On Wed, Oct 13, 2021 at 1:38 AM Peter Robinson <[email protected]> wrote: > > Hi Tim, > > > 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? > > A feature for overlays landed upstream in May [1], so the 2021,07 > release, so I'm sure there's most of the functionality you require > already upstream. Not sure how a user would specify which of the > variants to use or how it would load it from the FIT but I'm sure the > patch series provides you a good start point. > > Peter > > [1] https://lists.denx.de/pipermail/u-boot/2021-May/448794.html
Peter, Thanks - this is very helpful and is what I was looking for. My plan is to use the hwconfig env var for users to select how they want serial configured. I can use the methods used in the extension_apply function and it seems appropriate for me to put dtbo's on the root filesystem with the dtb's when using this. Best regards, Tim
