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Diffstat (limited to '')
| -rw-r--r-- | Documentation/driver-api/serial/serial-rs485.rst | 38 |
1 files changed, 33 insertions, 5 deletions
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 |