[Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[buildroot]

Hi,

Does anyone have any advice on how to add DTOs needed by libcamera to a 
buildroot build?

We'd like to add Kieran's DTOs

https://git.uk.ideasonboard.com/camera/dt-overlays/src/branch/main/arch/arm64/boot/dts/freescale

to the buildroot default configuration for Debix Model A SBC

https://github.com/buildroot/buildroot/blob/master/configs/polyhex_debix_model_a_defconfig

Ideally we'd also like to add the overlays for the Sony IMX 708 Image 
Sensor used in the RPi V3 camera but these aren't mainline:

https://github.com/raspberrypi/linux/blob/rpi-6.12.y/arch/arm/boot/dts/overlays/imx708-overlay.dts
https://github.com/raspberrypi/linux/blob/rpi-6.12.y/arch/arm/boot/dts/overlays/imx708.dtsi

We're planning to use the Debix Model A SBC or Debix SoM A with SoM A 
I/O board to prototype a new open source wildlife camera for our work in 
conservation of tree dwelling endangered dormice

https://new-homes-for-old-friends.cairnwater.com/

then after field studies with the prototype design a custom board for an 
NXP i.MX 8M Plus SoM.

The analysis for the new open source wildlife camera is here:

https://github.com/William-Robert-Robertson/WildCamera

Will
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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[Fiona Klute via buildroot]

Hi Will!

Am 07.05.25 um 17:41 schrieb buildroot@cairnwater.com:
> Does anyone have any advice on how to add DTOs needed by libcamera to a 
> buildroot build?
> 
> We'd like to add Kieran's DTOs
> 
> https://git.uk.ideasonboard.com/camera/dt-overlays/src/branch/main/arch/ 
> arm64/boot/dts/freescale
> 
> to the buildroot default configuration for Debix Model A SBC
> 
> https://github.com/buildroot/buildroot/blob/master/configs/ 
> polyhex_debix_model_a_defconfig
> 
> Ideally we'd also like to add the overlays for the Sony IMX 708 Image 
> Sensor used in the RPi V3 camera but these aren't mainline:
> 
> https://github.com/raspberrypi/linux/blob/rpi-6.12.y/arch/arm/boot/dts/ 
> overlays/imx708-overlay.dts
> https://github.com/raspberrypi/linux/blob/rpi-6.12.y/arch/arm/boot/dts/ 
> overlays/imx708.dtsi

You can use BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that: Just place the 
DTSOs in the configured directory (with appropriate structure), and 
Buildroot will build them automatically. DTBOs will be in 
${OUTPUT_DIR}/images. From there you'll need to adjust the boot process 
for your board to actually apply the overlay. If you want to send a 
patch, the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board 
directory.

With RPi overlays you'll probably have to adjust the overlays a bit so 
referenced names fit, etc. You're using a different board, and I've seen 
cases where DTS for RPi boards from mainline and RPi kernels use 
different names. But that doesn't change the build process. :-)

Best regards,
Fiona

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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[buildroot]

Hi Fiona,

Thank you very much! That's a big help to know to use 
BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that.

What directory structure is needed for the overlays? Just the DTO files 
in a directory or something more complicated?

> From there you'll need to adjust the boot process for your board to 
> actually apply the overlay. If you want to send a patch, the 
> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board directory.

Thank you very much. I don't know how to do that. What's the best way to 
get the boot process to apply the overlay? I'd heard that it can be done 
by the kernel or by U-Boot but I'm doing this for the first time so I'm 
not sure what I'm doing.

Will


On 2025-05-07 17:41, Fiona Klute via buildroot wrote:
> Hi Will!
> 
> Am 07.05.25 um 17:41 schrieb buildroot@cairnwater.com:
>> Does anyone have any advice on how to add DTOs needed by libcamera to 
>> a buildroot build?
>> 
>> We'd like to add Kieran's DTOs
>> 
>> https://git.uk.ideasonboard.com/camera/dt-overlays/src/branch/main/arch/ 
>> arm64/boot/dts/freescale
>> 
>> to the buildroot default configuration for Debix Model A SBC
>> 
>> https://github.com/buildroot/buildroot/blob/master/configs/ 
>> polyhex_debix_model_a_defconfig
>> 
>> Ideally we'd also like to add the overlays for the Sony IMX 708 Image 
>> Sensor used in the RPi V3 camera but these aren't mainline:
>> 
>> https://github.com/raspberrypi/linux/blob/rpi-6.12.y/arch/arm/boot/dts/ 
>> overlays/imx708-overlay.dts
>> https://github.com/raspberrypi/linux/blob/rpi-6.12.y/arch/arm/boot/dts/ 
>> overlays/imx708.dtsi
> 
> You can use BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that: Just place the 
> DTSOs in the configured directory (with appropriate structure), and 
> Buildroot will build them automatically. DTBOs will be in 
> ${OUTPUT_DIR}/images. From there you'll need to adjust the boot process 
> for your board to actually apply the overlay. If you want to send a 
> patch, the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board 
> directory.
> 
> With RPi overlays you'll probably have to adjust the overlays a bit so 
> referenced names fit, etc. You're using a different board, and I've 
> seen cases where DTS for RPi boards from mainline and RPi kernels use 
> different names. But that doesn't change the build process. :-)
> 
> Best regards,
> Fiona
> 
> _______________________________________________
> buildroot mailing list
> buildroot@buildroot.org
> https://lists.buildroot.org/mailman/listinfo/buildroot
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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[Fiona Klute via buildroot]

Am 07.05.25 um 20:31 schrieb buildroot@cairnwater.com:
> Hi Fiona,
> 
> Thank you very much! That's a big help to know to use 
> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that.
> 
> What directory structure is needed for the overlays? Just the DTO files 
> in a directory or something more complicated?

It's expected to match the structure of the per-arch dts directory in 
the kernel source, with vendor directories. The 
polyhex_debix_model_a_defconfig uses the freescale/imx8mp-debix-model-a 
DTS, so inside your BR2_LINUX_KERNEL_CUSTOM_DTS_DIR you'll probably need 
something like freescale/my-camera.dtso (whatever you want to call your 
DTSOs, the DTBOs will match the source names).

>> From there you'll need to adjust the boot process for your board to 
>> actually apply the overlay. If you want to send a patch, the 
>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board directory.
> 
> Thank you very much. I don't know how to do that. What's the best way to 
> get the boot process to apply the overlay? I'd heard that it can be done 
> by the kernel or by U-Boot but I'm doing this for the first time so I'm 
> not sure what I'm doing.

I'm not familiar with the board, but usually U-Boot will be the right 
place. On some boards (like RPi) the firmware can also do it (only 
useful if U-Boot & kernel then use that FDT), last time I checked 
mainline Linux cannot, but some patched kernels can. There are a number 
of options with U-Boot, which one to pick depends on how you configure 
the boot (at a glance the defconfig seems to use extlinux.conf):

* If you use extlinux.conf, use the "devicetree-overlay" option.
* If you use a boot script, load the overlay and apply it before 
starting the kernel.
* If you use a FIT image, add the overlay to it and the relevant boot 
config defined in it.

See also:
https://docs.u-boot.org/en/latest/develop/distro.html (for extlinux.conf)
https://docs.u-boot.org/en/latest/usage/fdt_overlays.html (for the 
latter 2 options)

Either way you may have to enable overlay support in the U-Boot build 
config (if it isn't by default).

On the Buildroot side you need to make sure that the DTBOs and adjusted 
config get included in the image where U-Boot expects them (depending on 
the boot setup you use), if you need to make adjustments there it'll 
probably be in a post-build or post-image script, or in the genimage config.

The defconfig seems to put everything into the root partition image, so 
it might just work, as long as you use the right path in the U-Boot 
config. Maybe just set BR2_LINUX_KERNEL_CUSTOM_DTS_DIR, build, and see 
if you end up with a DTBO somewhere in your /boot dir. If yes, adjusting 
the U-Boot config to use it should be enough. ;-)

Best regards,
Fiona

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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[buildroot]

Hi Fiona,

Thank you very much - that's an enormous help - I'd have got very 
confused trying to work that out.

I'll study what you said and the links in detail and take more time to 
think about it.

Thank you very much again!

Will

On 2025-05-07 21:06, Fiona Klute wrote:
> Am 07.05.25 um 20:31 schrieb buildroot@cairnwater.com:
>> Hi Fiona,
>> 
>> Thank you very much! That's a big help to know to use 
>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that.
>> 
>> What directory structure is needed for the overlays? Just the DTO 
>> files in a directory or something more complicated?
> 
> It's expected to match the structure of the per-arch dts directory in 
> the kernel source, with vendor directories. The 
> polyhex_debix_model_a_defconfig uses the freescale/imx8mp-debix-model-a 
> DTS, so inside your BR2_LINUX_KERNEL_CUSTOM_DTS_DIR you'll probably 
> need something like freescale/my-camera.dtso (whatever you want to call 
> your DTSOs, the DTBOs will match the source names).
> 
>>> From there you'll need to adjust the boot process for your board to 
>>> actually apply the overlay. If you want to send a patch, the 
>>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board directory.
>> 
>> Thank you very much. I don't know how to do that. What's the best way 
>> to get the boot process to apply the overlay? I'd heard that it can be 
>> done by the kernel or by U-Boot but I'm doing this for the first time 
>> so I'm not sure what I'm doing.
> 
> I'm not familiar with the board, but usually U-Boot will be the right 
> place. On some boards (like RPi) the firmware can also do it (only 
> useful if U-Boot & kernel then use that FDT), last time I checked 
> mainline Linux cannot, but some patched kernels can. There are a number 
> of options with U-Boot, which one to pick depends on how you configure 
> the boot (at a glance the defconfig seems to use extlinux.conf):
> 
> * If you use extlinux.conf, use the "devicetree-overlay" option.
> * If you use a boot script, load the overlay and apply it before 
> starting the kernel.
> * If you use a FIT image, add the overlay to it and the relevant boot 
> config defined in it.
> 
> See also:
> https://docs.u-boot.org/en/latest/develop/distro.html (for 
> extlinux.conf)
> https://docs.u-boot.org/en/latest/usage/fdt_overlays.html (for the 
> latter 2 options)
> 
> Either way you may have to enable overlay support in the U-Boot build 
> config (if it isn't by default).
> 
> On the Buildroot side you need to make sure that the DTBOs and adjusted 
> config get included in the image where U-Boot expects them (depending 
> on the boot setup you use), if you need to make adjustments there it'll 
> probably be in a post-build or post-image script, or in the genimage 
> config.
> 
> The defconfig seems to put everything into the root partition image, so 
> it might just work, as long as you use the right path in the U-Boot 
> config. Maybe just set BR2_LINUX_KERNEL_CUSTOM_DTS_DIR, build, and see 
> if you end up with a DTBO somewhere in your /boot dir. If yes, 
> adjusting the U-Boot config to use it should be enough. ;-)
> 
> Best regards,
> Fiona
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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[buildroot]

Hi Fiona,

Thank you very much!

> It's expected to match the structure of the per-arch dts directory in 
> the kernel source, with vendor directories. The 
> polyhex_debix_model_a_defconfig uses the freescale/imx8mp-debix-model-a 
> DTS, so inside your BR2_LINUX_KERNEL_CUSTOM_DTS_DIR you'll probably 
> need something like freescale/my-camera.dtso (whatever you want to call 
> your DTSOs, the DTBOs will match the source names).

How do I work out where the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR is?

I had a look in the defconfig here:

https://github.com/buildroot/buildroot/blob/master/configs/polyhex_debix_model_a_defconfig

It seems to specify other parameters related to BR2_LINUX_KERNEL but not 
the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR so I got a bit lost trying to work 
out where the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR is and whether it's a 
directory that already exists or a new directory that I should create 
myself?

Is BR2_LINUX_KERNEL_CUSTOM_DTS_DIR something that's not already in the 
defconfig and that I'd have to add to the defconfig?

BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_VERSION=y
BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="6.12.14"
BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y
BR2_LINUX_KERNEL_DTS_SUPPORT=y
BR2_LINUX_KERNEL_INTREE_DTS_NAME="freescale/imx8mp-debix-model-a"
BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME=y
BR2_LINUX_KERNEL_INSTALL_TARGET=y
BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y

> On some boards (like RPi) the firmware can also do it (only useful if 
> U-Boot & kernel then use that FDT), last time I
> checked mainline Linux cannot, but some patched kernels can.

Yes - that's my understanding as well - my knowledge of this is very 
limited but I think maybe RPi can do this and maybe NXP's i.MX Linux can 
do this but I'm not sure whether mainline Linux can do it at the moment.

> There are a number of options with U-Boot, which one to pick
> depends on how you configure the boot (at a glance the defconfig seems 
> to use extlinux.conf):

I'd probably want to stick as close as I can to what's there at the 
moment.

> Either way you may have to enable overlay support in the U-Boot build 
> config (if it isn't by default).

I looked in

https://github.com/buildroot/buildroot/blob/master/configs/polyhex_debix_model_a_defconfig

but couldn't work out how to enable overlay support. Is that usually an 
existing line in the defconfig that should be amended or a new line that 
should be added?

Thank you very much for all your help!

Will

On 2025-05-08 08:46, buildroot@cairnwater.com wrote:
> Hi Fiona,
> 
> Thank you very much - that's an enormous help - I'd have got very 
> confused trying to work that out.
> 
> I'll study what you said and the links in detail and take more time to 
> think about it.
> 
> Thank you very much again!
> 
> Will
> 
> On 2025-05-07 21:06, Fiona Klute wrote:
>> Am 07.05.25 um 20:31 schrieb buildroot@cairnwater.com:
>>> Hi Fiona,
>>> 
>>> Thank you very much! That's a big help to know to use 
>>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that.
>>> 
>>> What directory structure is needed for the overlays? Just the DTO 
>>> files in a directory or something more complicated?
>> 
>> It's expected to match the structure of the per-arch dts directory in 
>> the kernel source, with vendor directories. The 
>> polyhex_debix_model_a_defconfig uses the 
>> freescale/imx8mp-debix-model-a DTS, so inside your 
>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR you'll probably need something like 
>> freescale/my-camera.dtso (whatever you want to call your DTSOs, the 
>> DTBOs will match the source names).
>> 
>>>> From there you'll need to adjust the boot process for your board to 
>>>> actually apply the overlay. If you want to send a patch, the 
>>>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board 
>>>> directory.
>>> 
>>> Thank you very much. I don't know how to do that. What's the best way 
>>> to get the boot process to apply the overlay? I'd heard that it can 
>>> be done by the kernel or by U-Boot but I'm doing this for the first 
>>> time so I'm not sure what I'm doing.
>> 
>> I'm not familiar with the board, but usually U-Boot will be the right 
>> place. On some boards (like RPi) the firmware can also do it (only 
>> useful if U-Boot & kernel then use that FDT), last time I checked 
>> mainline Linux cannot, but some patched kernels can. There are a 
>> number of options with U-Boot, which one to pick depends on how you 
>> configure the boot (at a glance the defconfig seems to use 
>> extlinux.conf):
>> 
>> * If you use extlinux.conf, use the "devicetree-overlay" option.
>> * If you use a boot script, load the overlay and apply it before 
>> starting the kernel.
>> * If you use a FIT image, add the overlay to it and the relevant boot 
>> config defined in it.
>> 
>> See also:
>> https://docs.u-boot.org/en/latest/develop/distro.html (for 
>> extlinux.conf)
>> https://docs.u-boot.org/en/latest/usage/fdt_overlays.html (for the 
>> latter 2 options)
>> 
>> Either way you may have to enable overlay support in the U-Boot build 
>> config (if it isn't by default).
>> 
>> On the Buildroot side you need to make sure that the DTBOs and 
>> adjusted config get included in the image where U-Boot expects them 
>> (depending on the boot setup you use), if you need to make adjustments 
>> there it'll probably be in a post-build or post-image script, or in 
>> the genimage config.
>> 
>> The defconfig seems to put everything into the root partition image, 
>> so it might just work, as long as you use the right path in the U-Boot 
>> config. Maybe just set BR2_LINUX_KERNEL_CUSTOM_DTS_DIR, build, and see 
>> if you end up with a DTBO somewhere in your /boot dir. If yes, 
>> adjusting the U-Boot config to use it should be enough. ;-)
>> 
>> Best regards,
>> Fiona
> _______________________________________________
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> buildroot@buildroot.org
> https://lists.buildroot.org/mailman/listinfo/buildroot
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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[Edgar Bonet via buildroot]

Hello!

On 2025-05-14, Will wrote:
> How do I work out where the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR is?

You may create a directory named "dts" inside
board/<vendor>/<board_name> (or maybe board/<board_name>), put your
device tree files there, inside a vendor subdirectory if that is how the
DTS files are laid out in the kernel, then point
BR2_LINUX_KERNEL_CUSTOM_DTS_DIR to that "dts" directory. See for example

    configs/acmesystems_acqua_a5_256mb_defconfig

Regards,

Edgar.

> I had a look in the defconfig here:
> 
> https://github.com/buildroot/buildroot/blob/master/configs/polyhex_debix_model_a_defconfig
> 
> It seems to specify other parameters related to BR2_LINUX_KERNEL but not the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR so I got a bit lost trying to work out where the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR is and whether it's a directory that already exists or a new directory that I should create myself?
> 
> Is BR2_LINUX_KERNEL_CUSTOM_DTS_DIR something that's not already in the defconfig and that I'd have to add to the defconfig?
> 
> BR2_LINUX_KERNEL=y
> BR2_LINUX_KERNEL_CUSTOM_VERSION=y
> BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="6.12.14"
> BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y
> BR2_LINUX_KERNEL_DTS_SUPPORT=y
> BR2_LINUX_KERNEL_INTREE_DTS_NAME="freescale/imx8mp-debix-model-a"
> BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME=y
> BR2_LINUX_KERNEL_INSTALL_TARGET=y
> BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y
> 
>> On some boards (like RPi) the firmware can also do it (only useful if U-Boot & kernel then use that FDT), last time I
>> checked mainline Linux cannot, but some patched kernels can.
> 
> Yes - that's my understanding as well - my knowledge of this is very limited but I think maybe RPi can do this and maybe NXP's i.MX Linux can do this but I'm not sure whether mainline Linux can do it at the moment.
> 
>> There are a number of options with U-Boot, which one to pick
>> depends on how you configure the boot (at a glance the defconfig seems to use extlinux.conf):
> 
> I'd probably want to stick as close as I can to what's there at the moment.
> 
>> Either way you may have to enable overlay support in the U-Boot build config (if it isn't by default).
> 
> I looked in
> 
> https://github.com/buildroot/buildroot/blob/master/configs/polyhex_debix_model_a_defconfig
> 
> but couldn't work out how to enable overlay support. Is that usually an existing line in the defconfig that should be amended or a new line that should be added?
> 
> Thank you very much for all your help!
> 
> Will
> 
> On 2025-05-08 08:46, buildroot@cairnwater.com wrote:
>> Hi Fiona,
>>
>> Thank you very much - that's an enormous help - I'd have got very confused trying to work that out.
>>
>> I'll study what you said and the links in detail and take more time to think about it.
>>
>> Thank you very much again!
>>
>> Will
>>
>> On 2025-05-07 21:06, Fiona Klute wrote:
>>> Am 07.05.25 um 20:31 schrieb buildroot@cairnwater.com:
>>>> Hi Fiona,
>>>>
>>>> Thank you very much! That's a big help to know to use BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that.
>>>>
>>>> What directory structure is needed for the overlays? Just the DTO files in a directory or something more complicated?
>>>
>>> It's expected to match the structure of the per-arch dts directory in the kernel source, with vendor directories. The polyhex_debix_model_a_defconfig uses the freescale/imx8mp-debix-model-a DTS, so inside your BR2_LINUX_KERNEL_CUSTOM_DTS_DIR you'll probably need something like freescale/my-camera.dtso (whatever you want to call your DTSOs, the DTBOs will match the source names).
>>>
>>>>> From there you'll need to adjust the boot process for your board to actually apply the overlay. If you want to send a patch, the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board directory.
>>>>
>>>> Thank you very much. I don't know how to do that. What's the best way to get the boot process to apply the overlay? I'd heard that it can be done by the kernel or by U-Boot but I'm doing this for the first time so I'm not sure what I'm doing.
>>>
>>> I'm not familiar with the board, but usually U-Boot will be the right place. On some boards (like RPi) the firmware can also do it (only useful if U-Boot & kernel then use that FDT), last time I checked mainline Linux cannot, but some patched kernels can. There are a number of options with U-Boot, which one to pick depends on how you configure the boot (at a glance the defconfig seems to use extlinux.conf):
>>>
>>> * If you use extlinux.conf, use the "devicetree-overlay" option.
>>> * If you use a boot script, load the overlay and apply it before starting the kernel.
>>> * If you use a FIT image, add the overlay to it and the relevant boot config defined in it.
>>>
>>> See also:
>>> https://docs.u-boot.org/en/latest/develop/distro.html (for extlinux.conf)
>>> https://docs.u-boot.org/en/latest/usage/fdt_overlays.html (for the latter 2 options)
>>>
>>> Either way you may have to enable overlay support in the U-Boot build config (if it isn't by default).
>>>
>>> On the Buildroot side you need to make sure that the DTBOs and adjusted config get included in the image where U-Boot expects them (depending on the boot setup you use), if you need to make adjustments there it'll probably be in a post-build or post-image script, or in the genimage config.
>>>
>>> The defconfig seems to put everything into the root partition image, so it might just work, as long as you use the right path in the U-Boot config. Maybe just set BR2_LINUX_KERNEL_CUSTOM_DTS_DIR, build, and see if you end up with a DTBO somewhere in your /boot dir. If yes, adjusting the U-Boot config to use it should be enough. ;-)
>>>
>>> Best regards,
>>> Fiona
>> _______________________________________________
>> buildroot mailing list
>> buildroot@buildroot.org
>> https://lists.buildroot.org/mailman/listinfo/buildroot
> _______________________________________________
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> https://lists.buildroot.org/mailman/listinfo/buildroot

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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[buildroot]

Hello Edgar!

Thank you very much!

I see that in acmesystems defconfig :-)

https://github.com/buildroot/buildroot/blob/master/configs/acmesystems_acqua_a5_256mb_defconfig

I hadn't understood that I could add lines to the defonfig file.

What's the best way for me to keep my changes separate from the 
underlying defconfig? Should I write a short config file that inherits 
the defconfig and applies my changes?

Thank you very much for your help!

Will

On 2025-05-14 19:59, Edgar Bonet wrote:
> Hello!
> 
> On 2025-05-14, Will wrote:
>> How do I work out where the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR is?
> 
> You may create a directory named "dts" inside
> board/<vendor>/<board_name> (or maybe board/<board_name>), put your
> device tree files there, inside a vendor subdirectory if that is how 
> the
> DTS files are laid out in the kernel, then point
> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR to that "dts" directory. See for 
> example
> 
>     configs/acmesystems_acqua_a5_256mb_defconfig
> 
> Regards,
> 
> Edgar.
> 
>> I had a look in the defconfig here:
>> 
>> https://github.com/buildroot/buildroot/blob/master/configs/polyhex_debix_model_a_defconfig
>> 
>> It seems to specify other parameters related to BR2_LINUX_KERNEL but 
>> not the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR so I got a bit lost trying to 
>> work out where the BR2_LINUX_KERNEL_CUSTOM_DTS_DIR is and whether it's 
>> a directory that already exists or a new directory that I should 
>> create myself?
>> 
>> Is BR2_LINUX_KERNEL_CUSTOM_DTS_DIR something that's not already in the 
>> defconfig and that I'd have to add to the defconfig?
>> 
>> BR2_LINUX_KERNEL=y
>> BR2_LINUX_KERNEL_CUSTOM_VERSION=y
>> BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="6.12.14"
>> BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y
>> BR2_LINUX_KERNEL_DTS_SUPPORT=y
>> BR2_LINUX_KERNEL_INTREE_DTS_NAME="freescale/imx8mp-debix-model-a"
>> BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME=y
>> BR2_LINUX_KERNEL_INSTALL_TARGET=y
>> BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y
>> 
>>> On some boards (like RPi) the firmware can also do it (only useful if 
>>> U-Boot & kernel then use that FDT), last time I
>>> checked mainline Linux cannot, but some patched kernels can.
>> 
>> Yes - that's my understanding as well - my knowledge of this is very 
>> limited but I think maybe RPi can do this and maybe NXP's i.MX Linux 
>> can do this but I'm not sure whether mainline Linux can do it at the 
>> moment.
>> 
>>> There are a number of options with U-Boot, which one to pick
>>> depends on how you configure the boot (at a glance the defconfig 
>>> seems to use extlinux.conf):
>> 
>> I'd probably want to stick as close as I can to what's there at the 
>> moment.
>> 
>>> Either way you may have to enable overlay support in the U-Boot build 
>>> config (if it isn't by default).
>> 
>> I looked in
>> 
>> https://github.com/buildroot/buildroot/blob/master/configs/polyhex_debix_model_a_defconfig
>> 
>> but couldn't work out how to enable overlay support. Is that usually 
>> an existing line in the defconfig that should be amended or a new line 
>> that should be added?
>> 
>> Thank you very much for all your help!
>> 
>> Will
>> 
>> On 2025-05-08 08:46, buildroot@cairnwater.com wrote:
>>> Hi Fiona,
>>> 
>>> Thank you very much - that's an enormous help - I'd have got very 
>>> confused trying to work that out.
>>> 
>>> I'll study what you said and the links in detail and take more time 
>>> to think about it.
>>> 
>>> Thank you very much again!
>>> 
>>> Will
>>> 
>>> On 2025-05-07 21:06, Fiona Klute wrote:
>>>> Am 07.05.25 um 20:31 schrieb buildroot@cairnwater.com:
>>>>> Hi Fiona,
>>>>> 
>>>>> Thank you very much! That's a big help to know to use 
>>>>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR for that.
>>>>> 
>>>>> What directory structure is needed for the overlays? Just the DTO 
>>>>> files in a directory or something more complicated?
>>>> 
>>>> It's expected to match the structure of the per-arch dts directory 
>>>> in the kernel source, with vendor directories. The 
>>>> polyhex_debix_model_a_defconfig uses the 
>>>> freescale/imx8mp-debix-model-a DTS, so inside your 
>>>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR you'll probably need something like 
>>>> freescale/my-camera.dtso (whatever you want to call your DTSOs, the 
>>>> DTBOs will match the source names).
>>>> 
>>>>>> From there you'll need to adjust the boot process for your board 
>>>>>> to actually apply the overlay. If you want to send a patch, the 
>>>>>> BR2_LINUX_KERNEL_CUSTOM_DTS_DIR should be inside the board 
>>>>>> directory.
>>>>> 
>>>>> Thank you very much. I don't know how to do that. What's the best 
>>>>> way to get the boot process to apply the overlay? I'd heard that it 
>>>>> can be done by the kernel or by U-Boot but I'm doing this for the 
>>>>> first time so I'm not sure what I'm doing.
>>>> 
>>>> I'm not familiar with the board, but usually U-Boot will be the 
>>>> right place. On some boards (like RPi) the firmware can also do it 
>>>> (only useful if U-Boot & kernel then use that FDT), last time I 
>>>> checked mainline Linux cannot, but some patched kernels can. There 
>>>> are a number of options with U-Boot, which one to pick depends on 
>>>> how you configure the boot (at a glance the defconfig seems to use 
>>>> extlinux.conf):
>>>> 
>>>> * If you use extlinux.conf, use the "devicetree-overlay" option.
>>>> * If you use a boot script, load the overlay and apply it before 
>>>> starting the kernel.
>>>> * If you use a FIT image, add the overlay to it and the relevant 
>>>> boot config defined in it.
>>>> 
>>>> See also:
>>>> https://docs.u-boot.org/en/latest/develop/distro.html (for 
>>>> extlinux.conf)
>>>> https://docs.u-boot.org/en/latest/usage/fdt_overlays.html (for the 
>>>> latter 2 options)
>>>> 
>>>> Either way you may have to enable overlay support in the U-Boot 
>>>> build config (if it isn't by default).
>>>> 
>>>> On the Buildroot side you need to make sure that the DTBOs and 
>>>> adjusted config get included in the image where U-Boot expects them 
>>>> (depending on the boot setup you use), if you need to make 
>>>> adjustments there it'll probably be in a post-build or post-image 
>>>> script, or in the genimage config.
>>>> 
>>>> The defconfig seems to put everything into the root partition image, 
>>>> so it might just work, as long as you use the right path in the 
>>>> U-Boot config. Maybe just set BR2_LINUX_KERNEL_CUSTOM_DTS_DIR, 
>>>> build, and see if you end up with a DTBO somewhere in your /boot 
>>>> dir. If yes, adjusting the U-Boot config to use it should be enough. 
>>>> ;-)
>>>> 
>>>> Best regards,
>>>> Fiona
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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[Fiona Klute via buildroot]

Hi Will!

Am 15.05.25 um 18:11 schrieb buildroot@cairnwater.com:
> I see that in acmesystems defconfig :-)
> 
> https://github.com/buildroot/buildroot/blob/master/configs/ 
> acmesystems_acqua_a5_256mb_defconfig
> 
> I hadn't understood that I could add lines to the defonfig file.
> 
> What's the best way for me to keep my changes separate from the 
> underlying defconfig? Should I write a short config file that inherits 
> the defconfig and applies my changes?

The approach I usually use is to create a custom defconfig, and maintain 
that in an external tree (assuming it's a customized one, not a basic 
one that could be contributed to Buildroot).

Usually you shouldn't need to modify the defconfig file by hand, instead 
just use "make nconfig" (or "make menuconfig", etc., whichever you 
prefer) to adjust your config, change BR2_DEFCONFIG to whatever location 
you want, and run "make savedefconfig" to create the defconfig file.

Best regards,
Fiona

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Re: [Buildroot] Adding Device Tree Overlays for MIPI-CSI2 Camera and libcamera to a buildroot Build

[Fiona Klute via buildroot]

Am 14.05.25 um 19:36 schrieb buildroot@cairnwater.com:
>> Either way you may have to enable overlay support in the U-Boot build 
>> config (if it isn't by default).
> 
> I looked in
> 
> https://github.com/buildroot/buildroot/blob/master/configs/ 
> polyhex_debix_model_a_defconfig
> 
> but couldn't work out how to enable overlay support. Is that usually an 
> existing line in the defconfig that should be amended or a new line that 
> should be added?

U-Boot build config is separate from Buildroot config. In your Buildroot 
config you can either choose a U-Boot defconfig (part of the U-Boot 
sources) to use, or set a custom U-Boot (def-)config file to use. There 
are also make commands to open the U-Boot config editor and save a 
U-Boot defconfig (same idea as saving a custom Buildroot defconfig). The 
same applies for the Linux kernel and a few other components. See 
"Configuration of other components" in the docs, it lists both make 
commands and config options:
https://nightly.buildroot.org/#_configuration_of_other_components

Mind that I wrote you *may* need to enable device tree overlay support 
because I don't know all the U-Boot defconfigs, it's very well possible 
that the one for your board already enables it by default and you don't 
need to change a thing in that regard.

Best regards,
Fiona

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