linux-raspberrypi: Convert dynamic config patching to config fragments

This allows us to drop all of the custom config patching in
linux-raspberrypi.inc. It also allows the kernel config to be checked
during the build for any discrepancies between the selected config
options and the resulting .config file - this identified that
`CONFIG_DRM_VC4` depends on `CONFIG_SND` and `CONFIG_SND_SOC`.

Signed-off-by: Paul Barker <pbarker@konsulko.com>

recipes-kernel/linux/files/initramfs-image-bundle.cfg

@@ -0,0 +1,3 @@
+CONFIG_OVERLAY_FS=y
+CONFIG_SQUASHFS=y
+CONFIG_UBIFS_FS=y

recipes-kernel/linux/files/vc4graphics.cfg

@@ -0,0 +1,6 @@
+CONFIG_I2C_BCM2835=y
+CONFIG_DRM=y
+CONFIG_DRM_FBDEV_EMULATION=y
+CONFIG_DRM_VC4=y
+CONFIG_SND=y
+CONFIG_SND_SOC=y

recipes-kernel/linux/linux-raspberrypi.inc

@@ -11,7 +11,11 @@ PV = "${LINUX_VERSION}+git${SRCPV}"
 inherit kernel siteinfo
 require recipes-kernel/linux/linux-yocto.inc
 
-SRC_URI += "file://rpi-kernel-misc.cfg"
+SRC_URI += " \
+    file://rpi-kernel-misc.cfg \
+    ${@bb.utils.contains("INITRAMFS_IMAGE_BUNDLE", "1", "file://initramfs-image-bundle.cfg", "", d)} \
+    ${@bb.utils.contains("MACHINE_FEATURES", "vc4graphics", "file://vc4graphics.cfg", "", d)} \
+    "
 
 KCONFIG_MODE = "--alldefconfig"
 KBUILD_DEFCONFIG_raspberrypi0-wifi ?= "bcmrpi_defconfig"
@@ -48,81 +52,6 @@ KERNEL_MODULE_AUTOLOAD += "${@bb.utils.contains("MACHINE_FEATURES", "pitft28r",
 # manually. This value unused if KERNEL_IMAGETYPE is not uImage.
 KERNEL_EXTRA_ARGS += "LOADADDR=0x00008000"
 
-# Set a variable in .configure
-# $1 - Configure variable to be set
-# $2 - value [n/y/value]
-kernel_configure_variable() {
-    # Remove the config
-    CONF_SED_SCRIPT="$CONF_SED_SCRIPT /CONFIG_$1[ =]/d;"
-    if test "$2" = "n"
-    then
-        echo "# CONFIG_$1 is not set" >> ${B}/.config
-    else
-        echo "CONFIG_$1=$2" >> ${B}/.config
-    fi
-}
-
-config_setup() {
-    # From kernel.bbclass. Unfortunately, this is needed to support builds that
-    # use devtool. The reason is as follows:
-    #
-    # - In devtool builds, externalsrc.bbclass gets inherited and sets a list of
-    # SRCTREECOVEREDTASKS, which don't get run because they affect the source
-    # tree and, when using devtool, we want the developer's changes to be the
-    # single source of truth. kernel-yocto.bbclass adds do_kernel_configme to
-    # SRCTREECOVEREDTASKS, so it doesn't run in a devtool build., In a normal
-    # non-devtool build, do_kernel_configme creates ${B}.config.
-    #
-    # - Normally (e.g. in linux-yocto), it would be OK that do_kernel_configme
-    # doesn't run, because the first few lines of do_configure in kernel.bbclass
-    # populate ${B}.config from either ${S}.config (if it exists) for custom
-    # developer changes, or otherwise from ${WORDIR}/defconfig.
-    #
-    # - In linux-raspberrypi, we add do_configure_prepend, which tweaks
-    # ${B}.config. Since this runs *before* the kernel.bbclass do_configure,
-    # ${B}.config doesn't yet exist and we hit an error. Thus we need to move
-    # the logic from do_configure up to before our do_configure_prepend. Because
-    # we are copying only a portion of do_configure and not the whole thing,
-    # there is no clean way to do it using OE functionality, so we just
-    # copy-and-paste.
-    if [ "${S}" != "${B}" ] && [ -f "${S}/.config" ] && [ ! -f "${B}/.config" ]; then
-        mv "${S}/.config" "${B}/.config"
-    fi
-
-    # Copy defconfig to .config if .config does not exist. This allows
-    # recipes to manage the .config themselves in do_configure_prepend().
-    if [ -f "${WORKDIR}/defconfig" ] && [ ! -f "${B}/.config" ]; then
-        cp "${WORKDIR}/defconfig" "${B}/.config"
-    fi
-}
-
-do_configure_prepend() {
-    config_setup
-
-    mv -f ${B}/.config ${B}/.config.patched
-    CONF_SED_SCRIPT=""
-
-    if [ "${INITRAMFS_IMAGE_BUNDLE}" = "1" ]; then
-        kernel_configure_variable OVERLAY_FS y
-        kernel_configure_variable SQUASHFS y
-        kernel_configure_variable UBIFS_FS y
-    fi
-
-    # Activate the configuration options for VC4
-    VC4GRAPHICS="${@bb.utils.contains("MACHINE_FEATURES", "vc4graphics", "1", "0", d)}"
-    if [ "${VC4GRAPHICS}" = "1" ]; then
-        kernel_configure_variable I2C_BCM2835 y
-        kernel_configure_variable DRM y
-        kernel_configure_variable DRM_FBDEV_EMULATION y
-        kernel_configure_variable DRM_VC4 y
-    fi
-
-    # Keep this the last line
-    # Remove all modified configs and add the rest to .config
-    sed -e "${CONF_SED_SCRIPT}" < '${B}/.config.patched' >> '${B}/.config'
-    rm -f ${B}/.config.patched
-}
-
 do_compile_append() {
     if [ "${SITEINFO_BITS}" = "64" ]; then
         cc_extra=$(get_cc_option)