()
  tty: serial: 8250_core: use the ->line argument as a hint in serial8250_find_match_or_unused()
  ...

serial: Fix send_xchar() handlers

2014-09-08T23:22:42+00:00

START_CHAR() & STOP_CHAR() can be disabled if set to '\0'
(__DISABLED_CHAR).  UART drivers which define a send_xchar()
handler must not transmit __DISABLED_CHAR.

Document requirement.

Affected drivers:
sunsab
sunhv

cc: David S. Miller 
cc: 
Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

Documentation: serial: fix header path

2014-09-08T23:10:01+00:00

RS485 related structure will be defined in user space API
header.

Signed-off-by: Yegor Yefremov 
Signed-off-by: Greg Kroah-Hartman