[PATCH] linux-custom: Speedup build of target specific linux-kbuild package

[Stefan Koch <stefan-koch@siemens.com>]

Avoids time expensive QEMU-emulated merging of kernel config
by using a pregenerated kernel config for target specific linux-kbuild

Using DEPENDS instead of RDEPENDS ensures creation of
pregenerated kernel config before build of target specific linux-kbuild

Signed-off-by: Stefan Koch <stefan-koch@siemens.com>
---
 .../linux/files/debian/control.tmpl            |  8 ++++++++
 .../linux/files/debian/isar/common.tmpl        |  2 ++
 .../linux/files/debian/isar/configure.tmpl     | 18 ++++++++++++++----
 .../linux/files/debian/isar/install.tmpl       | 15 +++++++++++++++
 meta/recipes-kernel/linux/linux-custom.inc     | 14 +++++++++-----
 5 files changed, 48 insertions(+), 9 deletions(-)

diff --git a/meta/recipes-kernel/linux/files/debian/control.tmpl b/meta/recipes-kernel/linux/files/debian/control.tmpl
index e0e932a0..fa2b4e12 100644
--- a/meta/recipes-kernel/linux/files/debian/control.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/control.tmpl
@@ -50,6 +50,14 @@ Description: Linux kernel debugging symbols for @KR@
  This package will come in handy if you need to debug the kernel. It provides
  all the necessary debug symbols for the kernel and its modules.
 
+Package: linux-config-${KERNEL_NAME_PROVIDED}
+Build-Profiles: <kconfig>
+Architecture: all
+Depends: ${perl:Depends}, ${shlib:Depends}
+Description: ${KERNEL_NAME_PROVIDED} Linux kernel config for @KR@
+ This package provides the kernel config for @KR@
+ The target specific linux-kbuild package benefits from a reduced build time.
+
 Package: linux-kbuild-${KERNEL_NAME_PROVIDED}
 Build-Profiles: <kbuild !cross>
 Architecture: any
diff --git a/meta/recipes-kernel/linux/files/debian/isar/common.tmpl b/meta/recipes-kernel/linux/files/debian/isar/common.tmpl
index 86af70c5..6666c414 100644
--- a/meta/recipes-kernel/linux/files/debian/isar/common.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/isar/common.tmpl
@@ -10,6 +10,7 @@ KERNEL_PKG_IMAGE=linux-image-${KERNEL_NAME_PROVIDED}
 KERNEL_PKG_KERN_HEADERS=linux-headers-${KERNEL_NAME_PROVIDED}
 KERNEL_PKG_LIBC_HEADERS=linux-libc-dev
 KERNEL_PKG_LIBC_HEADERS_CROSS=linux-libc-dev-${DISTRO_ARCH}-cross
+KERNEL_PKG_KERN_CONFIG=linux-config-${KERNEL_NAME_PROVIDED}
 KERNEL_PKG_KERN_KBUILD=linux-kbuild-${KERNEL_NAME_PROVIDED}
 KERNEL_PKG_KERN_KBUILD_CROSS=${KERNEL_PKG_KERN_KBUILD}-${DISTRO_ARCH}-cross
 
@@ -32,6 +33,7 @@ deb_dbg_dir=${deb_img_dir}-dbg
 deb_kern_hdr_dir=${deb_top_dir}/${KERNEL_PKG_KERN_HEADERS}
 deb_libc_hdr_dir=${deb_top_dir}/${KERNEL_PKG_LIBC_HEADERS}
 deb_libc_hdr_cross_dir=${deb_top_dir}/${KERNEL_PKG_LIBC_HEADERS_CROSS}
+deb_kern_config_dir=${deb_top_dir}/${KERNEL_PKG_KERN_CONFIG}
 deb_kern_kbuild_dir=${deb_top_dir}/${KERNEL_PKG_KERN_KBUILD}
 deb_kern_kbuild_cross_dir=${deb_top_dir}/${KERNEL_PKG_KERN_KBUILD_CROSS}
 
diff --git a/meta/recipes-kernel/linux/files/debian/isar/configure.tmpl b/meta/recipes-kernel/linux/files/debian/isar/configure.tmpl
index 389c9a85..19797b84 100644
--- a/meta/recipes-kernel/linux/files/debian/isar/configure.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/isar/configure.tmpl
@@ -10,10 +10,20 @@ do_configure() {
     # Trace what we do here
     set -x
 
-    # Process kernel config target and fragments
-    ${MAKE} O=${KERNEL_BUILD_DIR} ${KERNEL_CONFIG_TARGET}
-    ./scripts/kconfig/merge_config.sh -O ${KERNEL_BUILD_DIR}/ \
-        ${KERNEL_BUILD_DIR}/.config ${KERNEL_CONFIG_FRAGMENTS}
+    configdir=/usr/lib/linux-config-${PV}
+    if [ -e ${configdir}/kernelconfig ]; then
+        # Prefer pregenerated kernel config
+        # So, very expensive QEMU-emulated merge_config.sh
+        # can be skipped for target specific linux-kbuild package
+        mkdir -p ${KERNEL_BUILD_DIR}
+        cp ${configdir}/kernelconfig ${KERNEL_BUILD_DIR}/.config
+        ${MAKE} O=${KERNEL_BUILD_DIR} olddefconfig
+    else
+        # Process kernel config target and fragments
+        ${MAKE} O=${KERNEL_BUILD_DIR} ${KERNEL_CONFIG_TARGET}
+        ./scripts/kconfig/merge_config.sh -O ${KERNEL_BUILD_DIR}/ \
+            ${KERNEL_BUILD_DIR}/.config ${KERNEL_CONFIG_FRAGMENTS}
+    fi
 
     # Stop tracing
     set +x
diff --git a/meta/recipes-kernel/linux/files/debian/isar/install.tmpl b/meta/recipes-kernel/linux/files/debian/isar/install.tmpl
index 00011517..3387671c 100644
--- a/meta/recipes-kernel/linux/files/debian/isar/install.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/isar/install.tmpl
@@ -33,6 +33,13 @@ do_install() {
     # Trace what we do here
     set -x
 
+    if echo "${DEB_BUILD_PROFILES}" | grep -q "kconfig"; then
+        # Install kernel config
+        # The target specific linux-kbuild package can speedup
+        # the build using this pregenerated kernel config
+        install_kconf ${deb_kern_config_dir}
+    fi
+
     if echo "${DEB_BUILD_PROFILES}" | grep -q "kbuild"; then
         # Install kernel scripts and tools
         if echo "${DEB_BUILD_PROFILES}" | grep -q "cross"; then
@@ -223,6 +230,14 @@ install_headers() {
     kernel_headers
 }
 
+install_kconf() {
+    kernel_kconf_dir=usr/lib/linux-config-${PV}
+    destdir=${1}/${kernel_kconf_dir}
+
+    mkdir -p ${destdir}
+    cp ${O}/${KCONF} ${destdir}/kernelconfig
+}
+
 install_kbuild() {
     kernel_kbuild_dir=usr/lib/linux-kbuild-${krel}
     destdir=${1}/${kernel_kbuild_dir}
diff --git a/meta/recipes-kernel/linux/linux-custom.inc b/meta/recipes-kernel/linux/linux-custom.inc
index 647f09dd..b21a90f3 100644
--- a/meta/recipes-kernel/linux/linux-custom.inc
+++ b/meta/recipes-kernel/linux/linux-custom.inc
@@ -25,6 +25,7 @@ KBUILD_DEPENDS ?= "build-essential:native, \
                    flex, \
                    git, \
                    kmod, \
+                   linux-config-${KERNEL_NAME_PROVIDED} <kbuild !kconfig>, \
                    rsync,"
 
 KERNEL_DEBIAN_DEPENDS ?= "initramfs-tools | linux-initramfs-tool, \
@@ -106,14 +107,14 @@ python() {
 }
 
 # Default profiles and provides
-BUILD_PROFILES = "kernel kbuild"
+BUILD_PROFILES = "kernel kconfig kbuild"
 
 # We only offer the -kbuildtarget variant when actually cross compiling
 BBCLASSEXTEND:append:cross-profile = " kbuildtarget"
 
 # When cross-profile is active:
-# build only kernel with the default variant of the recipe
-BUILD_PROFILES:cross-profile = "kernel"
+# build only kernel and package config with the default variant of the recipe
+BUILD_PROFILES:cross-profile = "kernel kconfig"
 
 # -native: kbuild package for host
 BUILD_PROFILES:class-native = "kbuild"
@@ -122,14 +123,17 @@ RECIPE_PROVIDES:class-native = " \
     linux-kbuild-${KERNEL_NAME_PROVIDED}"
 # Use pseudo target to pull in the base variant of the recipe.
 # Will be auto-extended with -native by multiarch.bbclass.
-RDEPENDS:class-native += "${BPN}-pseudo"
+# Using DEPENDS, see below
+DEPENDS:class-native += "${BPN}-pseudo"
 
 # -kbuildtarget: kbuild package for target, enforcing non-cross-build
 BUILD_PROFILES:class-kbuildtarget = "kbuild"
 RECIPE_PROVIDES:class-kbuildtarget = " \
     linux-headers-${KERNEL_NAME_PROVIDED} \
     linux-kbuild-${KERNEL_NAME_PROVIDED}"
-RDEPENDS:class-kbuildtarget = "${BPN}"
+# Using DEPENDS instead of RDEPENDS to ensure creation of pregenerated
+# kernel config before build of target specific linux-kbuild package
+DEPENDS:class-kbuildtarget = "${BPN}"
 ISAR_CROSS_COMPILE:class-kbuildtarget = "0"
 
 # Make bitbake know we will be producing linux-image and linux-headers packages
-- 
2.39.2