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Documentation: improve line discipline method descriptions 

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 <tilman@imap.cc>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tilman Schmidt 2015-09-30 01:45:11 +02:00 committed by Greg Kroah-Hartman
parent 850b37a71b
commit 1a76eb5b04
1 changed files with 39 additions and 21 deletions
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60
Documentation/serial/tty.txt
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@ -39,8 +39,13 @@ TTY side interfaces:
open() - Called when the line discipline is attached to
the terminal. No other call into the line
discipline for this tty will occur until it
completes successfully. Returning an error will
prevent the ldisc from being attached. Can sleep.
completes successfully. Should initialize any
state needed by the ldisc, and set receive_room
in the tty_struct to the maximum amount of data
the line discipline is willing to accept from the
driver with a single call to receive_buf().
Returning an error will prevent the ldisc from
being attached. Can sleep.
close() - This is called on a terminal when the line
discipline is being unplugged. At the point of
@ -52,9 +57,16 @@ hangup() - Called when the tty line is hung up.
No further calls into the ldisc code will occur.
The return value is ignored. Can sleep.
write() - A process is writing data through the line
discipline. Multiple write calls are serialized
by the tty layer for the ldisc. May sleep.
read() - (optional) A process requests reading data from
the line. Multiple read calls may occur in parallel
and the ldisc must deal with serialization issues.
If not defined, the process will receive an EIO
error. May sleep.
write() - (optional) A process requests writing data to the
line. Multiple write calls are serialized by the
tty layer for the ldisc. If not defined, the
process will receive an EIO error. May sleep.
flush_buffer() - (optional) May be called at any point between
open and close, and instructs the line discipline
@ -69,27 +81,33 @@ set_termios() - (optional) Called on termios structure changes.
termios semaphore so allowed to sleep. Serialized
against itself only.
read() - Move data from the line discipline to the user.
Multiple read calls may occur in parallel and the
ldisc must deal with serialization issues. May
sleep.
poll() - (optional) Check the status for the poll/select
calls. Multiple poll calls may occur in parallel.
May sleep.
poll() - Check the status for the poll/select calls. Multiple
poll calls may occur in parallel. May sleep.
ioctl() - (optional) Called when an ioctl is handed to the
tty layer that might be for the ldisc. Multiple
ioctl calls may occur in parallel. May sleep.
ioctl() - Called when an ioctl is handed to the tty layer
that might be for the ldisc. Multiple ioctl calls
may occur in parallel. May sleep.
compat_ioctl() - Called when a 32 bit ioctl is handed to the tty layer
that might be for the ldisc. Multiple ioctl calls
may occur in parallel. May sleep.
compat_ioctl() - (optional) Called when a 32 bit ioctl is handed
to the tty layer that might be for the ldisc.
Multiple ioctl calls may occur in parallel.
May sleep.
Driver Side Interfaces:
receive_buf() - Hand buffers of bytes from the driver to the ldisc
for processing. Semantics currently rather
mysterious 8(
receive_buf() - (optional) Called by the low-level driver to hand
a buffer of received bytes to the ldisc for
processing. The number of bytes is guaranteed not
to exceed the current value of tty->receive_room.
All bytes must be processed.
receive_buf2() - (optional) Called by the low-level driver to hand
a buffer of received bytes to the ldisc for
processing. Returns the number of bytes processed.
If both receive_buf() and receive_buf2() are
defined, receive_buf2() should be preferred.
write_wakeup() - May be called at any point between open and close.
The TTY_DO_WRITE_WAKEUP flag indicates if a call