linux-kernel - [PATCH v2 07/10] arm64: dts: imx8mp-skov: configure uart1 for RS485

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Message-Id: <20250106-skov-dt-updates-v2-7-4504d3f00ecb@pengutronix.de>
Date: Mon, 06 Jan 2025 17:06:42 +0100
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
 Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>, 
 Oleksij Rempel <o.rempel@...gutronix.de>
Cc: devicetree@...r.kernel.org, imx@...ts.linux.dev, 
 Frank Li <Frank.li@....com>, linux-arm-kernel@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, kernel@...gutronix.de, 
 Ahmad Fatoum <a.fatoum@...gutronix.de>
Subject: [PATCH v2 07/10] arm64: dts: imx8mp-skov: configure uart1 for
 RS485

uart1 TX, RX and RTS signals go off the base board and to a RS485
transceiver. Describe this in the device tree.

Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
---
v1 -> v2:
  - no change
---
 arch/arm64/boot/dts/freescale/imx8mp-skov-reva.dtsi | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/boot/dts/freescale/imx8mp-skov-reva.dtsi b/arch/arm64/boot/dts/freescale/imx8mp-skov-reva.dtsi
index 7ae686d37ddaca7a323e2cb1ec7d807c2e3bd3f5..bce23d62cd277b89ec9ce5ed3651cfe787987158 100644
--- a/arch/arm64/boot/dts/freescale/imx8mp-skov-reva.dtsi
+++ b/arch/arm64/boot/dts/freescale/imx8mp-skov-reva.dtsi
@@ -404,6 +404,13 @@ &uart1 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_uart1>;
 	status = "okay";
+	/*
+	 * While there is no CTS line, the property "uart-has-rtscts" is still
+	 * the right thing to do to enable the UART to do RS485. In RS485-Mode
+	 * CTS isn't used anyhow and there is no dedicated property
+	 * "uart-has-rts-but-no-cts".
+	 */
+	uart-has-rtscts;
 };
 
 &uart2 {
@@ -618,6 +625,8 @@ pinctrl_uart1: uart1grp {
 			MX8MP_IOMUXC_UART1_RXD__UART1_DCE_RX			0x140
 			MX8MP_IOMUXC_UART1_TXD__UART1_DCE_TX			0x140
 			MX8MP_IOMUXC_UART3_RXD__UART1_DTE_RTS			0x140
+			/* CTS pin is not connected, but needed as workaround */
+			MX8MP_IOMUXC_UART3_TXD__UART1_DTE_CTS			0x140
 		>;
 	};
 

-- 
2.39.5