From: Eberhard Stoll Date: Mon, 21 Jul 2025 10:05:37 +0000 (+0200) Subject: arm64: dts: imx8mm-kontron: Use GPIO for RS485 transceiver control X-Git-Tag: v6.18-rc1~147^2~20^2~64 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=371a63c1920112524cc88b585113ffc664a19391;p=thirdparty%2Fkernel%2Flinux.git arm64: dts: imx8mm-kontron: Use GPIO for RS485 transceiver control For this IP the correct control of the CTS signal for transceiver direction switching is difficult and - maybe also buggy - in the driver. Especially the bootup requires special handling for most hardware implementations. Therefore we simply use a GPIO now, which is fully under software control and which is not problematic on bootup. Signed-off-by: Eberhard Stoll Signed-off-by: Frieder Schrempf Signed-off-by: Shawn Guo --- diff --git a/arch/arm64/boot/dts/freescale/imx8mm-kontron-bl.dts b/arch/arm64/boot/dts/freescale/imx8mm-kontron-bl.dts index d16490d876874..e756fe5db56b6 100644 --- a/arch/arm64/boot/dts/freescale/imx8mm-kontron-bl.dts +++ b/arch/arm64/boot/dts/freescale/imx8mm-kontron-bl.dts @@ -268,8 +268,16 @@ &uart2 { pinctrl-names = "default"; pinctrl-0 = <&pinctrl_uart2>; + /* + * During bootup the CTS needs to stay LOW, which is only possible if this + * pin is controlled by a GPIO. The UART IP always sets CTS to HIGH if not + * running. So using 'uart-has-rtscts' is not a good choice here! There are + * workarounds for this, but they introduce unnecessary complexity and are + * therefore avoided here. For more information about this see: + * https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=79d0224f6bf296d04cd843cfc49921b19c97bb09 + */ + rts-gpios = <&gpio4 29 GPIO_ACTIVE_HIGH>; linux,rs485-enabled-at-boot-time; - uart-has-rtscts; status = "okay"; }; @@ -439,7 +447,7 @@ MX8MM_IOMUXC_SAI3_TXFS_UART2_DCE_RX 0x0 MX8MM_IOMUXC_SAI3_TXC_UART2_DCE_TX 0x0 MX8MM_IOMUXC_SAI3_RXD_UART2_DCE_RTS_B 0x0 - MX8MM_IOMUXC_SAI3_RXC_UART2_DCE_CTS_B 0x0 + MX8MM_IOMUXC_SAI3_RXC_GPIO4_IO29 0x19 >; };