[Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Edgar Bonet]

Since Linux 6.12, the Buildroot option BR2_LINUX_KERNEL_CUSTOM_DTS_PATH
does not work as expected on arm, arm64, mips and ricv.[1] These are the
architectures that store the in-tree DTS files in vendor-specific
subdirectories of arch/$ARCH/boot/dts/.

BR2_LINUX_KERNEL_CUSTOM_DTS_PATH was introduced in Buildroot 2012.08
(commit 69fc497df0ae "Rework support for the device tree"). At the time,
the kernel kept all in-tree DTS files directly in arch/$ARCH/boot/dts/,
and this is where Buildroot drops the user's custom DTS. Vendor-specific
subdirectories appeared in Linux v3.19 for the arm64 architecture, and
this scheme was later adopted by mips, riscv and arm.

For these architectures, Linux 6.12 (commit e7e2941300d2, "kbuild: split
device tree build rules into scripts/Makefile.dtbs") made the DTB build
infrastructure incompatible with the way
BR2_LINUX_KERNEL_CUSTOM_DTS_PATH is implemented. This infrastructure now
expects all DTS files to be in vendor-specific subdirectories on the
architectures that use this scheme. Fulfilling this kernel expectation
would require a new configuration parameter for the name of the
appropriate vendor subdirectory. It would also require changing the
relative paths to included .dtsi files.

Let's add instead a rule to the top dts/Makefile for each DTB we want to
build. This avoids breaking user's out-of-tree configurations.

[1] https://lists.buildroot.org/pipermail/buildroot/2024-October/765463.html

Reported-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>
---
Changes v2 -> v3:
  - note, in the comment and in the log message, that this issue only
    affects some architectures
  - expand the log message with some historical context
These changes were suggested by Romain Naour.

Changes v1 -> v2:
  - define a hook for LINUX_POST_PATCH_HOOKS and LINUX_POST_RSYNC_HOOKS
    instead of modifying LINUX_BUILD_CMDS
  - use $(patsubst %.dts,%.dtb,$(dts)) instead of $(dts:%.dts=%.dtb)
both changes suggested by Arnout Vandecappelle.

This was build-tested with an Acqua defconfig,
in the same manner as v2:

    # Test with an old kernel: v6.6.30
    make acmesystems_acqua_a5_512mb_defconfig
    make linux

    # Test with a new kernel: v6.12.8
    make linux-dirclean
    git am bump_Acqua_kernel_to_v6.12.8.patch
    make acmesystems_acqua_a5_512mb_defconfig
    make linux

    # Test the OVERRIDE_SRCDIR case.
    make linux-dirclean
    git -C $HOME/src/linux checkout v6.12.8
    echo "LINUX_OVERRIDE_SRCDIR = $HOME/src/linux" > local.mk
    make acmesystems_acqua_a5_512mb_defconfig
    make linux
---
 linux/linux.mk | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/linux/linux.mk b/linux/linux.mk
index 12699b8ee4..e6e8a3c3bc 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -327,6 +327,17 @@ define LINUX_TRY_PATCH_TIMECONST
 endef
 LINUX_POST_PATCH_HOOKS += LINUX_TRY_PATCH_TIMECONST
 
+# On some architectures, kernels 6.12+ won't compile the custom DTS
+# files we drop into arch/$ARCH/boot/dts unless we add specific rules to
+# that directory's Makefile.
+define LINUX_ADD_DTB_MAKE_RULES
+	$(foreach dts,$(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_DTS_PATH)), \
+		echo "dtb-y += $(patsubst %.dts,%.dtb,$(notdir $(dts)))" >> $(LINUX_ARCH_PATH)/boot/dts/Makefile
+	)
+endef
+LINUX_POST_PATCH_HOOKS += LINUX_ADD_DTB_MAKE_RULES
+LINUX_POST_RSYNC_HOOKS += LINUX_ADD_DTB_MAKE_RULES
+
 LINUX_KERNEL_CUSTOM_LOGO_PATH = $(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_LOGO_PATH))
 ifneq ($(LINUX_KERNEL_CUSTOM_LOGO_PATH),)
 LINUX_DEPENDENCIES += host-imagemagick
-- 
2.34.1
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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Romain Naour via buildroot]

Hi Edgar, All,

Le 03/01/2025 à 15:33, Edgar Bonet a écrit :
> Since Linux 6.12, the Buildroot option BR2_LINUX_KERNEL_CUSTOM_DTS_PATH
> does not work as expected on arm, arm64, mips and ricv.[1] These are the
> architectures that store the in-tree DTS files in vendor-specific
> subdirectories of arch/$ARCH/boot/dts/.
> 
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH was introduced in Buildroot 2012.08
> (commit 69fc497df0ae "Rework support for the device tree"). At the time,
> the kernel kept all in-tree DTS files directly in arch/$ARCH/boot/dts/,
> and this is where Buildroot drops the user's custom DTS. Vendor-specific
> subdirectories appeared in Linux v3.19 for the arm64 architecture, and
> this scheme was later adopted by mips, riscv and arm.
> 
> For these architectures, Linux 6.12 (commit e7e2941300d2, "kbuild: split
> device tree build rules into scripts/Makefile.dtbs") made the DTB build
> infrastructure incompatible with the way
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH is implemented. This infrastructure now
> expects all DTS files to be in vendor-specific subdirectories on the
> architectures that use this scheme. Fulfilling this kernel expectation
> would require a new configuration parameter for the name of the
> appropriate vendor subdirectory. It would also require changing the
> relative paths to included .dtsi files.
> 
> Let's add instead a rule to the top dts/Makefile for each DTB we want to
> build. This avoids breaking user's out-of-tree configurations.

Thanks for the detailed commit log!

I'll wait for feedback from other maintainers and for testing tags.

Reviewed-by: Romain Naour <romain.naour@smile.fr>

Best regards,
Romain


> 
> [1] https://lists.buildroot.org/pipermail/buildroot/2024-October/765463.html
> 
> Reported-by: Chris Packham <judge.packham@gmail.com>
> Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>
> ---
> Changes v2 -> v3:
>   - note, in the comment and in the log message, that this issue only
>     affects some architectures
>   - expand the log message with some historical context
> These changes were suggested by Romain Naour.
> 
> Changes v1 -> v2:
>   - define a hook for LINUX_POST_PATCH_HOOKS and LINUX_POST_RSYNC_HOOKS
>     instead of modifying LINUX_BUILD_CMDS
>   - use $(patsubst %.dts,%.dtb,$(dts)) instead of $(dts:%.dts=%.dtb)
> both changes suggested by Arnout Vandecappelle.
> 
> This was build-tested with an Acqua defconfig,
> in the same manner as v2:
> 
>     # Test with an old kernel: v6.6.30
>     make acmesystems_acqua_a5_512mb_defconfig
>     make linux
> 
>     # Test with a new kernel: v6.12.8
>     make linux-dirclean
>     git am bump_Acqua_kernel_to_v6.12.8.patch
>     make acmesystems_acqua_a5_512mb_defconfig
>     make linux
> 
>     # Test the OVERRIDE_SRCDIR case.
>     make linux-dirclean
>     git -C $HOME/src/linux checkout v6.12.8
>     echo "LINUX_OVERRIDE_SRCDIR = $HOME/src/linux" > local.mk
>     make acmesystems_acqua_a5_512mb_defconfig
>     make linux
> ---
>  linux/linux.mk | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/linux/linux.mk b/linux/linux.mk
> index 12699b8ee4..e6e8a3c3bc 100644
> --- a/linux/linux.mk
> +++ b/linux/linux.mk
> @@ -327,6 +327,17 @@ define LINUX_TRY_PATCH_TIMECONST
>  endef
>  LINUX_POST_PATCH_HOOKS += LINUX_TRY_PATCH_TIMECONST
>  
> +# On some architectures, kernels 6.12+ won't compile the custom DTS
> +# files we drop into arch/$ARCH/boot/dts unless we add specific rules to
> +# that directory's Makefile.
> +define LINUX_ADD_DTB_MAKE_RULES
> +	$(foreach dts,$(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_DTS_PATH)), \
> +		echo "dtb-y += $(patsubst %.dts,%.dtb,$(notdir $(dts)))" >> $(LINUX_ARCH_PATH)/boot/dts/Makefile
> +	)
> +endef
> +LINUX_POST_PATCH_HOOKS += LINUX_ADD_DTB_MAKE_RULES
> +LINUX_POST_RSYNC_HOOKS += LINUX_ADD_DTB_MAKE_RULES
> +
>  LINUX_KERNEL_CUSTOM_LOGO_PATH = $(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_LOGO_PATH))
>  ifneq ($(LINUX_KERNEL_CUSTOM_LOGO_PATH),)
>  LINUX_DEPENDENCIES += host-imagemagick

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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Kilian Zinnecker via buildroot]

On Friday, 3 January 2025 15:33:01 CET Edgar Bonet wrote:
> Since Linux 6.12, the Buildroot option BR2_LINUX_KERNEL_CUSTOM_DTS_PATH
> does not work as expected on arm, arm64, mips and ricv.[1] These are the
> architectures that store the in-tree DTS files in vendor-specific
> subdirectories of arch/$ARCH/boot/dts/.
> 
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH was introduced in Buildroot 2012.08
> (commit 69fc497df0ae "Rework support for the device tree"). At the time,
> the kernel kept all in-tree DTS files directly in arch/$ARCH/boot/dts/,
> and this is where Buildroot drops the user's custom DTS. Vendor-specific
> subdirectories appeared in Linux v3.19 for the arm64 architecture, and
> this scheme was later adopted by mips, riscv and arm.
> 
> For these architectures, Linux 6.12 (commit e7e2941300d2, "kbuild: split
> device tree build rules into scripts/Makefile.dtbs") made the DTB build
> infrastructure incompatible with the way
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH is implemented. This infrastructure now
> expects all DTS files to be in vendor-specific subdirectories on the
> architectures that use this scheme. Fulfilling this kernel expectation
> would require a new configuration parameter for the name of the
> appropriate vendor subdirectory. It would also require changing the
> relative paths to included .dtsi files.
> 
> Let's add instead a rule to the top dts/Makefile for each DTB we want to
> build. This avoids breaking user's out-of-tree configurations.
> 
> [1] https://lists.buildroot.org/pipermail/buildroot/2024-October/765463.html
> 
> Reported-by: Chris Packham <judge.packham@gmail.com>
> Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>
> ---
> Changes v2 -> v3:
>   - note, in the comment and in the log message, that this issue only
>     affects some architectures
>   - expand the log message with some historical context
> These changes were suggested by Romain Naour.
> 
> Changes v1 -> v2:
>   - define a hook for LINUX_POST_PATCH_HOOKS and LINUX_POST_RSYNC_HOOKS
>     instead of modifying LINUX_BUILD_CMDS
>   - use $(patsubst %.dts,%.dtb,$(dts)) instead of $(dts:%.dts=%.dtb)
> both changes suggested by Arnout Vandecappelle.
> 
> This was build-tested with an Acqua defconfig,
> in the same manner as v2:
> 
>     # Test with an old kernel: v6.6.30
>     make acmesystems_acqua_a5_512mb_defconfig
>     make linux
> 
>     # Test with a new kernel: v6.12.8
>     make linux-dirclean
>     git am bump_Acqua_kernel_to_v6.12.8.patch
>     make acmesystems_acqua_a5_512mb_defconfig
>     make linux
> 
>     # Test the OVERRIDE_SRCDIR case.
>     make linux-dirclean
>     git -C $HOME/src/linux checkout v6.12.8
>     echo "LINUX_OVERRIDE_SRCDIR = $HOME/src/linux" > local.mk
>     make acmesystems_acqua_a5_512mb_defconfig
>     make linux
> ---
>  linux/linux.mk | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/linux/linux.mk b/linux/linux.mk
> index 12699b8ee4..e6e8a3c3bc 100644
> --- a/linux/linux.mk
> +++ b/linux/linux.mk
> @@ -327,6 +327,17 @@ define LINUX_TRY_PATCH_TIMECONST
>  endef
>  LINUX_POST_PATCH_HOOKS += LINUX_TRY_PATCH_TIMECONST
> 
> +# On some architectures, kernels 6.12+ won't compile the custom DTS
> +# files we drop into arch/$ARCH/boot/dts unless we add specific rules to
> +# that directory's Makefile.
> +define LINUX_ADD_DTB_MAKE_RULES
> +	$(foreach dts,$(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_DTS_PATH)), \
> +		echo "dtb-y += $(patsubst %.dts,%.dtb,$(notdir $(dts)))" 
>>
> $(LINUX_ARCH_PATH)/boot/dts/Makefile +	)
> +endef
> +LINUX_POST_PATCH_HOOKS += LINUX_ADD_DTB_MAKE_RULES
> +LINUX_POST_RSYNC_HOOKS += LINUX_ADD_DTB_MAKE_RULES
> +
>  LINUX_KERNEL_CUSTOM_LOGO_PATH = $(call
> qstrip,$(BR2_LINUX_KERNEL_CUSTOM_LOGO_PATH)) ifneq
> ($(LINUX_KERNEL_CUSTOM_LOGO_PATH),)
>  LINUX_DEPENDENCIES += host-imagemagick

Tested-by: Kilian Zinnecker <kilian.zinnecker@mail.de>

I applied the patch and used it in conjunction with a work in progress version 
of a board support, which had an out-of-tree dts (see discussion and patch 
below). The build worked, which indicates to me, that Edgar's patch 
successfully handled the out-of-tree dts problem introduced by the kernel 
recently.

Discussion:
https://lists.buildroot.org/pipermail/buildroot/2025-January/769859.html

Patch series:
https://lists.buildroot.org/pipermail/buildroot/2025-January/769872.html



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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Michael Walle via buildroot]

Hi,

> Fulfilling this kernel expectation would require a new
> configuration parameter for the name of the appropriate vendor
> subdirectory.

No, that doesn't work. The vendor part *has* to be included in this
config option as it may contain different device tree (file names).
Don't assume the vendor part will always be the same for different
device trees.

Somehow we have to split the source directory of the OOT device
trees and the (relative) destination within the kernel tree (eg.
'freescale/fsl-ls1028a-my-device-tree.dts', or just
'my-device-tree.dts'). Please keep in mind that the device trees
might also end up in the target filesystem in /boot and these might
also need the vendor prefix (see BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME).

> It would also require changing the relative paths to included
> .dtsi files.

Yes, but I'd argue, that the current solution is broken in this
regard. Yes we shouldn't break things, but newer OOT device trees
should use the same #include directives as the in-tree device trees
to ease sharing the files between u-boot, linux and OOT external
trees. As of today, it's not (always) possible to use the same
(OOT) device tree for u-boot and linux in buildroot, i.e. if the
arch has subdirs and one use the OF_UPSTREAM configuration option in
u-boot.

-michael
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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Romain Naour via buildroot]

Hello Edgar, Michael, All,

Le 05/01/2025 à 22:11, Michael Walle a écrit :
> Hi,
> 
>> Fulfilling this kernel expectation would require a new
>> configuration parameter for the name of the appropriate vendor
>> subdirectory.
> 
> No, that doesn't work. The vendor part *has* to be included in this
> config option as it may contain different device tree (file names).
> Don't assume the vendor part will always be the same for different
> device trees.
> 
> Somehow we have to split the source directory of the OOT device
> trees and the (relative) destination within the kernel tree (eg.
> 'freescale/fsl-ls1028a-my-device-tree.dts', or just
> 'my-device-tree.dts'). Please keep in mind that the device trees
> might also end up in the target filesystem in /boot and these might
> also need the vendor prefix (see BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME).
> 
>> It would also require changing the relative paths to included
>> .dtsi files.
> 
> Yes, but I'd argue, that the current solution is broken in this
> regard. Yes we shouldn't break things, but newer OOT device trees
> should use the same #include directives as the in-tree device trees
> to ease sharing the files between u-boot, linux and OOT external
> trees. As of today, it's not (always) possible to use the same
> (OOT) device tree for u-boot and linux in buildroot, i.e. if the
> arch has subdirs and one use the OF_UPSTREAM configuration option in
> u-boot.

Indeed, the #include directive should be the same as for the in-tree device
trees. The acmesystems_acqua_a5_* OOT dts #include path was updated to use the
vendor prefix while bumping to Linux 6.6.12 [1], so it was probably a
"workaround" of the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH limitation...

The problem is that we define the path to the OOT dts file like this:

BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/at91-sama5d3_acqua.dts"

So we can't extract the vendor prefix from it even if it would look like this:

BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/dts/microchip/at91-sama5d3_acqua.dts"

Note: the vendor prefix is not always one sub-directory:

  arch/arm/boot/dts/ti/omap/dra7.dtsi
  arch/arm64/boot/dts/exynos/google/gs101.dtsi

We probably need a new option to provide something like a dts "overlay"
BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY (similar to BR2_ROOTFS_OVERLAY) to copy a
dts directory directly to $(LINUX_ARCH_PATH)/boot/dts/

  BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY="board/acmesystems/acqua-a5/dts"

  board/acmesystems/acqua-a5/dts/
  └── microchip
      └── at91-sama5d3_acqua.dts

Doing so, the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH should be deprecated.

Thoughts?

[1]
https://gitlab.com/buildroot.org/buildroot/-/commit/8fb52098859fa5cf7ecf4db30ff8e0276687832f

Best regards,
Romain


> 
> -michael

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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Arnout Vandecappelle via buildroot]

On 22/01/2025 11:40, Romain Naour wrote:
[snip]
> The problem is that we define the path to the OOT dts file like this:
> 
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/at91-sama5d3_acqua.dts"
> 
> So we can't extract the vendor prefix from it even if it would look like this:
> 
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/dts/microchip/at91-sama5d3_acqua.dts"
> 
> Note: the vendor prefix is not always one sub-directory:
> 
>    arch/arm/boot/dts/ti/omap/dra7.dtsi
>    arch/arm64/boot/dts/exynos/google/gs101.dtsi
> 
> We probably need a new option to provide something like a dts "overlay"
> BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY (similar to BR2_ROOTFS_OVERLAY) to copy a
> dts directory directly to $(LINUX_ARCH_PATH)/boot/dts/
> 
>    BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY="board/acmesystems/acqua-a5/dts"
> 
>    board/acmesystems/acqua-a5/dts/
>    └── microchip
>        └── at91-sama5d3_acqua.dts
> 
> Doing so, the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH should be deprecated.

  Alternatively, we can define an additional config variable 
BR2_LINUX_KERNEL_CUSTOM_DTS_DIRECTORY that contains the subdirectory to which 
the custom DTS is copied. So `microchip`, `ti/omap`, or `exynos/google`.

  Disadvantage: we can't support multiple dts from different vendors. Not sure 
if that is going to be an actual use case, but people do crazy things... But I 
think for the common case (of only a single or a low number of DTSes that all 
use the same CPU (family) so are in the same directory) it works well and is 
much easier for the user.

  Regards,
  Arnout

> 
> Thoughts?
> 
> [1]
> https://gitlab.com/buildroot.org/buildroot/-/commit/8fb52098859fa5cf7ecf4db30ff8e0276687832f
> 
> Best regards,
> Romain
> 
> 
>>
>> -michael
> 

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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Romain Naour via buildroot]

Hello Arnout, All,

Le 22/01/2025 à 11:52, Arnout Vandecappelle a écrit :
> 
> 
> On 22/01/2025 11:40, Romain Naour wrote:
> [snip]
>> The problem is that we define the path to the OOT dts file like this:
>>
>> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/at91-
>> sama5d3_acqua.dts"
>>
>> So we can't extract the vendor prefix from it even if it would look like this:
>>
>> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/dts/microchip/
>> at91-sama5d3_acqua.dts"
>>
>> Note: the vendor prefix is not always one sub-directory:
>>
>>    arch/arm/boot/dts/ti/omap/dra7.dtsi
>>    arch/arm64/boot/dts/exynos/google/gs101.dtsi
>>
>> We probably need a new option to provide something like a dts "overlay"
>> BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY (similar to BR2_ROOTFS_OVERLAY) to copy a
>> dts directory directly to $(LINUX_ARCH_PATH)/boot/dts/
>>
>>    BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY="board/acmesystems/acqua-a5/dts"
>>
>>    board/acmesystems/acqua-a5/dts/
>>    └── microchip
>>        └── at91-sama5d3_acqua.dts
>>
>> Doing so, the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH should be deprecated.
> 
>  Alternatively, we can define an additional config variable
> BR2_LINUX_KERNEL_CUSTOM_DTS_DIRECTORY that contains the subdirectory to which
> the custom DTS is copied. So `microchip`, `ti/omap`, or `exynos/google`.
> 
>  Disadvantage: we can't support multiple dts from different vendors. Not sure if
> that is going to be an actual use case, but people do crazy things... But I
> think for the common case (of only a single or a low number of DTSes that all
> use the same CPU (family) so are in the same directory) it works well and is
> much easier for the user.

That was actually the Michael's comment:

"Don't assume the vendor part will always be the same for different device trees."

What if the user have to copy a file to $(LINUX_ARCH_PATH)/boot/dts/ and another
one to $(LINUX_ARCH_PATH)/boot/dts/<vendor>/ ?

It's true that it's unlikely to happen but who know?

With BR2_LINUX_KERNEL_CUSTOM_DTS_DIRECTORY solution, users can still patch their
kernels to add all missing files but it's not really nice.

Best regards,
Romain


> 
>  Regards,
>  Arnout
> 
>>
>> Thoughts?
>>
>> [1]
>> https://gitlab.com/buildroot.org/buildroot/-/
>> commit/8fb52098859fa5cf7ecf4db30ff8e0276687832f
>>
>> Best regards,
>> Romain
>>
>>
>>>
>>> -michael
>>
> 

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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Michael Walle via buildroot]

[-- Attachment #1.1: Type: text/plain, Size: 2398 bytes --]

On Wed Jan 22, 2025 at 11:52 AM CET, Arnout Vandecappelle wrote:
>
>
> On 22/01/2025 11:40, Romain Naour wrote:
> [snip]
> > The problem is that we define the path to the OOT dts file like this:
> > 
> > BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/at91-sama5d3_acqua.dts"
> > 
> > So we can't extract the vendor prefix from it even if it would look like this:
> > 
> > BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/dts/microchip/at91-sama5d3_acqua.dts"
> > 
> > Note: the vendor prefix is not always one sub-directory:
> > 
> >    arch/arm/boot/dts/ti/omap/dra7.dtsi
> >    arch/arm64/boot/dts/exynos/google/gs101.dtsi
> > 
> > We probably need a new option to provide something like a dts "overlay"
> > BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY (similar to BR2_ROOTFS_OVERLAY) to copy a
> > dts directory directly to $(LINUX_ARCH_PATH)/boot/dts/
> > 
> >    BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY="board/acmesystems/acqua-a5/dts"
> > 
> >    board/acmesystems/acqua-a5/dts/
> >    └── microchip
> >        └── at91-sama5d3_acqua.dts
> > 
> > Doing so, the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH should be deprecated.
>
>   Alternatively, we can define an additional config variable 
> BR2_LINUX_KERNEL_CUSTOM_DTS_DIRECTORY that contains the subdirectory to which 
> the custom DTS is copied. So `microchip`, `ti/omap`, or `exynos/google`.
>
>   Disadvantage: we can't support multiple dts from different vendors.

As explained earlier, I'd aim for a solution which works in any
case.

> Not sure 
> if that is going to be an actual use case, but people do crazy things... But I 
> think for the common case (of only a single or a low number of DTSes that all 
> use the same CPU (family) so are in the same directory) it works well and is 
> much easier for the user.

The kernel supports multi (sub) arch. I'd prefer it if buildroot
would support the same. Think of an OEM who wants to build common
generic image shared between all its boards.

Esp. if it would be as 'easy' as splitting the current configuration
into a config for "/path/to/dts/files" and "list/of/board.dts
or/list/of/overlay.dtso". The later could also be the same option as
used for the in-tree kernel dts list. From a POV that might even be
easier. Also, the first option (which Romain calls _OVERLAY) could
also be a list, no?

-michael

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Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Edgar Bonet]

Hello Builroot people!

On 2025-01-22, Romain Naour wrote:
> Hello Edgar, Michael, All,
> 
> Le 05/01/2025 à 22:11, Michael Walle a écrit :
>> Hi,
>>
>>> Fulfilling this kernel expectation would require a new
>>> configuration parameter for the name of the appropriate vendor
>>> subdirectory.
>>
>> No, that doesn't work. The vendor part *has* to be included in this
>> config option as it may contain different device tree (file names).
>> Don't assume the vendor part will always be the same for different
>> device trees.
>>
>> Somehow we have to split the source directory of the OOT device
>> trees and the (relative) destination within the kernel tree (eg.
>> 'freescale/fsl-ls1028a-my-device-tree.dts', or just
>> 'my-device-tree.dts'). Please keep in mind that the device trees
>> might also end up in the target filesystem in /boot and these might
>> also need the vendor prefix (see BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME).
>>
>>> It would also require changing the relative paths to included
>>> .dtsi files.
>>
>> Yes, but I'd argue, that the current solution is broken in this
>> regard. Yes we shouldn't break things, but newer OOT device trees
>> should use the same #include directives as the in-tree device trees
>> to ease sharing the files between u-boot, linux and OOT external
>> trees. As of today, it's not (always) possible to use the same
>> (OOT) device tree for u-boot and linux in buildroot, i.e. if the
>> arch has subdirs and one use the OF_UPSTREAM configuration option in
>> u-boot.
> 
> Indeed, the #include directive should be the same as for the in-tree device
> trees. The acmesystems_acqua_a5_* OOT dts #include path was updated to use the
> vendor prefix while bumping to Linux 6.6.12 [1], so it was probably a
> "workaround" of the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH limitation...
> 
> The problem is that we define the path to the OOT dts file like this:
> 
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/at91-sama5d3_acqua.dts"
> 
> So we can't extract the vendor prefix from it even if it would look like this:
> 
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/dts/microchip/at91-sama5d3_acqua.dts"
> 
> Note: the vendor prefix is not always one sub-directory:
> 
>   arch/arm/boot/dts/ti/omap/dra7.dtsi
>   arch/arm64/boot/dts/exynos/google/gs101.dtsi
> 
> We probably need a new option to provide something like a dts "overlay"
> BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY (similar to BR2_ROOTFS_OVERLAY) to copy a
> dts directory directly to $(LINUX_ARCH_PATH)/boot/dts/
> 
>   BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY="board/acmesystems/acqua-a5/dts"
> 
>   board/acmesystems/acqua-a5/dts/
>   └── microchip
>       └── at91-sama5d3_acqua.dts
> 
> Doing so, the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH should be deprecated.
> 
> Thoughts?

I do like this idea. Quite elegant. It would break current
configurations, but the fix is really easy.

I am only a bit worried about the timing. It would be nice if this issue
could be fixed, one way or another, before the feature freeze of the
next Buildroot LTS.

Best regards,

Edgar.
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