1==================== 2Low Level Serial API 3==================== 4 5 6This document is meant as a brief overview of some aspects of the new serial 7driver. It is not complete, any questions you have should be directed to 8<rmk@arm.linux.org.uk> 9 10The reference implementation is contained within amba-pl011.c. 11 12 13 14Low Level Serial Hardware Driver 15-------------------------------- 16 17The low level serial hardware driver is responsible for supplying port 18information (defined by uart_port) and a set of control methods (defined 19by uart_ops) to the core serial driver. The low level driver is also 20responsible for handling interrupts for the port, and providing any 21console support. 22 23 24Console Support 25--------------- 26 27The serial core provides a few helper functions. This includes identifying 28the correct port structure (via uart_get_console()) and decoding command line 29arguments (uart_parse_options()). 30 31There is also a helper function (uart_console_write()) which performs a 32character by character write, translating newlines to CRLF sequences. 33Driver writers are recommended to use this function rather than implementing 34their own version. 35 36 37Locking 38------- 39 40It is the responsibility of the low level hardware driver to perform the 41necessary locking using port->lock. There are some exceptions (which 42are described in the struct uart_ops listing below.) 43 44There are two locks. A per-port spinlock, and an overall semaphore. 45 46From the core driver perspective, the port->lock locks the following 47data:: 48 49 port->mctrl 50 port->icount 51 port->state->xmit.head (circ_buf->head) 52 port->state->xmit.tail (circ_buf->tail) 53 54The low level driver is free to use this lock to provide any additional 55locking. 56 57The port_sem semaphore is used to protect against ports being added/ 58removed or reconfigured at inappropriate times. Since v2.6.27, this 59semaphore has been the 'mutex' member of the tty_port struct, and 60commonly referred to as the port mutex. 61 62 63uart_ops 64-------- 65 66.. kernel-doc:: include/linux/serial_core.h 67 :identifiers: uart_ops 68 69Other functions 70--------------- 71 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 uart_console_write 77 uart_parse_earlycon uart_parse_options uart_set_options 78 uart_get_lsr_info uart_handle_dcd_change uart_handle_cts_change 79 uart_try_toggle_sysrq uart_get_console 80 81.. kernel-doc:: include/linux/serial_core.h 82 :identifiers: uart_port_tx_limited uart_port_tx 83 84Other notes 85----------- 86 87It is intended some day to drop the 'unused' entries from uart_port, and 88allow low level drivers to register their own individual uart_port's with 89the core. This will allow drivers to use uart_port as a pointer to a 90structure containing both the uart_port entry with their own extensions, 91thus:: 92 93 struct my_port { 94 struct uart_port port; 95 int my_stuff; 96 }; 97 98Modem control lines via GPIO 99---------------------------- 100 101Some helpers are provided in order to set/get modem control lines via GPIO. 102 103.. kernel-doc:: drivers/tty/serial/serial_mctrl_gpio.c 104 :identifiers: mctrl_gpio_init mctrl_gpio_free mctrl_gpio_to_gpiod 105 mctrl_gpio_set mctrl_gpio_get mctrl_gpio_enable_ms 106 mctrl_gpio_disable_ms 107