Hi Tim,
On 10/7/21 4:07 PM, Tim Harvey wrote:
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?
I had the exact same use case. A couple of prerequisites:
* Compile kernel DTB with __symbols__ ('-@' argument to dtc)
* Enable FIT devicetree overlays in u-boot
- Slightly different CONFIG_s for loading FITs from u-boot or SPL
* Assemble a FIT with overlays in it
I think there's also a way to do apply overlays from the u-boot
commandline, but I never found that to be intuitive.
You might have to specify a "loadaddr=" for the overlays if you're
loading the FIT from u-boot instead of SPL. AFAIR the u-boot FIT loader
is defective in this regard.
Alex
APPENDIX A: Example FIT ITS
/dts-v1/
;/ {
description = "Flu-boot image with overlays";
#address-cells = <1>;
images {
kernel-1 {
description = "Linux kernel";
data = /incbin/("kernel/zImage");
type = "kernel";
arch = "arm";
os = "linux";
compression = "none";
load = <0xc2000040>;
entry = <0xc2000040>;
hash-1 {
algo = "sha256";
};
};
fdt-stm32mp157c-dk2.dtb {
description = "Flattened Device Tree blob";
data = /incbin/("kernel/stm32mp157c-dk2.dtb");
type = "flat_dt";
arch = "arm";
compression = "none";
hash-1 {
algo = "sha256";
};
};
fdt-dk2-can1-enable.dto {
description = "Flattened Device Tree blob";
data = /incbin/("overlays/dk2-can1-enable.dto");
type = "flat_dt";
arch = "arm";
compression = "none";
hash-1 {
algo = "sha256";
};
};
};
configurations {
secure-stm32mp157c-dk2.dtb {
description = "Linux for stm32mp157c-dk2.dtb";
kernel = "kernel-1";
fdt = "fdt-stm32mp157c-dk2.dtb",
"fdt-dk2-can1-enable.dto";
hash-1 {
algo = "sha256";
};
};
};
};
