[PATCH 2/3] linux-custom: compile only the specified dtbs by using specific target build

["'Nicusor Huhulea' via isar-users" <isar-users@googlegroups.com>]

The current implementation makes a full kernel build and that means it will
compile all dtbs specified by the bsp makefile e.g arch/arm64/boot/dts/ti/Makefile
Currently the required dtbs are given by the DTB_FILES.

These changes are checking if the DTB_FILES is specified, compile only those
and avoids compiling all the dtbs from the bsp directory. Otherwise build all dtbs
specified by the kernel source.
Preventing the automatic dtb builds is made by using target specific build
commands e.g KERNEL_IMAGETYPE
The compilation of the dtbs accepts the following formats e.g:
Kernel Post 6.x:
a) full path from the architecture directory:
   arch/${ARCH}/boot/dts/bsp_dir/test.dts
   arch/${ARCH}/boot/dts/bsp_dir/test.dtb
b) relative path from the dts directory: bsp_dir/test.dts
c) device tree blob file: bsp_dir/test.dtb
Kernel Pre 6.x:
The same as on Kernel Post 6.x but without the bsp_dir

The differences when building a full build and when using a specific target
build are:(tests were made on the machine phyboard-mira on 6.x and 4.x versions)
specific target: Build needed 00:02:08, 2219688k disk space linux-phy 6.x
full build:      Build needed 00:02:14, 2271528k disk space linux-phy 6.x
The time difference: the full build took 6s longer than the specific target build
The disk space difference: the full build used 50.6MB more disk space than
the specific target build.
In conclusion the specific target build is slightly faster and uses less
disk space.

For now the DTB_FILES variable should accept only Device Tree Blobs(.dtb)
because some areas still depends on it e.g: do_copy_boot_files, plugins

Signed-off-by: Nicusor Huhulea <nicusor.huhulea@siemens.com>
---
 .../linux/files/debian/isar/build.tmpl        | 56 ++++++++++++++++++-
 .../linux/files/debian/isar/install.tmpl      | 12 +++-
 meta/recipes-kernel/linux/linux-custom.inc    |  6 ++
 3 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
index 1fd6f948..6f186e02 100644
--- a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
@@ -22,8 +22,13 @@ do_build() {
     sed -i "s/@KR@/${KR}/g" ${S}/debian/control ${S}/debian/linux-image-${KERNEL_NAME_PROVIDED}.*
 
     MAKE_COMMON_ARGS="O=${KERNEL_BUILD_DIR} ${PARALLEL_MAKE} KCFLAGS=${KCFLAGS} KAFLAGS=${KAFLAGS}"
-    if echo "${DEB_BUILD_PROFILES}" | grep -q "kernel"; then # Full build
-        ${MAKE} ${MAKE_COMMON_ARGS} ${KERNEL_EXTRA_BUILDARGS}
+    if echo "${DEB_BUILD_PROFILES}" | grep -q "kernel"; then
+        if [ -n "${KERNEL_IMAGETYPE}" ]; then # Override the default compilation
+            ${MAKE} ${MAKE_COMMON_ARGS} ${KERNEL_EXTRA_BUILDARGS} ${KERNEL_IMAGETYPE} modules
+            compile_dtbs
+        else $ Full build
+            ${MAKE} ${MAKE_COMMON_ARGS} ${KERNEL_EXTRA_BUILDARGS}
+        fi
     elif echo "${DEB_BUILD_PROFILES}" | grep -q "kbuild"; then # Build kernel scripts and tools
         ${MAKE} ${MAKE_COMMON_ARGS} ${KERNEL_EXTRA_BUILDARGS} scripts
         if grep -q -E "CONFIG_STACK_VALIDATION=y|CONFIG_HAVE_OBJTOOL=y" ${KERNEL_BUILD_DIR}/.config && [ -d "tools/objtool" ]; then
@@ -38,6 +43,53 @@ do_build() {
     set +x
 }
 
+compile_dtbs() {
+    local prefix="arch/${ARCH}/boot/dts/"
+
+    for dtb in ${DTB_FILES}; do
+        # Handle the case where a standalone(with no path .dtb/.dts) file may reside within
+        # a specific BSP directory or not(kernel pre-6.x)
+        if [[ ("${dtb}" == *.dtb || "${dtb}" == *.dts) && "${dtb}" != */* ]]; then
+            bsp_dir=""
+            dts_path=""
+            if [[ "${dtb}" == *.dtb ]]; then
+                dts="${dtb%.dtb}.dts"
+            else
+                dts="${dtb}"
+            fi
+
+            # recursively search for the dts file in all possible BSP directories
+            while IFS= read -r dts_path; do
+                if [ -n "${dts_path}" ]; then
+                    # Eliminate the prefix and dts to get only the bsp_dir
+                    bsp_dir="${dts_path#${prefix}}"
+                    bsp_dir="${bsp_dir%${dts}}"
+
+                    relative_dtb_path="${bsp_dir}${dtb}"
+                else
+                    relative_dtb_path="${prefix}${dtb}"
+                fi
+            done < <(find "${prefix}" -type f -name "${dts}")
+
+        # Check if the path is relative (starts with arch/${ARCH}/)
+        # and if it does then extract the relative path from the architecture specific path
+        elif [[ "${dtb}" == "${prefix}"* ]]; then
+            relative_dtb_path="${dtb#${prefix}}"
+        else
+            # directly use the given dtb
+            relative_dtb_path="${dtb}"
+        fi
+
+        # Check if it's a .dts file
+        if [[ "${relative_dtb_path}" == *.dts ]]; then
+            #  Change .dts to .dtb
+            relative_dtb_path="${relative_dtb_path%.dts}.dtb"
+        fi
+
+        ${MAKE} ${MAKE_COMMON_ARGS} ${relative_dtb_path}
+    done
+}
+
 print_settings() {
     cat <<EOF
 # Build settings:
diff --git a/meta/recipes-kernel/linux/files/debian/isar/install.tmpl b/meta/recipes-kernel/linux/files/debian/isar/install.tmpl
index 00011517..c0a60f4e 100644
--- a/meta/recipes-kernel/linux/files/debian/isar/install.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/isar/install.tmpl
@@ -124,7 +124,17 @@ install_hooks() {
 
 install_dtbs() {
     [ -n "${CONFIG_OF}" ] || return 0
-    ${MAKE} O=${O} INSTALL_DTBS_PATH=${deb_img_dir}/usr/lib/linux-image-${krel} dtbs_install
+    prefix="arch/${ARCH}/boot/dts/"
+    src_dir="${O}/${prefix}"
+    dst_dir=""
+
+    dst_dir="${deb_img_dir}/usr/lib/linux-image-${krel}/"
+    find "${src_dir}" -type f -name '*.dtb' | while IFS= read -r dtb_file; do
+        local relative_path="${dtb_file#"${src_dir}"}"
+        mkdir -p "${dst_dir}$(dirname "${relative_path}")"
+        cp "${dtb_file}" "${dst_dir}/${relative_path}"
+        echo "Copying ${dtb_file} to ${dest_dir}/${relative_path}"
+    done
 }
 
 install_kmods() {
diff --git a/meta/recipes-kernel/linux/linux-custom.inc b/meta/recipes-kernel/linux/linux-custom.inc
index 6aa70fd3..31cc480b 100644
--- a/meta/recipes-kernel/linux/linux-custom.inc
+++ b/meta/recipes-kernel/linux/linux-custom.inc
@@ -76,6 +76,7 @@ TEMPLATE_VARS += "                \
     KERNEL_DEBIAN_DEPENDS         \
     KERNEL_BUILD_DIR              \
     KERNEL_FILE                   \
+    KERNEL_IMAGETYPE              \
     KERNEL_HEADERS_DEBIAN_DEPENDS \
     LINUX_VERSION_EXTENSION       \
     KERNEL_NAME_PROVIDED          \
@@ -84,12 +85,17 @@ TEMPLATE_VARS += "                \
     KAFLAGS                       \
     DISTRIBUTOR                   \
     KERNEL_EXTRA_BUILDARGS        \
+    DTB_FILES                     \
 "
 
 inherit dpkg
 inherit template
 inherit kbuildtarget
 
+DTB_FILES ?= ""
+
+KERNEL_IMAGETYPE ?= ""
+
 # Add custom cflags to the kernel build
 KCFLAGS ?= "-fdebug-prefix-map=${CURDIR}=."
 KAFLAGS ?= "-fdebug-prefix-map=${CURDIR}=."
-- 
2.39.2

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