Re: [OE-core] [PATCH v5] kernel-fit-image: allow extending compatible string property for DTBs

[Gyorgy Sarvari <skandigraun@gmail.com>]

On 10/11/25 11:48, Kavinaya S via lists.openembedded.org wrote:
> The Linux kernel allows multiple DTBs to share the same compatible string.
> For example:
> qcs6490-rb3gen2.dtb
> qcs6490-rb3gen2-vision-mezzanine.dtb
> qcs6490-rb3gen2-industrial-mezzanine.dtb
>
> All of these use the same base compatible string:
> compatible = "qcom,qcs6490-rb3gen2", "qcom,qcm6490";
>
> Since the latter two DTBs are overlays on top of the base DTB and do not
> modify platform properties, they retain the same compatible string.
>
> When these DTBs are bundled into a single fitImage, the bootloader cannot
> distinguish between them due to identical compatible strings.
>
> To address this, introduce a mechanism to extend the compatible string
> using a OE build variable:
> FIT_DTB_COMPATIBLE_EXTENTION[dtb_name] = "extension"

One small note: "extension" is misspelled as "extention" multiple times
in the patch.

> This appends the extension to the first compatible string in the DTB,
> resulting in unique entries in the generated .its file. For example:
> FIT_DTB_COMPATIBLE_EXTENTION[qcs6490-rb3gen2-vision-mezzanine] = "vision"
> FIT_DTB_COMPATIBLE_EXTENTION[qcs6490-rb3gen2-industrial-mezzanine] = "industrial"
>
> Generates:
> compatible = "qcom,qcs6490-rb3gen2-vision", "qcom,qcm6490";
> compatible = "qcom,qcs6490-rb3gen2-industrial", "qcom,qcm6490";
>
> Suggested-By: Alexander Kanavin <alex.kanavin@gmail.com>
> Suggested-By: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> Signed-off-by: Kavinaya S <kavinaya@qti.qualcomm.com>
> ---
>  meta/classes-recipe/kernel-fit-image.bbclass |  8 ++-
>  meta/conf/image-fitimage.conf                | 12 +++++
>  meta/lib/oe/fitimage.py                      |  4 +-
>  meta/lib/oeqa/selftest/cases/fitimage.py     | 52 ++++++++++++++++++++
>  4 files changed, 74 insertions(+), 2 deletions(-)
>
> diff --git a/meta/classes-recipe/kernel-fit-image.bbclass b/meta/classes-recipe/kernel-fit-image.bbclass
> index f04aee1807..7850d565fc 100644
> --- a/meta/classes-recipe/kernel-fit-image.bbclass
> +++ b/meta/classes-recipe/kernel-fit-image.bbclass
> @@ -84,8 +84,14 @@ python do_compile() {
>  
>              # Copy the dtb or dtbo file into the FIT image assembly directory
>              shutil.copyfile(os.path.join(kernel_deploydir, dtb_name), dtb_name)
> +
> +            # Consider compatible extention if avilable
> +            name, ext = os.path.splitext(dtb_name)
> +            extention = (d.getVarFlag("FIT_DTB_COMPATIBLE_EXTENTION", name) or "").strip()
> +
>              root_node.fitimage_emit_section_dtb(dtb_name, dtb_name,
> -                d.getVar("UBOOT_DTB_LOADADDRESS"), d.getVar("UBOOT_DTBO_LOADADDRESS"))
> +                d.getVar("UBOOT_DTB_LOADADDRESS"), d.getVar("UBOOT_DTBO_LOADADDRESS"),
> +                compatible_extention=extention)
>  
>      if external_kernel_devicetree:
>          # iterate over all .dtb and .dtbo files in the external kernel devicetree directory
> diff --git a/meta/conf/image-fitimage.conf b/meta/conf/image-fitimage.conf
> index 090ee148f4..86948b6bf3 100644
> --- a/meta/conf/image-fitimage.conf
> +++ b/meta/conf/image-fitimage.conf
> @@ -65,3 +65,15 @@ FIT_ADDRESS_CELLS ?= "1"
>  # Machine configurations needing such a script file should include it in the
>  # SRC_URI of the kernel recipe and set the FIT_UBOOT_ENV parameter.
>  FIT_UBOOT_ENV ?= ""
> +
> +# For specific DTBs extend "compatible" strings when creating FIT images.
> +# Format:
> +#   FIT_DTB_COMPATIBLE_EXTENTION[<dtb_name>] = "<extension>"
> +#
> +# Result:
> +#   dtb_name.dtb {
> +#    ...
> +#    compatible = "string1-extension", "string2", ...;
> +#   };
> +#
> +FIT_DTB_COMPATIBLE_EXTENTION ?= ""
> diff --git a/meta/lib/oe/fitimage.py b/meta/lib/oe/fitimage.py
> index f303799155..98af4aad14 100644
> --- a/meta/lib/oe/fitimage.py
> +++ b/meta/lib/oe/fitimage.py
> @@ -289,7 +289,7 @@ class ItsNodeRootKernel(ItsNode):
>          self._kernel = kernel_node
>  
>      def fitimage_emit_section_dtb(self, dtb_id, dtb_path, dtb_loadaddress=None,
> -                                  dtbo_loadaddress=None, add_compatible=False):
> +                                  dtbo_loadaddress=None, add_compatible=False, compatible_extention=""):
>          """Emit the fitImage ITS DTB section"""
>          load=None
>          dtb_ext = os.path.splitext(dtb_path)[1]
> @@ -310,6 +310,8 @@ class ItsNodeRootKernel(ItsNode):
>          compatible = None
>          if add_compatible:
>              compatible = get_compatible_from_dtb(dtb_path)
> +            if compatible and compatible_extention:
> +                compatible[0] = compatible[0] + "-" + compatible_extention
>  
>          dtb_node = self.its_add_node_dtb(
>              "fdt-" + dtb_id,
> diff --git a/meta/lib/oeqa/selftest/cases/fitimage.py b/meta/lib/oeqa/selftest/cases/fitimage.py
> index 195b9ee8b5..dfe34ccdec 100644
> --- a/meta/lib/oeqa/selftest/cases/fitimage.py
> +++ b/meta/lib/oeqa/selftest/cases/fitimage.py
> @@ -17,6 +17,9 @@ from oeqa.selftest.case import OESelftestTestCase
>  from oeqa.utils.commands import runCmd, bitbake, get_bb_vars, get_bb_var
>  
>  
> +from pathlib import Path
> +
> +
>  class BbVarsMockGenKeys:
>      def __init__(self, keydir, gen_keys="0", sign_enabled="0", keyname="", sign_ind="0", img_keyname=""):
>          self.bb_vars = {
> @@ -819,6 +822,55 @@ MACHINE:forcevariable = "beaglebone-yocto"
>          # The alias is a symlink, therefore the compatible string is equal
>          self.assertEqual(comp_alias, comp)
>  
> +    def test_fitimage_compatible_extn_in_its(self):
> +        """
> +        Verify that FIT_DTB_COMPATIBLE_EXTENTION[...] is honored in the generated .its.
> +
> +        This test:
> +        1) Selects beaglebone-yocto machine and a DTB that is part of its kernel.
> +        2) Sets FIT_DTB_COMPATIBLE_EXTENTION[am335x-bonegreen-ext] to custom extension.
> +        3) Runs do_assemble_fitimage to generate the FIT .its.
> +        4) Asserts the .its 'compatible = ...' includes extended ones.
> +
> +        """
> +
> +        kernel_dtb = "am335x-bonegreen-ext.dtb"
> +        dtb_name = os.path.splitext(os.path.basename(kernel_dtb))[0]
> +
> +        config = f"""
> +DISTRO = "poky"
> +MACHINE = "beaglebone-yocto"
> +
> +# Ensure the FIT flow is active
> +KERNEL_CLASSES += "kernel-fit-extra-artifacts "
> +
> +# Ensure the selected DTB is built into the kernel deploy output
> +KERNEL_DEVICETREE = "{kernel_dtb}"
> +
> +# Provide the extension as a varflag (pairs: base:suffix)
> +# Original compatibles: "ti,am335x-bone-green", "ti,am335x-bone-black"
> +FIT_DTB_COMPATIBLE_EXTENTION[{dtb_name}] = "subtypeA"
> +
> +"""
> +        self.write_config(config)
> +
> +        bitbake('virtual/kernel:do_deploy')
> +        bitbake('linux-yocto-fitimage:do_deploy')
> +
> +        # Find the generated .its in DEPLOY_DIR_IMAGE
> +        deploy_dir_image = get_bb_var('DEPLOY_DIR_IMAGE')
> +        self.assertTrue(deploy_dir_image and os.path.isdir(deploy_dir_image),
> +                    f"DEPLOY_DIR_IMAGE not found or invalid: {deploy_dir_image}")
> +
> +        its_path = os.path.join(deploy_dir_image, 'fit-image.its')
> +        self.assertTrue(os.path.exists(its_path), f"Expected ITS file not found: {its_path}")
> +
> +        # Read the ITS content
> +        its_text = Path(its_path).read_text(encoding='utf-8', errors='ignore')
> +
> +        # Assertions: extended compatibles must appear
> +        self.assertIn('ti,am335x-bone-green-subtypeA', its_text)
> +
>      def test_fit_image_ext_dtb_dtbo(self):
>          """
>          Summary:     Check if FIT image and Image Tree Source (its) are created correctly.
>
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