Greetings,
I'm working on some features for the imx8mm-venice boards I support which depend on making small changes to the dt before booting Linux.
The purpose is not to have any of this apply to the U-Boot controlling dt but instead to the Linux kernel dt applied within ft_board_setup. I could apply these changes with code but it would be way more readable if there was a way to store these as fragments in the FIT image and apply them.
The fragments would be small and have to do with two UART's routed to a multi-protocol RS232/RS485 transceiver that can be used as either of the following: - two tx/rx UART's (the default configuration for my dt's) - one rs232 uart with CTS/RTS flow control - one rs485 uart
Here would be an example dt overlay to apply over the default arch/arm/dts/imx8mm-venice-gw73xx-0x.dts to change it from 2x RS232 UARTS with TX/RX (uart2/uart4) to RS485 half duplex:
/* For RS485 HD: * - UART4_TX is DE for RS485 transmitter * - RS485_EN needs to be pulled high * - RS485_HALF needs to be pulled high * - RS485_TERM enables on-chip termination */ &uart2 { rts-gpios = <&gpio5 29 GPIO_ACTIVE_HIGH>; rs485-term-gpios = <&gpio1 0 GPIO_ACTIVE_HIGH>; };
&uart4 { status = "disabled"; };
&iomuxc { pinctrl-names = "default"; pinctrl-0 = <&pinctrl_hog>;
pinctrl_hog: hoggrp { fsl,pins = < MX8MM_IOMUXC_GPIO1_IO00_GPIO1_IO0 0x40000104 /* RS485_TERM */ MX8MM_IOMUXC_SAI1_RXFS_GPIO4_IO0 0x40000144 /* RS485_EN */ MX8MM_IOMUXC_SAI1_RXD0_GPIO4_IO2 0x40000144 /* RS485_HALF */ >; };
pinctrl_uart2: uart2grp { fsl,pins = < MX8MM_IOMUXC_UART2_RXD_UART2_DCE_RX 0x140 MX8MM_IOMUXC_UART2_TXD_UART2_DCE_TX 0x140 MX8MM_IOMUXC_UART4_TXD_GPIO5_IO29 0x140 >; }; };
Anyone do anything like this before or work with dt fragments/overlays in U-Boot or have any other suggestions?
Best regards,
Tim