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3f19fed8d0
We now have all the kernel-doc comments in the code ready. So add a couple of documents dragging those into generated docs from Documentation/. There is only some sugar text around included kernel-docs here. It's a complete chapter, to be extended later as desired. This is a solid cornerstone for the time being, I believe. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Link: https://lore.kernel.org/r/20211126081611.11001-24-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
63 lines
2.3 KiB
ReStructuredText
63 lines
2.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===
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TTY
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===
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Teletypewriter (TTY) layer takes care of all those serial devices. Including
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the virtual ones like pseudoterminal (PTY).
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TTY structures
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==============
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There are several major TTY structures. Every TTY device in a system has a
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corresponding struct tty_port. These devices are maintained by a TTY driver
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which is struct tty_driver. This structure describes the driver but also
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contains a reference to operations which could be performed on the TTYs. It is
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struct tty_operations. Then, upon open, a struct tty_struct is allocated and
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lives until the final close. During this time, several callbacks from struct
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tty_operations are invoked by the TTY layer.
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Every character received by the kernel (both from devices and users) is passed
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through a preselected :doc:`tty_ldisc` (in
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short ldisc; in C, struct tty_ldisc_ops). Its task is to transform characters
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as defined by a particular ldisc or by user too. The default one is n_tty,
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implementing echoes, signal handling, jobs control, special characters
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processing, and more. The transformed characters are passed further to
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user/device, depending on the source.
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In-detail description of the named TTY structures is in separate documents:
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.. toctree::
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:maxdepth: 2
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tty_driver
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tty_port
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tty_struct
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tty_ldisc
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tty_buffer
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n_tty
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tty_internals
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Writing TTY Driver
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==================
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Before one starts writing a TTY driver, they must consider
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:doc:`Serial <../driver-api/serial/driver>` and :doc:`USB Serial
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<../usb/usb-serial>` layers
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first. Drivers for serial devices can often use one of these specific layers to
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implement a serial driver. Only special devices should be handled directly by
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the TTY Layer. If you are about to write such a driver, read on.
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A *typical* sequence a TTY driver performs is as follows:
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#. Allocate and register a TTY driver (module init)
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#. Create and register TTY devices as they are probed (probe function)
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#. Handle TTY operations and events like interrupts (TTY core invokes the
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former, the device the latter)
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#. Remove devices as they are going away (remove function)
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#. Unregister and free the TTY driver (module exit)
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Steps regarding driver, i.e. 1., 3., and 5. are described in detail in
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:doc:`tty_driver`. For the other two (devices handling), look into
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:doc:`tty_port`.
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