From e51e597d9f692cd7d205e3b44bb35ea3b97e7329 Mon Sep 17 00:00:00 2001
From: Baruch Siach <baruch@tkos.co.il>
Date: Thu, 28 Jun 2018 10:25:32 +0300
Subject: [PATCH] dt-bindings: serial: imx: clarify rs485 support usage
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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>
---
Documentation/devicetree/bindings/serial/fsl-imx-uart.txt | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt b/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
index afcfbc34e2434..35957cbf1571e 100644
--- a/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
+++ b/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
@@ -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.