[PATCH] dt-bindings: serial: imx: clarify rs485 support usage
From: baruch@tkos.co.il (Baruch Siach)
Date: 2018-06-25 07:33:19
Also in:
linux-serial
Subsystem:
open firmware and flattened device tree bindings, the rest, tty layer and serial drivers · Maintainers:
Rob Herring, Krzysztof Kozlowski, Conor Dooley, Linus Torvalds, Greg Kroah-Hartman, Jiri Slaby
The i.MX UART peripheral uses the RST_B signal as input, and CTS_B as output. This is just like the CDE 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 RST 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> --- 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 afcfbc34e243..35957cbf1571 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.
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2.18.0