diff options
Diffstat (limited to 'Documentation/driver-api')
| -rw-r--r-- | Documentation/driver-api/serial/driver.rst | 482 | ||||
| -rw-r--r-- | Documentation/driver-api/serial/serial-rs485.rst | 38 |
2 files changed, 51 insertions, 469 deletions
diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst index 7ef83fd3917b..23c6b956cd90 100644 --- a/Documentation/driver-api/serial/driver.rst +++ b/Documentation/driver-api/serial/driver.rst @@ -25,10 +25,10 @@ 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). +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 +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. @@ -39,7 +39,7 @@ 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 uart_ops listing below.) +are described in the struct uart_ops listing below.) There are two locks. A per-port spinlock, and an overall semaphore. @@ -63,442 +63,20 @@ commonly referred to as the port mutex. uart_ops -------- -The uart_ops structure is the main interface between serial_core and the -hardware specific driver. It contains all the methods to control the -hardware. - - tx_empty(port) - This function tests whether the transmitter fifo and shifter - for the port described by 'port' is empty. If it is empty, - this function should return TIOCSER_TEMT, otherwise return 0. - If the port does not support this operation, then it should - return TIOCSER_TEMT. - - Locking: none. - - Interrupts: caller dependent. - - This call must not sleep - - set_mctrl(port, mctrl) - This function sets the modem control lines for port described - by 'port' to the state described by mctrl. The relevant bits - of mctrl are: - - - TIOCM_RTS RTS signal. - - TIOCM_DTR DTR signal. - - TIOCM_OUT1 OUT1 signal. - - TIOCM_OUT2 OUT2 signal. - - TIOCM_LOOP Set the port into loopback mode. - - If the appropriate bit is set, the signal should be driven - active. If the bit is clear, the signal should be driven - inactive. - - Locking: port->lock taken. - - Interrupts: locally disabled. - - This call must not sleep - - get_mctrl(port) - Returns the current state of modem control inputs. The state - of the outputs should not be returned, since the core keeps - track of their state. The state information should include: - - - TIOCM_CAR state of DCD signal - - TIOCM_CTS state of CTS signal - - TIOCM_DSR state of DSR signal - - TIOCM_RI state of RI signal - - The bit is set if the signal is currently driven active. If - the port does not support CTS, DCD or DSR, the driver should - indicate that the signal is permanently active. If RI is - not available, the signal should not be indicated as active. - - Locking: port->lock taken. - - Interrupts: locally disabled. - - This call must not sleep - - stop_tx(port) - Stop transmitting characters. This might be due to the CTS - line becoming inactive or the tty layer indicating we want - to stop transmission due to an XOFF character. - - The driver should stop transmitting characters as soon as - possible. - - Locking: port->lock taken. - - Interrupts: locally disabled. - - This call must not sleep - - start_tx(port) - Start transmitting characters. - - Locking: port->lock taken. - - Interrupts: locally disabled. - - This call must not sleep - - throttle(port) - Notify the serial driver that input buffers for the line discipline are - close to full, and it should somehow signal that no more characters - should be sent to the serial port. - This will be called only if hardware assisted flow control is enabled. - - Locking: serialized with .unthrottle() and termios modification by the - tty layer. - - unthrottle(port) - Notify the serial driver that characters can now be sent to the serial - port without fear of overrunning the input buffers of the line - disciplines. - - This will be called only if hardware assisted flow control is enabled. - - Locking: serialized with .throttle() and termios modification by the - tty layer. - - send_xchar(port,ch) - Transmit a high priority character, even if the port is stopped. - This is used to implement XON/XOFF flow control and tcflow(). If - the serial driver does not implement this function, the tty core - will append the character to the circular buffer and then call - start_tx() / stop_tx() to flush the data out. - - Do not transmit if ch == '\0' (__DISABLED_CHAR). - - Locking: none. - - Interrupts: caller dependent. - - stop_rx(port) - Stop receiving characters; the port is in the process of - being closed. - - Locking: port->lock taken. - - Interrupts: locally disabled. - - This call must not sleep - - enable_ms(port) - Enable the modem status interrupts. - - This method may be called multiple times. Modem status - interrupts should be disabled when the shutdown method is - called. - - Locking: port->lock taken. - - Interrupts: locally disabled. - - This call must not sleep - - break_ctl(port,ctl) - Control the transmission of a break signal. If ctl is - nonzero, the break signal should be transmitted. The signal - should be terminated when another call is made with a zero - ctl. - - Locking: caller holds tty_port->mutex - - startup(port) - Grab any interrupt resources and initialise any low level driver - state. Enable the port for reception. It should not activate - RTS nor DTR; this will be done via a separate call to set_mctrl. - - This method will only be called when the port is initially opened. - - Locking: port_sem taken. - - Interrupts: globally disabled. - - shutdown(port) - Disable the port, disable any break condition that may be in - effect, and free any interrupt resources. It should not disable - RTS nor DTR; this will have already been done via a separate - call to set_mctrl. - - Drivers must not access port->state once this call has completed. - - This method will only be called when there are no more users of - this port. - - Locking: port_sem taken. - - Interrupts: caller dependent. - - flush_buffer(port) - Flush any write buffers, reset any DMA state and stop any - ongoing DMA transfers. - - This will be called whenever the port->state->xmit circular - buffer is cleared. - - Locking: port->lock taken. - - Interrupts: locally disabled. - - This call must not sleep - - set_termios(port,termios,oldtermios) - Change the port parameters, including word length, parity, stop - bits. Update read_status_mask and ignore_status_mask to indicate - the types of events we are interested in receiving. Relevant - termios->c_cflag bits are: - - CSIZE - - word size - CSTOPB - - 2 stop bits - PARENB - - parity enable - PARODD - - odd parity (when PARENB is in force) - CREAD - - enable reception of characters (if not set, - still receive characters from the port, but - throw them away. - CRTSCTS - - if set, enable CTS status change reporting - CLOCAL - - if not set, enable modem status change - reporting. - - Relevant termios->c_iflag bits are: - - INPCK - - enable frame and parity error events to be - passed to the TTY layer. - BRKINT / PARMRK - - both of these enable break events to be - passed to the TTY layer. - - IGNPAR - - ignore parity and framing errors - IGNBRK - - ignore break errors, If IGNPAR is also - set, ignore overrun errors as well. - - The interaction of the iflag bits is as follows (parity error - given as an example): - - =============== ======= ====== ============================= - Parity error INPCK IGNPAR - =============== ======= ====== ============================= - n/a 0 n/a character received, marked as - TTY_NORMAL - None 1 n/a character received, marked as - TTY_NORMAL - Yes 1 0 character received, marked as - TTY_PARITY - Yes 1 1 character discarded - =============== ======= ====== ============================= - - Other flags may be used (eg, xon/xoff characters) if your - hardware supports hardware "soft" flow control. - - Locking: caller holds tty_port->mutex - - Interrupts: caller dependent. - - This call must not sleep - - set_ldisc(port,termios) - Notifier for discipline change. See ../tty/tty_ldisc.rst. - - Locking: caller holds tty_port->mutex - - pm(port,state,oldstate) - Perform any power management related activities on the specified - port. State indicates the new state (defined by - enum uart_pm_state), oldstate indicates the previous state. - - This function should not be used to grab any resources. - - This will be called when the port is initially opened and finally - closed, except when the port is also the system console. This - will occur even if CONFIG_PM is not set. - - Locking: none. - - Interrupts: caller dependent. - - type(port) - Return a pointer to a string constant describing the specified - port, or return NULL, in which case the string 'unknown' is - substituted. - - Locking: none. - - Interrupts: caller dependent. - - release_port(port) - Release any memory and IO region resources currently in use by - the port. - - Locking: none. - - Interrupts: caller dependent. - - request_port(port) - Request any memory and IO region resources required by the port. - If any fail, no resources should be registered when this function - returns, and it should return -EBUSY on failure. - - Locking: none. - - Interrupts: caller dependent. - - config_port(port,type) - Perform any autoconfiguration steps required for the port. `type` - contains a bit mask of the required configuration. UART_CONFIG_TYPE - indicates that the port requires detection and identification. - port->type should be set to the type found, or PORT_UNKNOWN if - no port was detected. - - UART_CONFIG_IRQ indicates autoconfiguration of the interrupt signal, - which should be probed using standard kernel autoprobing techniques. - This is not necessary on platforms where ports have interrupts - internally hard wired (eg, system on a chip implementations). - - Locking: none. - - Interrupts: caller dependent. - - verify_port(port,serinfo) - Verify the new serial port information contained within serinfo is - suitable for this port type. - - Locking: none. - - Interrupts: caller dependent. - - ioctl(port,cmd,arg) - Perform any port specific IOCTLs. IOCTL commands must be defined - using the standard numbering system found in <asm/ioctl.h> - - Locking: none. - - Interrupts: caller dependent. - - poll_init(port) - Called by kgdb to perform the minimal hardware initialization needed - to support poll_put_char() and poll_get_char(). Unlike ->startup() - this should not request interrupts. - - Locking: tty_mutex and tty_port->mutex taken. - - Interrupts: n/a. - - poll_put_char(port,ch) - Called by kgdb to write a single character directly to the serial - port. It can and should block until there is space in the TX FIFO. - - Locking: none. - - Interrupts: caller dependent. - - This call must not sleep - - poll_get_char(port) - Called by kgdb to read a single character directly from the serial - port. If data is available, it should be returned; otherwise - the function should return NO_POLL_CHAR immediately. - - Locking: none. - - Interrupts: caller dependent. - - This call must not sleep +.. kernel-doc:: include/linux/serial_core.h + :identifiers: uart_ops Other functions --------------- -uart_update_timeout(port,cflag,baud) - Update the FIFO drain timeout, port->timeout, according to the - number of bits, parity, stop bits and baud rate. - - Locking: caller is expected to take port->lock - - Interrupts: n/a - -uart_get_baud_rate(port,termios,old,min,max) - Return the numeric baud rate for the specified termios, taking - account of the special 38400 baud "kludge". The B0 baud rate - is mapped to 9600 baud. - - If the baud rate is not within min..max, then if old is non-NULL, - the original baud rate will be tried. If that exceeds the - min..max constraint, 9600 baud will be returned. termios will - be updated to the baud rate in use. - - Note: min..max must always allow 9600 baud to be selected. - - Locking: caller dependent. - - Interrupts: n/a - -uart_get_divisor(port,baud) - Return the divisor (baud_base / baud) for the specified baud - rate, appropriately rounded. - - If 38400 baud and custom divisor is selected, return the - custom divisor instead. - - Locking: caller dependent. - - Interrupts: n/a - -uart_match_port(port1,port2) - This utility function can be used to determine whether two - uart_port structures describe the same port. - - Locking: n/a - - Interrupts: n/a - -uart_write_wakeup(port) - A driver is expected to call this function when the number of - characters in the transmit buffer have dropped below a threshold. - - Locking: port->lock should be held. - - Interrupts: n/a - -uart_register_driver(drv) - Register a uart driver with the core driver. We in turn register - with the tty layer, and initialise the core driver per-port state. - - drv->port should be NULL, and the per-port structures should be - registered using uart_add_one_port after this call has succeeded. - - Locking: none - - Interrupts: enabled - -uart_unregister_driver() - Remove all references to a driver from the core driver. The low - level driver must have removed all its ports via the - uart_remove_one_port() if it registered them with uart_add_one_port(). - - Locking: none - - Interrupts: enabled - -**uart_suspend_port()** - -**uart_resume_port()** - -**uart_add_one_port()** - -**uart_remove_one_port()** +.. 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 ----------- @@ -519,31 +97,7 @@ Modem control lines via GPIO Some helpers are provided in order to set/get modem control lines via GPIO. -mctrl_gpio_init(port, idx): - This will get the {cts,rts,...}-gpios from device tree if they are - present and request them, set direction etc, and return an - allocated structure. `devm_*` functions are used, so there's no need - to call mctrl_gpio_free(). - As this sets up the irq handling make sure to not handle changes to the - gpio input lines in your driver, too. - -mctrl_gpio_free(dev, gpios): - This will free the requested gpios in mctrl_gpio_init(). - As `devm_*` functions are used, there's generally no need to call - this function. - -mctrl_gpio_to_gpiod(gpios, gidx) - This returns the gpio_desc structure associated to the modem line - index. - -mctrl_gpio_set(gpios, mctrl): - This will sets the gpios according to the mctrl state. - -mctrl_gpio_get(gpios, mctrl): - This will update mctrl with the gpios values. - -mctrl_gpio_enable_ms(gpios): - Enables irqs and handling of changes to the ms lines. - -mctrl_gpio_disable_ms(gpios): - Disables irqs and handling of changes to the ms lines. +.. 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/serial-rs485.rst b/Documentation/driver-api/serial/serial-rs485.rst index 6bc824f948f9..6ebad75c74ed 100644 --- a/Documentation/driver-api/serial/serial-rs485.rst +++ b/Documentation/driver-api/serial/serial-rs485.rst @@ -38,10 +38,14 @@ RS485 Serial Communications 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 in the uart_port structure. The - serial_core calls rs485_config to do the device specific part in response - to TIOCSRS485 and TIOCGRS485 ioctls (see below). The rs485_config callback - receives a pointer to struct serial_rs485. + 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 ======================== @@ -95,7 +99,31 @@ RS485 Serial Communications /* Error handling. See errno. */ } -5. References +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 |