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dt-bindings: serial: imx: clarify rs485 support usage

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The i.MX UART peripheral uses the RST_B signal as input, and CTS_B as
output. This is just like the DCE role in RS-232. This is true
regardless of the "DTE mode" setting of this peripheral.

As a result, rs485 support hardware must use the CTS_B signal to control
the RS-485 transceiver. This is in contrast to generic rs485 kernel
code, documentation, and DT property names that consistently refer to
the RTS as transceiver control signal.

Add a note in the DT binding document about that, to reduce the
confusion somewhat.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Baruch Siach 2018-06-28 10:25:32 +03:00 committed by Greg Kroah-Hartman
parent 728e74a46f
commit e51e597d9f
1 changed files with 5 additions and 1 deletions
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6
Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
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@ -9,7 +9,11 @@ Optional properties:
- fsl,dte-mode : Indicate the uart works in DTE mode. The uart works
in DCE mode by default.
- rs485-rts-delay, rs485-rts-active-low, rs485-rx-during-tx,
linux,rs485-enabled-at-boot-time: see rs485.txt
linux,rs485-enabled-at-boot-time: see rs485.txt. Note that for RS485
you must enable either the "uart-has-rtscts" or the "rts-gpios"
properties. In case you use "uart-has-rtscts" the signal that controls
the transceiver is actually CTS_B, not RTS_B. CTS_B is always output,
and RTS_B is input, regardless of dte-mode.
Please check Documentation/devicetree/bindings/serial/serial.txt
for the complete list of generic properties.