Finally understood how to do it properly, and hence explaining here for the
record.
In my machine configuration, I have this line (that I overlooked):
```
IMAGE_BOOT_FILES ?= "u-boot.${UBOOT_SUFFIX} MLO zImage
am335x-pocketbeagle.dtb"
```
Which says that it should use the `am335x-pocketbeagle` device tree. I
assume that it infers that it should compile `am335x-pocketbeagle.dts` into
`am335x-pocketbeagle.dtb`. Because `am335x-evm` is listed as the default in
the defconfig, I thought it was the one being used. But I was wrong.
I patched `am335x-pocketbeagle.dts` this time and it just worked.
On Thu, Mar 11, 2021 at 11:28 AM Jonas Vautherin <[email protected]>
wrote:
> Hello!
>
> I am using u-boot on a pocketbeagle which, according to "Default Device
> Tree for DT control" in `bitbake -c menuconfig u-boot`, uses am335x-evm,
> which I understand is the file
> in
> ./build/tmp/work/pocketbeagle-poky-linux-gnueabi/u-boot/1_2020.07-r0/git/arch/arm/dts/am335x-evm.dts.
>
> My issue is that this file ends up setting usb1 as `dr_mode = "host"` and
> usb0 as `dr_mode = "otg"`. I would like to use fastboot on my pocketbeagle,
> and therefore set them to `dr_mode = "peripheral"`.
>
> In order to do that, I wrote a .bbappend that does the following:
>
> ```
> FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
>
> SRC_URI += "file://am335x-evm.dts.patch"
> SRC_URI += "file://logging.cfg"
> ```
>
> The patch sets both usb0 and usb1 to `dr_mode = "peripheral"`, while the
> cfg enables logging in u-boot. Because logging is effectively enabled, I
> get that my .bbappend is used. And I can confirm
> that
> ./build/tmp/work/pocketbeagle-poky-linux-gnueabi/u-boot/1_2020.07-r0/git/arch/arm/dts/am335x-evm.dts
> is patched indeed.
>
> However, whatever I do, I can't seem to get that modification in my u-boot
> device tree at runtime, as usb0 always ends up as "otg" and usb1 as "host".
> I have even tried a full clean build where I removed build/tmp and
> cache_sstate.
>
> I cannot really tell if my patched file is actually used or not. For
> instance, if I `bitbake -c cleansstate u-boot`, then `bitbake -c do_patch
> u-boot`, then `rm
> -rf
> ./build/tmp/work/pocketbeagle-poky-linux-gnueabi/u-boot/1_2020.07-r0/git/arch/arm/dts`
> and finally `bitbake u-boot`, it does not complain at all about a missing
> dts file.
>
> What am I missing, and how could I make sure that my patched
> am335x-evm.dts is the device tree being used by my u-boot install?
>
> Best Regards,
> Jonas
>
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