107 lines
3.3 KiB
ReStructuredText
107 lines
3.3 KiB
ReStructuredText
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====================
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Low Level Serial API
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====================
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This document is meant as a brief overview of some aspects of the new serial
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driver. It is not complete, any questions you have should be directed to
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<rmk@arm.linux.org.uk>
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The reference implementation is contained within amba-pl011.c.
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Low Level Serial Hardware Driver
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--------------------------------
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The low level serial hardware driver is responsible for supplying port
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information (defined by uart_port) and a set of control methods (defined
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by uart_ops) to the core serial driver. The low level driver is also
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responsible for handling interrupts for the port, and providing any
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console support.
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Console Support
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---------------
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The serial core provides a few helper functions. This includes identifying
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the correct port structure (via uart_get_console()) and decoding command line
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arguments (uart_parse_options()).
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There is also a helper function (uart_console_write()) which performs a
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character by character write, translating newlines to CRLF sequences.
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Driver writers are recommended to use this function rather than implementing
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their own version.
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Locking
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-------
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It is the responsibility of the low level hardware driver to perform the
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necessary locking using port->lock. There are some exceptions (which
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are described in the struct uart_ops listing below.)
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There are two locks. A per-port spinlock, and an overall semaphore.
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From the core driver perspective, the port->lock locks the following
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data::
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port->mctrl
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port->icount
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port->state->xmit.head (circ_buf->head)
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port->state->xmit.tail (circ_buf->tail)
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The low level driver is free to use this lock to provide any additional
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locking.
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The port_sem semaphore is used to protect against ports being added/
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removed or reconfigured at inappropriate times. Since v2.6.27, this
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semaphore has been the 'mutex' member of the tty_port struct, and
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commonly referred to as the port mutex.
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uart_ops
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--------
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.. kernel-doc:: include/linux/serial_core.h
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:identifiers: uart_ops
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Other functions
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---------------
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.. kernel-doc:: drivers/tty/serial/serial_core.c
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:identifiers: uart_update_timeout uart_get_baud_rate uart_get_divisor
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uart_match_port uart_write_wakeup uart_register_driver
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uart_unregister_driver uart_suspend_port uart_resume_port
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uart_add_one_port uart_remove_one_port uart_console_write
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uart_parse_earlycon uart_parse_options uart_set_options
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uart_get_lsr_info uart_handle_dcd_change uart_handle_cts_change
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uart_try_toggle_sysrq uart_get_console
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.. kernel-doc:: include/linux/serial_core.h
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:identifiers: uart_port_tx_limited uart_port_tx
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Other notes
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-----------
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It is intended some day to drop the 'unused' entries from uart_port, and
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allow low level drivers to register their own individual uart_port's with
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the core. This will allow drivers to use uart_port as a pointer to a
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structure containing both the uart_port entry with their own extensions,
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thus::
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struct my_port {
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struct uart_port port;
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int my_stuff;
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};
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Modem control lines via GPIO
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----------------------------
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Some helpers are provided in order to set/get modem control lines via GPIO.
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.. kernel-doc:: drivers/tty/serial/serial_mctrl_gpio.c
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:identifiers: mctrl_gpio_init mctrl_gpio_free mctrl_gpio_to_gpiod
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mctrl_gpio_set mctrl_gpio_get mctrl_gpio_enable_ms
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mctrl_gpio_disable_ms
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