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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 | ==================== Low Level Serial API ==================== This document is meant as a brief overview of some aspects of the new serial driver. It is not complete, any questions you have should be directed to <rmk@arm.linux.org.uk> The reference implementation is contained within amba-pl011.c. Low Level Serial Hardware Driver -------------------------------- The low level serial hardware driver is responsible for supplying port information (defined by uart_port) and a set of control methods (defined by uart_ops) to the core serial driver. The low level driver is also responsible for handling interrupts for the port, and providing any console support. Console Support --------------- The serial core provides a few helper functions. This includes identifing the correct port structure (via uart_get_console()) and decoding command line arguments (uart_parse_options()). There is also a helper function (uart_console_write()) which performs a character by character write, translating newlines to CRLF sequences. Driver writers are recommended to use this function rather than implementing their own version. Locking ------- It is the responsibility of the low level hardware driver to perform the necessary locking using port->lock. There are some exceptions (which are described in the struct uart_ops listing below.) There are two locks. A per-port spinlock, and an overall semaphore. From the core driver perspective, the port->lock locks the following data:: port->mctrl port->icount port->state->xmit.head (circ_buf->head) port->state->xmit.tail (circ_buf->tail) The low level driver is free to use this lock to provide any additional locking. The port_sem semaphore is used to protect against ports being added/ removed or reconfigured at inappropriate times. Since v2.6.27, this semaphore has been the 'mutex' member of the tty_port struct, and commonly referred to as the port mutex. uart_ops -------- .. kernel-doc:: include/linux/serial_core.h :identifiers: uart_ops Other functions --------------- .. kernel-doc:: drivers/tty/serial/serial_core.c :identifiers: uart_update_timeout uart_get_baud_rate uart_get_divisor uart_match_port uart_write_wakeup uart_register_driver uart_unregister_driver uart_suspend_port uart_resume_port uart_add_one_port uart_remove_one_port uart_console_write uart_parse_earlycon uart_parse_options uart_set_options uart_get_lsr_info uart_handle_dcd_change uart_handle_cts_change uart_try_toggle_sysrq uart_get_console .. kernel-doc:: include/linux/serial_core.h :identifiers: uart_port_tx_limited uart_port_tx Other notes ----------- It is intended some day to drop the 'unused' entries from uart_port, and allow low level drivers to register their own individual uart_port's with the core. This will allow drivers to use uart_port as a pointer to a structure containing both the uart_port entry with their own extensions, thus:: struct my_port { struct uart_port port; int my_stuff; }; Modem control lines via GPIO ---------------------------- Some helpers are provided in order to set/get modem control lines via GPIO. .. kernel-doc:: drivers/tty/serial/serial_mctrl_gpio.c :identifiers: mctrl_gpio_init mctrl_gpio_free mctrl_gpio_to_gpiod mctrl_gpio_set mctrl_gpio_get mctrl_gpio_enable_ms mctrl_gpio_disable_ms |