1 .. SPDX-License-Identifier: GPL-2.0 2 3 === 4 TTY 5 === 6 7 Teletypewriter (TTY) layer takes care of all those serial devices. Including 8 the virtual ones like pseudoterminal (PTY). 9 10 TTY structures 11 ============== 12 13 There are several major TTY structures. Every TTY device in a system has a 14 corresponding struct tty_port. These devices are maintained by a TTY driver 15 which is struct tty_driver. This structure describes the driver but also 16 contains a reference to operations which could be performed on the TTYs. It is 17 struct tty_operations. Then, upon open, a struct tty_struct is allocated and 18 lives until the final close. During this time, several callbacks from struct 19 tty_operations are invoked by the TTY layer. 20 21 Every character received by the kernel (both from devices and users) is passed 22 through a preselected :doc:`tty_ldisc` (in 23 short ldisc; in C, struct tty_ldisc_ops). Its task is to transform characters 24 as defined by a particular ldisc or by user too. The default one is n_tty, 25 implementing echoes, signal handling, jobs control, special characters 26 processing, and more. The transformed characters are passed further to 27 user/device, depending on the source. 28 29 In-detail description of the named TTY structures is in separate documents: 30 31 .. toctree:: 32 :maxdepth: 2 33 34 tty_driver 35 tty_port 36 tty_struct 37 tty_ldisc 38 tty_buffer 39 tty_ioctl 40 tty_internals 41 console 42 43 Writing TTY Driver 44 ================== 45 46 Before one starts writing a TTY driver, they must consider 47 :doc:`Serial <../serial/driver>` and :doc:`USB Serial <../../usb/usb-serial>` 48 layers first. Drivers for serial devices can often use one of these specific 49 layers to implement a serial driver. Only special devices should be handled 50 directly by the TTY Layer. If you are about to write such a driver, read on. 51 52 A *typical* sequence a TTY driver performs is as follows: 53 54 #. Allocate and register a TTY driver (module init) 55 #. Create and register TTY devices as they are probed (probe function) 56 #. Handle TTY operations and events like interrupts (TTY core invokes the 57 former, the device the latter) 58 #. Remove devices as they are going away (remove function) 59 #. Unregister and free the TTY driver (module exit) 60 61 Steps regarding driver, i.e. 1., 3., and 5. are described in detail in 62 :doc:`tty_driver`. For the other two (devices handling), look into 63 :doc:`tty_port`. 64 65 Other Documentation 66 =================== 67 68 Miscellaneous documentation can be further found in these documents: 69 70 .. toctree:: 71 :maxdepth: 2 72 73 moxa-smartio 74 n_gsm 75 n_tty
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