6 This document is meant as a brief overview of some aspects of the new serial
7 driver. It is not complete, any questions you have should be directed to
10 The reference implementation is contained within amba-pl011.c.
14 Low Level Serial Hardware Driver
15 --------------------------------
17 The low level serial hardware driver is responsible for supplying port
18 information (defined by uart_port) and a set of control methods (defined
19 by uart_ops) to the core serial driver. The low level driver is also
20 responsible for handling interrupts for the port, and providing any
27 The serial core provides a few helper functions. This includes identifing
28 the correct port structure (via uart_get_console) and decoding command line
29 arguments (uart_parse_options).
31 There is also a helper function (uart_console_write) which performs a
32 character by character write, translating newlines to CRLF sequences.
33 Driver writers are recommended to use this function rather than implementing
40 It is the responsibility of the low level hardware driver to perform the
41 necessary locking using port->lock. There are some exceptions (which
42 are described in the struct uart_ops listing below.)
44 There are two locks. A per-port spinlock, and an overall semaphore.
46 From the core driver perspective, the port->lock locks the following
51 port->state->xmit.head (circ_buf->head)
52 port->state->xmit.tail (circ_buf->tail)
54 The low level driver is free to use this lock to provide any additional
57 The port_sem semaphore is used to protect against ports being added/
58 removed or reconfigured at inappropriate times. Since v2.6.27, this
59 semaphore has been the 'mutex' member of the tty_port struct, and
60 commonly referred to as the port mutex.
66 .. kernel-doc:: include/linux/serial_core.h
67 :identifiers: uart_ops
72 .. kernel-doc:: drivers/tty/serial/serial_core.c
73 :identifiers: uart_update_timeout uart_get_baud_rate uart_get_divisor
74 uart_match_port uart_write_wakeup uart_register_driver
75 uart_unregister_driver uart_suspend_port uart_resume_port
76 uart_add_one_port uart_remove_one_port
81 It is intended some day to drop the 'unused' entries from uart_port, and
82 allow low level drivers to register their own individual uart_port's with
83 the core. This will allow drivers to use uart_port as a pointer to a
84 structure containing both the uart_port entry with their own extensions,
88 struct uart_port port;
92 Modem control lines via GPIO
93 ----------------------------
95 Some helpers are provided in order to set/get modem control lines via GPIO.
97 .. kernel-doc:: drivers/tty/serial/serial_mctrl_gpio.c
98 :identifiers: mctrl_gpio_init mctrl_gpio_free mctrl_gpio_to_gpiod
99 mctrl_gpio_set mctrl_gpio_get mctrl_gpio_enable_ms
100 mctrl_gpio_disable_ms