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| author | Lukas Wunner <lukas@wunner.de> | 2020-02-28 14:31:06 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-03-07 09:52:02 +0100 |
| commit | 058bc104f7ca5c83d81695ee96f03dbd93bae518 (patch) | |
| tree | a908937e8918956d66a332bc3f860b49aabae31e /include/linux/serial_8250.h | |
| parent | 41a70b7f4734fc4f8982a31c8c505357b4adacaa (diff) | |
| download | lwn-058bc104f7ca5c83d81695ee96f03dbd93bae518.tar.gz lwn-058bc104f7ca5c83d81695ee96f03dbd93bae518.zip | |
serial: 8250: Generalize rs485 software emulation
Commit e490c9144cfa ("tty: Add software emulated RS485 support for 8250")
introduced support to use RTS as an rs485 Transmit Enable signal.
So far the only drivers taking advantage of it are 8250_omap.c and
8250_of.c.
We're about to make use of the feature in 8250_bcm2835aux.c as well.
The bcm2835aux differs from omap chips by inverting the meaning of RTS
in the MCR register. Moreover, omap achieves half-duplex mode by
disabling the RX interrupt and clearing the RX FIFO when TX stops.
The bcm2835aux requires disabling the receiver instead.
Support these behavioral differences by generalizing the rs485 emulation:
Introduce ->rs485_start_tx() and ->rs485_stop_tx() callbacks in struct
uart_8250_port, provide generic implementations containing the existing
code and use them as callbacks in 8250_omap.c and 8250_of.c.
start_tx_rs485() is idempotent in that it recognizes whether RTS is
already asserted. Achieve the same by introducing a tx_stopped flag in
struct uart_8250_em485. This may even perform a little better on arches
where memory access is faster than mmio access.
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Matwey V. Kornilov <matwey@sai.msu.ru>
Link: https://lore.kernel.org/r/5ac0464ae4414708e723a1e0d52b0c1b2bd41b9b.1582895077.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/serial_8250.h')
| -rw-r--r-- | include/linux/serial_8250.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 6a8e8c48c882..0901c2aa366c 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -81,6 +81,7 @@ struct uart_8250_em485 { struct hrtimer stop_tx_timer; /* "rs485 stop tx" timer */ struct hrtimer *active_timer; /* pointer to active timer */ struct uart_8250_port *port; /* for hrtimer callbacks */ + unsigned int tx_stopped:1; /* tx is currently stopped */ }; /* @@ -132,6 +133,8 @@ struct uart_8250_port { void (*dl_write)(struct uart_8250_port *, int); struct uart_8250_em485 *em485; + void (*rs485_start_tx)(struct uart_8250_port *); + void (*rs485_stop_tx)(struct uart_8250_port *); /* Serial port overrun backoff */ struct delayed_work overrun_backoff; |