[PATCH v5.1] kernel-fit-image: allow extending compatible string property for DTBs

[PATCH v5.1] kernel-fit-image: allow extending compatible string property for DTBs

[Kavinaya S]

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_EXTENSION[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_EXTENSION[qcs6490-rb3gen2-vision-mezzanine] = "vision"
FIT_DTB_COMPATIBLE_EXTENSION[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     | 55 ++++++++++++++++++++
 4 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/meta/classes-recipe/kernel-fit-image.bbclass b/meta/classes-recipe/kernel-fit-image.bbclass
index f04aee1807..3fd31db478 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 extension if avilable
+            name, ext = os.path.splitext(dtb_name)
+            extension = (d.getVarFlag("FIT_DTB_COMPATIBLE_EXTENSION", 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_extension=extension)
 
     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..b00c1ad814 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_EXTENSION[<dtb_name>] = "<extension>"
+#
+# Result:
+#   dtb_name.dtb {
+#    ...
+#    compatible = "string1-extension", "string2", ...;
+#   };
+#
+FIT_DTB_COMPATIBLE_EXTENSION ?= ""
diff --git a/meta/lib/oe/fitimage.py b/meta/lib/oe/fitimage.py
index f303799155..58de1afaaa 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_extension=""):
         """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_extension:
+                compatible[0] = compatible[0] + "-" + compatible_extension
 
         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..582e581415 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 +822,58 @@ 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_EXTENSION[...] 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_EXTENSION[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.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_EXTENSION[{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
+        if "compatible" in its_text:
+            self.assertIn('ti,am335x-bone-green-subtypeA', its_text)
+        else:
+            pass
+
     def test_fit_image_ext_dtb_dtbo(self):
         """
         Summary:     Check if FIT image and Image Tree Source (its) are created correctly.
-- 
2.34.1

Re: [PATCH v5.1] kernel-fit-image: allow extending compatible string property for DTBs

[Dmitry Baryshkov]

On Sun, Oct 12, 2025 at 03:26:44PM +0530, Kavinaya S 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
> 

Please, don't be fancy or creative. Patch versions usually don't have
semantice versions. There is no such thing as v5.1. It's v6.

-- 
With best wishes
Dmitry

Re: [PATCH v5.1] kernel-fit-image: allow extending compatible string property for DTBs

[Kavinaya S]

On Sun, Oct 12, 2025 at 08:35 PM, Dmitry Baryshkov wrote:

>
> Please, don't be fancy or creative. Patch versions usually don't have
> semantice versions. There is no such thing as v5.1. It's v6.
> 
Sure, I will upload a new patch with v6.

> --
> With best wishes
> Dmitry
>