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serial: Support for RS-485 multipoint addresses

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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 <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220624204210.11112-6-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ilpo Järvinen
2022-06-24 23:42:09 +03:00
committed by Greg Kroah-Hartman
parent ae50bb2752
commit 4f768e9477
6 changed files with 71 additions and 4 deletions
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20
include/uapi/linux/serial.h
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@@ -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];
};
};
};
/*