build-dtb-image: probe Debian standard DTB path first in --kernel-deb mode

When extracting DTBs from a kernel .deb, probe paths in order:
  1. usr/lib/linux-image-*/        (Debian standard — direct, no symlink)
  2. usr/lib/firmware/*/device-tree (Ubuntu compat, usrmerge layout)
  3. lib/firmware/*/device-tree     (Ubuntu compat, legacy layout)

Probing the Debian standard path first avoids any dependency on the
Ubuntu compat symlink and works correctly on pure Debian systems that
never install it, as well as on Ubuntu regardless of usrmerge layout.

The fallback chain is fully backward compatible: legacy packages
(built by build-kernel-deb.sh) only populate lib/firmware/, so the
script falls through steps 1 and 2 and resolves via step 3 as before.

Signed-off-by: Bjordis Collaku <bcollaku@qti.qualcomm.com>

Author: bjordiscollaku

kernel/scripts/build-dtb-image.sh

@@ -18,12 +18,13 @@
 #     (A) Kernel .deb mode (recommended / upstream-friendly)
 #         - Provide a Debian kernel package (.deb) as input.
 #         - The script extracts the .deb via `dpkg-deb -R` into a temp directory.
-#         - DTBs are expected to be present under:
-#             $DEB_DIR/usr/lib/firmware/$BASE_KERNEL_VERSION/device-tree  (usrmerge layout)
-#             $DEB_DIR/lib/firmware/$BASE_KERNEL_VERSION/device-tree       (legacy layout)
-#           where $BASE_KERNEL_VERSION can be anything.
-#         - The script assumes there is exactly ONE device-tree directory across
-#           both search paths.
+#         - DTBs are located by probing the following paths in order:
+#             1. $DEB_DIR/usr/lib/linux-image-*/   (Debian standard — direct, no symlink)
+#             2. $DEB_DIR/usr/lib/firmware/*/device-tree  (Ubuntu compat, usrmerge layout)
+#             3. $DEB_DIR/lib/firmware/*/device-tree      (Ubuntu compat, legacy layout)
+#           Probing the Debian standard path first ensures correct operation on
+#           both Debian and Ubuntu regardless of whether the compat symlink exists.
+#         - The script assumes there is exactly ONE matching directory.
 #
 #     (B) DTB source directory mode (dev/kernel-tree mode)
 #         - Provide the DTB source directory directly (e.g. a kernel build tree):
@@ -171,10 +172,11 @@ usage() {
     cat <<EOF
 Usage: $0 (--kernel-deb <kernel.deb> | --dtb-src <path>) --manifest <file> [--size <MB>] [--out <file>]
 
-  --kernel-deb, -kernel-deb  Path to Debian kernel package (.deb). DTBs read from:
-                             <extract>/usr/lib/firmware/*/device-tree  (usrmerge layout)
-                             <extract>/lib/firmware/*/device-tree       (legacy layout)
-                             Exactly one device-tree directory must be found.
+  --kernel-deb, -kernel-deb  Path to Debian kernel package (.deb). DTBs located by probing:
+                             1. <extract>/usr/lib/linux-image-*/        (Debian standard)
+                             2. <extract>/usr/lib/firmware/*/device-tree (Ubuntu, usrmerge)
+                             3. <extract>/lib/firmware/*/device-tree     (Ubuntu, legacy)
+                             Exactly one directory must be found across all search paths.
 
   --dtb-src,   -dtb-src      Path to DTB source directory
                              (e.g. arch/arm64/boot/dts/qcom)
@@ -364,19 +366,27 @@ if [[ -n "${KERNEL_DEB}" ]]; then
     echo "[INFO] Extracting kernel .deb to: ${DEB_DIR}"
     dpkg-deb -R "${KERNEL_DEB}" "${DEB_DIR}"
 
-    # Locate exactly one device-tree directory.
-    # Modern packages (usrmerge / pkg-linux-qcom) install the compat symlink under
-    # usr/lib/firmware/<KVER>/device-tree; legacy packages used lib/firmware/.
-    # Check usr/lib/firmware/ first; fall back to lib/firmware/.
+    # Locate the DTB directory from the extracted .deb.
+    # Probe in order (most to least preferred):
+    #   1. usr/lib/linux-image-*/  — Debian standard install location (direct, no symlink).
+    #                                Works on both Debian and Ubuntu regardless of usrmerge.
+    #   2. usr/lib/firmware/*/device-tree — Ubuntu compat symlink (usrmerge layout).
+    #   3. lib/firmware/*/device-tree     — Ubuntu compat symlink (legacy layout).
+    # Searching the Debian standard path first avoids any dependency on the Ubuntu
+    # compat symlink and is correct on pure Debian systems that never install it.
     shopt -s nullglob
-    dt_dirs=( "${DEB_DIR}/usr/lib/firmware"/*/device-tree )
+    dt_dirs=( "${DEB_DIR}/usr/lib/linux-image-"*/ )
+    if (( ${#dt_dirs[@]} == 0 )); then
+        dt_dirs=( "${DEB_DIR}/usr/lib/firmware"/*/device-tree )
+    fi
     if (( ${#dt_dirs[@]} == 0 )); then
         dt_dirs=( "${DEB_DIR}/lib/firmware"/*/device-tree )
     fi
     shopt -u nullglob
 
     if (( ${#dt_dirs[@]} == 0 )); then
         echo "[ERROR] No DTB directory found under:" >&2
+        echo "        '${DEB_DIR}/usr/lib/linux-image-*/'" >&2
         echo "        '${DEB_DIR}/usr/lib/firmware/*/device-tree'" >&2
         echo "        '${DEB_DIR}/lib/firmware/*/device-tree'" >&2
         exit 1
@@ -530,7 +540,7 @@ else
     if (( dtb_count == 0 )); then
         echo "[ERROR] No DTB files found under ${DTB_SRC}" >&2
         echo "        Verify the kernel package was built with DTB support" >&2
-        echo "        and that usr/lib/firmware/*/device-tree resolves correctly." >&2
+        echo "        and that usr/lib/linux-image-*/ is present in the package." >&2
         exit 1
     fi
     echo "[INFO] Staged ${dtb_count} DTB file(s) to ${DTB_STAGE}"