Commit 4f768e94 authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by Greg Kroah-Hartman
Browse files

serial: Support for RS-485 multipoint addresses 



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: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220624204210.11112-6-ilpo.jarvinen@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ae50bb27

Documentation/driver-api/serial/driver.rst

+2 −0
Original line number Diff line number Diff line
@@ -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

Documentation/driver-api/serial/serial-rs485.rst

+25 −1
Original line number Diff line number Diff line
@@ -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

drivers/tty/serial/serial_core.c

+21 −1
Original line number Diff line number Diff line
@@ -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");

drivers/tty/tty_ioctl.c

+4 −0
Original line number Diff line number Diff line
@@ -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);

include/uapi/asm-generic/termbits-common.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */