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Diffstat (limited to 'Documentation/driver-api/serial')
| -rw-r--r-- | Documentation/driver-api/serial/driver.rst | 103 | ||||
| -rw-r--r-- | Documentation/driver-api/serial/index.rst | 27 | ||||
| -rw-r--r-- | Documentation/driver-api/serial/serial-iso7816.rst | 90 | ||||
| -rw-r--r-- | Documentation/driver-api/serial/serial-rs485.rst | 131 |
4 files changed, 351 insertions, 0 deletions
diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst new file mode 100644 index 000000000..23c6b956c --- /dev/null +++ b/Documentation/driver-api/serial/driver.rst @@ -0,0 +1,103 @@ +==================== +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 + +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 diff --git a/Documentation/driver-api/serial/index.rst b/Documentation/driver-api/serial/index.rst new file mode 100644 index 000000000..03a55b987 --- /dev/null +++ b/Documentation/driver-api/serial/index.rst @@ -0,0 +1,27 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================== +Support for Serial devices +========================== + +.. toctree:: + :maxdepth: 1 + + + driver + +Serial drivers +============== + +.. toctree:: + :maxdepth: 1 + + serial-iso7816 + serial-rs485 + +.. only:: subproject and html + + Indices + ======= + + * :ref:`genindex` diff --git a/Documentation/driver-api/serial/serial-iso7816.rst b/Documentation/driver-api/serial/serial-iso7816.rst new file mode 100644 index 000000000..d990143de --- /dev/null +++ b/Documentation/driver-api/serial/serial-iso7816.rst @@ -0,0 +1,90 @@ +============================= +ISO7816 Serial Communications +============================= + +1. Introduction +=============== + + ISO/IEC7816 is a series of standards specifying integrated circuit cards (ICC) + also known as smart cards. + +2. Hardware-related considerations +================================== + + Some CPUs/UARTs (e.g., Microchip AT91) contain a built-in mode capable of + handling communication with a smart card. + + For these microcontrollers, the Linux driver should be made capable of + working in both modes, and proper ioctls (see later) should be made + available at user-level to allow switching from one mode to the other, and + vice versa. + +3. Data Structures Already Available in the Kernel +================================================== + + The Linux kernel provides the serial_iso7816 structure (see [1]) to handle + ISO7816 communications. This data structure is used to set and configure + ISO7816 parameters in ioctls. + + Any driver for devices capable of working both as RS232 and ISO7816 should + implement the iso7816_config callback in the uart_port structure. The + serial_core calls iso7816_config to do the device specific part in response + to TIOCGISO7816 and TIOCSISO7816 ioctls (see below). The iso7816_config + callback receives a pointer to struct serial_iso7816. + +4. Usage from user-level +======================== + + From user-level, ISO7816 configuration can be get/set using the previous + ioctls. For instance, to set ISO7816 you can use the following code:: + + #include <linux/serial.h> + + /* Include definition for ISO7816 ioctls: TIOCSISO7816 and TIOCGISO7816 */ + #include <sys/ioctl.h> + + /* Open your specific device (e.g., /dev/mydevice): */ + int fd = open ("/dev/mydevice", O_RDWR); + if (fd < 0) { + /* Error handling. See errno. */ + } + + struct serial_iso7816 iso7816conf; + + /* Reserved fields as to be zeroed */ + memset(&iso7816conf, 0, sizeof(iso7816conf)); + + /* Enable ISO7816 mode: */ + iso7816conf.flags |= SER_ISO7816_ENABLED; + + /* Select the protocol: */ + /* T=0 */ + iso7816conf.flags |= SER_ISO7816_T(0); + /* or T=1 */ + iso7816conf.flags |= SER_ISO7816_T(1); + + /* Set the guard time: */ + iso7816conf.tg = 2; + + /* Set the clock frequency*/ + iso7816conf.clk = 3571200; + + /* Set transmission factors: */ + iso7816conf.sc_fi = 372; + iso7816conf.sc_di = 1; + + if (ioctl(fd_usart, TIOCSISO7816, &iso7816conf) < 0) { + /* Error handling. See errno. */ + } + + /* Use read() and write() syscalls here... */ + + /* Close the device when finished: */ + if (close (fd) < 0) { + /* Error handling. See errno. */ + } + +5. References +============= + + [1] include/uapi/linux/serial.h diff --git a/Documentation/driver-api/serial/serial-rs485.rst b/Documentation/driver-api/serial/serial-rs485.rst new file mode 100644 index 000000000..6ebad75c7 --- /dev/null +++ b/Documentation/driver-api/serial/serial-rs485.rst @@ -0,0 +1,131 @@ +=========================== +RS485 Serial Communications +=========================== + +1. Introduction +=============== + + EIA-485, also known as TIA/EIA-485 or RS-485, is a standard defining the + electrical characteristics of drivers and receivers for use in balanced + digital multipoint systems. + This standard is widely used for communications in industrial automation + because it can be used effectively over long distances and in electrically + noisy environments. + +2. Hardware-related Considerations +================================== + + Some CPUs/UARTs (e.g., Atmel AT91 or 16C950 UART) contain a built-in + half-duplex mode capable of automatically controlling line direction by + toggling RTS or DTR signals. That can be used to control external + half-duplex hardware like an RS485 transceiver or any RS232-connected + half-duplex devices like some modems. + + For these microcontrollers, the Linux driver should be made capable of + working in both modes, and proper ioctls (see later) should be made + available at user-level to allow switching from one mode to the other, and + vice versa. + +3. Data Structures Already Available in the Kernel +================================================== + + The Linux kernel provides the serial_rs485 structure (see [1]) to handle + RS485 communications. This data structure is used to set and configure RS485 + parameters in the platform data and in ioctls. + + The device tree can also provide RS485 boot time parameters (see [2] + for bindings). The driver is in charge of filling this data structure from + the values given by the device tree. + + Any driver for devices capable of working both as RS232 and RS485 should + implement the rs485_config callback and provide rs485_supported in the + uart_port structure. The serial core calls rs485_config to do the device + specific part in response to TIOCSRS485 ioctl (see below). The rs485_config + callback receives a pointer to a sanitizated serial_rs485 structure. The + serial_rs485 userspace provides is sanitized before calling rs485_config + using rs485_supported that indicates what RS485 features the driver supports + for the uart_port. TIOCGRS485 ioctl can be used to read back the + serial_rs485 structure matching to the current configuration. + +4. Usage from user-level +======================== + + From user-level, RS485 configuration can be get/set using the previous + ioctls. For instance, to set RS485 you can use the following code:: + + #include <linux/serial.h> + + /* Include definition for RS485 ioctls: TIOCGRS485 and TIOCSRS485 */ + #include <sys/ioctl.h> + + /* Open your specific device (e.g., /dev/mydevice): */ + int fd = open ("/dev/mydevice", O_RDWR); + if (fd < 0) { + /* Error handling. See errno. */ + } + + struct serial_rs485 rs485conf; + + /* Enable RS485 mode: */ + rs485conf.flags |= SER_RS485_ENABLED; + + /* Set logical level for RTS pin equal to 1 when sending: */ + rs485conf.flags |= SER_RS485_RTS_ON_SEND; + /* or, set logical level for RTS pin equal to 0 when sending: */ + rs485conf.flags &= ~(SER_RS485_RTS_ON_SEND); + + /* Set logical level for RTS pin equal to 1 after sending: */ + rs485conf.flags |= SER_RS485_RTS_AFTER_SEND; + /* or, set logical level for RTS pin equal to 0 after sending: */ + rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND); + + /* Set rts delay before send, if needed: */ + rs485conf.delay_rts_before_send = ...; + + /* Set rts delay after send, if needed: */ + rs485conf.delay_rts_after_send = ...; + + /* Set this flag if you want to receive data even while sending data */ + rs485conf.flags |= SER_RS485_RX_DURING_TX; + + if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) { + /* Error handling. See errno. */ + } + + /* Use read() and write() syscalls here... */ + + /* Close the device when finished: */ + if (close (fd) < 0) { + /* Error handling. See errno. */ + } + +5. Multipoint Addressing +======================== + + The Linux kernel provides addressing mode for multipoint RS-485 serial + communications line. The addressing mode is enabled with SER_RS485_ADDRB + flag in serial_rs485. Struct serial_rs485 has two additional flags and + fields for enabling receive and destination addresses. + + Address mode flags: + - SER_RS485_ADDRB: Enabled addressing mode (sets also ADDRB in termios). + - SER_RS485_ADDR_RECV: Receive (filter) address enabled. + - SER_RS485_ADDR_DEST: Set destination address. + + Address fields (enabled with corresponding SER_RS485_ADDR_* flag): + - addr_recv: Receive address. + - addr_dest: Destination address. + + Once a receive address is set, the communication can occur only with the + particular device and other peers are filtered out. It is left up to the + receiver side to enforce the filtering. Receive address will be cleared + if SER_RS485_ADDR_RECV is not set. + + Note: not all devices supporting RS485 support multipoint addressing. + +6. References +============= + + [1] include/uapi/linux/serial.h + + [2] Documentation/devicetree/bindings/serial/rs485.txt |