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

Alexander Kanavin
2025-10-11T17:33:04Z

Just wanted to say this looks fine to me on a (very) quick read, so if
Dmitry and people on the patch review call have no objections, neither
do I. It needs to pass the autobuilder testing too, you will hear if
something goes wrong.

Alex

On Sat, 11 Oct 2025 at 11:48, Kavinaya S <kavinaya@qti.qualcomm.com> 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"
>
> 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.