From 27bc92faa7290804e0d9e9b2482519b703185a8f Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ilpo=20J=C3=A4rvinen?= Date: Fri, 24 Jun 2022 23:42:09 +0300 Subject: [PATCH] serial: Support for RS-485 multipoint addresses MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Add support for RS-485 multipoint addressing using 9th bit [*]. The addressing mode is configured through ->rs485_config(). ADDRB in termios indicates 9th bit addressing mode is enabled. In this mode, 9th bit is used to indicate an address (byte) within the communication line. ADDRB can only be enabled/disabled through ->rs485_config() that is also responsible for setting the destination and receiver (filter) addresses. Add traps to detect unwanted changes to struct serial_rs485 layout using static_assert(). [*] Technically, RS485 is just an electronic spec and does not itself specify the 9th bit addressing mode but 9th bit seems at least "semi-standard" way to do addressing with RS485. Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/20220624204210.11112-6-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- Documentation/driver-api/serial/driver.rst | 2 ++ .../driver-api/serial/serial-rs485.rst | 26 ++++++++++++++++++- drivers/tty/serial/serial_core.c | 22 +++++++++++++++- drivers/tty/tty_ioctl.c | 4 +++ include/uapi/asm-generic/termbits-common.h | 1 + include/uapi/linux/serial.h | 20 ++++++++++++-- 6 files changed, 71 insertions(+), 4 deletions(-) diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst index 1e7ab4142d491..ee1679858aa2a 100644 --- a/Documentation/driver-api/serial/driver.rst +++ b/Documentation/driver-api/serial/driver.rst @@ -261,6 +261,8 @@ hardware. - parity enable PARODD - odd parity (when PARENB is in force) + ADDRB + - address bit (changed through .rs485_config()). CREAD - enable reception of characters (if not set, still receive characters from the port, but diff --git a/Documentation/driver-api/serial/serial-rs485.rst b/Documentation/driver-api/serial/serial-rs485.rst index 00b5d333acbab..6ebad75c74ed9 100644 --- a/Documentation/driver-api/serial/serial-rs485.rst +++ b/Documentation/driver-api/serial/serial-rs485.rst @@ -99,7 +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 diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 2529153c89791..85ef7ef00b824 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1288,6 +1288,17 @@ static int uart_check_rs485_flags(struct uart_port *port, struct serial_rs485 *r if (flags & ~port->rs485_supported->flags) return -EINVAL; + /* Asking for address w/o addressing mode? */ + if (!(rs485->flags & SER_RS485_ADDRB) && + (rs485->flags & (SER_RS485_ADDR_RECV|SER_RS485_ADDR_DEST))) + return -EINVAL; + + /* Address given but not enabled? */ + if (!(rs485->flags & SER_RS485_ADDR_RECV) && rs485->addr_recv) + return -EINVAL; + if (!(rs485->flags & SER_RS485_ADDR_DEST) && rs485->addr_dest) + return -EINVAL; + return 0; } @@ -1343,7 +1354,8 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4 rs485->flags &= supported_flags; /* Return clean padding area to userspace */ - memset(rs485->padding, 0, sizeof(rs485->padding)); + memset(rs485->padding0, 0, sizeof(rs485->padding0)); + memset(rs485->padding1, 0, sizeof(rs485->padding1)); } int uart_rs485_config(struct uart_port *port) @@ -3402,5 +3414,13 @@ int uart_get_rs485_mode(struct uart_port *port) } EXPORT_SYMBOL_GPL(uart_get_rs485_mode); +/* Compile-time assertions for serial_rs485 layout */ +static_assert(offsetof(struct serial_rs485, padding) == + (offsetof(struct serial_rs485, delay_rts_after_send) + sizeof(__u32))); +static_assert(offsetof(struct serial_rs485, padding1) == + offsetof(struct serial_rs485, padding[1])); +static_assert((offsetof(struct serial_rs485, padding[4]) + sizeof(__u32)) == + sizeof(struct serial_rs485)); + MODULE_DESCRIPTION("Serial driver core"); MODULE_LICENSE("GPL"); diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c index adae687f654b5..2a76b330e1089 100644 --- a/drivers/tty/tty_ioctl.c +++ b/drivers/tty/tty_ioctl.c @@ -319,6 +319,8 @@ unsigned char tty_get_frame_size(unsigned int cflag) bits++; if (cflag & PARENB) bits++; + if (cflag & ADDRB) + bits++; return bits; } @@ -353,6 +355,8 @@ int tty_set_termios(struct tty_struct *tty, struct ktermios *new_termios) old_termios = tty->termios; tty->termios = *new_termios; unset_locked_termios(tty, &old_termios); + /* Reset any ADDRB changes, ADDRB is changed through ->rs485_config() */ + tty->termios.c_cflag ^= (tty->termios.c_cflag ^ old_termios.c_cflag) & ADDRB; if (tty->ops->set_termios) tty->ops->set_termios(tty, &old_termios); diff --git a/include/uapi/asm-generic/termbits-common.h b/include/uapi/asm-generic/termbits-common.h index 4d084fe8def54..4a6a79f28b212 100644 --- a/include/uapi/asm-generic/termbits-common.h +++ b/include/uapi/asm-generic/termbits-common.h @@ -46,6 +46,7 @@ typedef unsigned int speed_t; #define EXTA B19200 #define EXTB B38400 +#define ADDRB 0x20000000 /* address bit */ #define CMSPAR 0x40000000 /* mark or space (stick) parity */ #define CRTSCTS 0x80000000 /* flow control */ diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h index fa6b16e5fdd83..cea06924b295d 100644 --- a/include/uapi/linux/serial.h +++ b/include/uapi/linux/serial.h @@ -126,10 +126,26 @@ struct serial_rs485 { #define SER_RS485_TERMINATE_BUS (1 << 5) /* Enable bus termination (if supported) */ + +/* RS-485 addressing mode */ +#define SER_RS485_ADDRB (1 << 6) /* Enable addressing mode */ +#define SER_RS485_ADDR_RECV (1 << 7) /* Receive address filter */ +#define SER_RS485_ADDR_DEST (1 << 8) /* Destination address */ + __u32 delay_rts_before_send; /* Delay before send (milliseconds) */ __u32 delay_rts_after_send; /* Delay after send (milliseconds) */ - __u32 padding[5]; /* Memory is cheap, new structs - are a royal PITA .. */ + + /* The fields below are defined by flags */ + union { + __u32 padding[5]; /* Memory is cheap, new structs are a pain */ + + struct { + __u8 addr_recv; + __u8 addr_dest; + __u8 padding0[2]; + __u32 padding1[4]; + }; + }; }; /* -- 2.39.5