[PATCH 0/4] rs485 bus termination GPIO

[Lukas Wunner <lukas@wunner.de>]

Commit e8759ad17d41 ("serial: uapi: Add support for bus termination"),
allowed user space to change rs485 bus termination through a flag in
struct serial_rs485.  But so far only a single driver, 8250_exar.c,
supports the flag:  It hardcodes a GPIO specific to Siemens IOT2040
products.

Provide for a more generic solution:  Define a device tree binding
for an rs485 bus termination GPIO (patch [3/4]), amend the serial core
to retrieve the GPIO from the device tree and amend the default
->rs485_config() callback for 8250 drivers to change the GPIO on
request from user space (patch [4/4]).

Retrieving the GPIO from the device tree may fail, so allow
uart_get_rs485_mode() to return an errno and change all callers
to check for failure (patch [2/4]).

Testing has exposed a bug in the 8250 core if retrieval of the GPIO
initially fails with -EPROBE_DEFER and is later retried.  That bug
is fixed by patch [1/4].


Lukas Wunner (4):
  serial: 8250: Avoid error message on reprobe
  serial: Allow uart_get_rs485_mode() to return errno
  dt-bindings: serial: Add binding for rs485 bus termination GPIO
  serial: 8250: Support rs485 bus termination GPIO

 .../devicetree/bindings/serial/rs485.yaml     |  4 +++
 drivers/tty/serial/8250/8250_core.c           | 16 +++++++---
 drivers/tty/serial/8250/8250_port.c           |  4 +++
 drivers/tty/serial/ar933x_uart.c              |  6 ++--
 drivers/tty/serial/atmel_serial.c             |  6 ++--
 drivers/tty/serial/fsl_lpuart.c               |  5 +++-
 drivers/tty/serial/imx.c                      |  6 +++-
 drivers/tty/serial/omap-serial.c              |  4 ++-
 drivers/tty/serial/serial_core.c              | 30 ++++++++++++++++++-
 drivers/tty/serial/stm32-usart.c              |  8 ++---
 include/linux/serial_core.h                   |  4 ++-
 11 files changed, 76 insertions(+), 17 deletions(-)

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2.26.2