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Commit 1a76eb5b authored by Tilman Schmidt's avatar Tilman Schmidt Committed by Greg Kroah-Hartman
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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: default avatarTilman Schmidt <tilman@imap.cc>
Reviewed-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 850b37a7

Documentation/serial/tty.txt

+39 −21
Original line number Diff line number Diff line
@@ -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()		-	Check the status for the poll/select calls. Multiple

			poll calls may occur in parallel. May sleep.

poll()		-	(optional) Check the status for the poll/select

			calls. Multiple poll 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. 

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.



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