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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/driver-api/serial
parentInitial commit. (diff)
downloadlinux-upstream.tar.xz
linux-upstream.zip
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r--Documentation/driver-api/serial/driver.rst103
-rw-r--r--Documentation/driver-api/serial/index.rst27
-rw-r--r--Documentation/driver-api/serial/serial-iso7816.rst90
-rw-r--r--Documentation/driver-api/serial/serial-rs485.rst131
4 files changed, 351 insertions, 0 deletions
diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst
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+++ 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