kbuild: allow architectures to specify defconfig file with KBUILD_DEFCONFIG

For some architectures is does not make sense to maintain a single default
configuration - arm is a good example here.
KBUILD_DEFCONFIG is introduced allowing relevant architectures to point out
a configuration kept in arch/$(ARCH)/configs as the configuration
to be used when executing 'make defconfig'.
This patch selects versatile_defconfig as the default configuration for arm.

The reason to keep defconfig is that is has proved valuable in many testing
scenarios when one are doing a cross architecture build of the kernel to
do a simple compile-time check of some changes.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -440,6 +440,12 @@ ifeq ($(config-targets),1)
 # *config targets only - make sure prerequisites are updated, and descend
 # in scripts/kconfig to make the *config target
 
+# Read arch specific Makefile to set KBUILD_DEFCONFIG as needed.
+# KBUILD_DEFCONFIG may point out an alternative default configuration
+# used for 'make defconfig'
+include $(srctree)/arch/$(ARCH)/Makefile
+export KBUILD_DEFCONFIG
+
 config: scripts_basic outputmakefile FORCE
 	$(Q)$(MAKE) $(build)=scripts/kconfig $@
 %config: scripts_basic outputmakefile FORCE

arch/arm/Makefile

@@ -13,6 +13,10 @@ OBJCOPYFLAGS	:=-O binary -R .note -R .comment -S
 GZFLAGS		:=-9
 #CFLAGS		+=-pipe
 
+# Do not use arch/arm/defconfig - it's always outdated.
+# Select a platform tht is kept up-to-date
+KBUILD_DEFCONFIG := versatile_defconfig
+
 ifeq ($(CONFIG_FRAME_POINTER),y)
 CFLAGS		+=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
 endif

arch/arm/defconfig

-#
-# Automatically generated make config: don't edit
-#
-CONFIG_ARM=y
-# CONFIG_EISA is not set
-# CONFIG_SBUS is not set
-# CONFIG_MCA is not set
-CONFIG_UID16=y
-
-#
-# Code maturity level options
-#
-CONFIG_EXPERIMENTAL=y
-# CONFIG_OBSOLETE is not set
-
-#
-# Loadable module support
-#
-# CONFIG_MODULES is not set
-
-#
-# System Type
-#
-# CONFIG_ARCH_ARCA5K is not set
-# CONFIG_ARCH_CLPS7500 is not set
-# CONFIG_ARCH_CO285 is not set
-# CONFIG_ARCH_EBSA110 is not set
-# CONFIG_ARCH_FOOTBRIDGE is not set
-CONFIG_ARCH_INTEGRATOR=y
-# CONFIG_ARCH_RPC is not set
-# CONFIG_ARCH_SA1100 is not set
-# CONFIG_ARCH_CLPS711X is not set
-
-#
-# Archimedes/A5000 Implementations
-#
-
-#
-# Footbridge Implementations
-#
-
-#
-# SA11x0 Implementations
-#
-
-#
-# CLPS711X/EP721X Implementations
-#
-# CONFIG_ARCH_ACORN is not set
-# CONFIG_FOOTBRIDGE is not set
-# CONFIG_FOOTBRIDGE_HOST is not set
-# CONFIG_FOOTBRIDGE_ADDIN is not set
-CONFIG_CPU_32=y
-# CONFIG_CPU_26 is not set
-
-#
-# Processor Type
-#
-CONFIG_CPU_32v4=y
-CONFIG_CPU_ARM720=y
-CONFIG_CPU_ARM920=y
-CONFIG_CPU_ARM920_CPU_IDLE=y
-CONFIG_CPU_ARM920_I_CACHE_ON=y
-CONFIG_CPU_ARM920_D_CACHE_ON=y
-# CONFIG_CPU_ARM920_WRITETHROUGH is not set
-# CONFIG_DISCONTIGMEM is not set
-
-#
-# General setup
-#
-# CONFIG_ANGELBOOT is not set
-CONFIG_PCI_INTEGRATOR=y
-CONFIG_PCI=y
-# CONFIG_ISA is not set
-# CONFIG_ISA_DMA is not set
-CONFIG_PCI_NAMES=y
-# CONFIG_HOTPLUG is not set
-# CONFIG_PCMCIA is not set
-CONFIG_NET=y
-CONFIG_SYSVIPC=y
-# CONFIG_BSD_PROCESS_ACCT is not set
-CONFIG_SYSCTL=y
-CONFIG_NWFPE=y
-CONFIG_KCORE_ELF=y
-# CONFIG_KCORE_AOUT is not set
-CONFIG_BINFMT_AOUT=y
-CONFIG_BINFMT_ELF=y
-# CONFIG_BINFMT_MISC is not set
-# CONFIG_PM is not set
-# CONFIG_ARTHUR is not set
-CONFIG_CMDLINE="root=1f04 mem=32M"
-CONFIG_LEDS=y
-CONFIG_LEDS_TIMER=y
-CONFIG_LEDS_CPU=y
-CONFIG_ALIGNMENT_TRAP=y
-
-#
-# Parallel port support
-#
-# CONFIG_PARPORT is not set
-
-#
-# Memory Technology Devices (MTD)
-#
-CONFIG_MTD=y
-# CONFIG_MTD_DOC1000 is not set
-# CONFIG_MTD_DOC2000 is not set
-# CONFIG_MTD_DOC2001 is not set
-# CONFIG_MTD_DOCPROBE is not set
-# CONFIG_MTD_SLRAM is not set
-# CONFIG_MTD_PMC551 is not set
-# CONFIG_MTD_MTDRAM is not set
-
-#
-# MTD drivers for mapped chips
-#
-CONFIG_MTD_CFI=y
-CONFIG_MTD_CFI_INTELEXT=y
-# CONFIG_MTD_CFI_AMDSTD is not set
-# CONFIG_MTD_JEDEC is not set
-# CONFIG_MTD_RAM is not set
-# CONFIG_MTD_ROM is not set
-# CONFIG_MTD_PHYSMAP is not set
-
-#
-# Drivers for chip mappings
-#
-# CONFIG_MTD_MIXMEM is not set
-# CONFIG_MTD_NORA is not set
-# CONFIG_MTD_OCTAGON is not set
-# CONFIG_MTD_PNC2000 is not set
-# CONFIG_MTD_RPXLITE is not set
-# CONFIG_MTD_VMAX is not set
-
-#
-# User modules and translation layers for MTD devices
-#
-CONFIG_MTD_CHAR=y
-CONFIG_MTD_BLOCK=y
-# CONFIG_FTL is not set
-# CONFIG_NFTL is not set
-CONFIG_MTD_ARM=y
-
-#
-# Plug and Play configuration
-#
-# CONFIG_PNP is not set
-# CONFIG_ISAPNP is not set
-
-#
-# Block devices
-#
-# CONFIG_BLK_DEV_FD is not set
-# CONFIG_BLK_DEV_XD is not set
-# CONFIG_PARIDE is not set
-# CONFIG_BLK_CPQ_DA is not set
-# CONFIG_BLK_CPQ_CISS_DA is not set
-# CONFIG_BLK_DEV_DAC960 is not set
-# CONFIG_BLK_DEV_LOOP is not set
-# CONFIG_BLK_DEV_NBD is not set
-CONFIG_BLK_DEV_RAM=y
-CONFIG_BLK_DEV_RAM_SIZE=4096
-# CONFIG_BLK_DEV_INITRD is not set
-
-#
-# Networking options
-#
-# CONFIG_PACKET is not set
-# CONFIG_NETLINK is not set
-# CONFIG_NETFILTER is not set
-# CONFIG_FILTER is not set
-CONFIG_UNIX=y
-CONFIG_INET=y
-# CONFIG_IP_MULTICAST is not set
-# CONFIG_IP_ADVANCED_ROUTER is not set
-CONFIG_IP_PNP=y
-CONFIG_IP_PNP_BOOTP=y
-# CONFIG_IP_PNP_RARP is not set
-# CONFIG_NET_IPIP is not set
-# CONFIG_NET_IPGRE is not set
-# CONFIG_INET_ECN is not set
-# CONFIG_SYN_COOKIES is not set
-# CONFIG_IPV6 is not set
-# CONFIG_KHTTPD is not set
-# CONFIG_ATM is not set
-
-#
-#  
-#
-# CONFIG_IPX is not set
-# CONFIG_ATALK is not set
-# CONFIG_DECNET is not set
-# CONFIG_BRIDGE is not set
-# CONFIG_X25 is not set
-# CONFIG_LAPB is not set
-# CONFIG_LLC is not set
-# CONFIG_NET_DIVERT is not set
-# CONFIG_ECONET is not set
-# CONFIG_WAN_ROUTER is not set
-# CONFIG_NET_HW_FLOWCONTROL is not set
-
-#
-# QoS and/or fair queueing
-#
-# CONFIG_NET_SCHED is not set
-
-#
-# Network device support
-#
-CONFIG_NETDEVICES=y
-
-#
-# ARCnet devices
-#
-# CONFIG_ARCNET is not set
-# CONFIG_DUMMY is not set
-# CONFIG_BONDING is not set
-# CONFIG_EQUALIZER is not set
-# CONFIG_TUN is not set
-# CONFIG_NET_SB1000 is not set
-
-#
-# Ethernet (10 or 100Mbit)
-#
-CONFIG_NET_ETHERNET=y
-# CONFIG_NET_VENDOR_3COM is not set
-# CONFIG_LANCE is not set
-# CONFIG_NET_VENDOR_SMC is not set
-# CONFIG_NET_VENDOR_RACAL is not set
-# CONFIG_AT1700 is not set
-# CONFIG_DEPCA is not set
-# CONFIG_HP100 is not set
-# CONFIG_NET_ISA is not set
-CONFIG_NET_PCI=y
-# CONFIG_PCNET32 is not set
-# CONFIG_ADAPTEC_STARFIRE is not set
-# CONFIG_APRICOT is not set
-# CONFIG_CS89x0 is not set
-CONFIG_TULIP=y
-# CONFIG_DE4X5 is not set
-# CONFIG_DGRS is not set
-# CONFIG_DM9102 is not set
-CONFIG_EEPRO100=y
-CONFIG_EEPRO100_PM=y
-# CONFIG_LNE390 is not set
-# CONFIG_NATSEMI is not set
-# CONFIG_NE2K_PCI is not set
-# CONFIG_NE3210 is not set
-# CONFIG_ES3210 is not set
-# CONFIG_8139TOO is not set
-# CONFIG_RTL8129 is not set
-# CONFIG_SIS900 is not set
-# CONFIG_EPIC100 is not set
-# CONFIG_SUNDANCE is not set
-# CONFIG_TLAN is not set
-# CONFIG_VIA_RHINE is not set
-# CONFIG_WINBOND_840 is not set
-# CONFIG_HAPPYMEAL is not set
-# CONFIG_NET_POCKET is not set
-
-#
-# Ethernet (1000 Mbit)
-#
-# CONFIG_ACENIC is not set
-# CONFIG_HAMACHI is not set
-# CONFIG_YELLOWFIN is not set
-# CONFIG_SK98LIN is not set
-# CONFIG_FDDI is not set
-# CONFIG_HIPPI is not set
-# CONFIG_PPP is not set
-# CONFIG_SLIP is not set
-
-#
-# Wireless LAN (non-hamradio)
-#
-# CONFIG_NET_RADIO is not set
-
-#
-# Token Ring devices
-#
-# CONFIG_TR is not set
-# CONFIG_NET_FC is not set
-# CONFIG_RCPCI is not set
-# CONFIG_SHAPER is not set
-
-#
-# Wan interfaces
-#
-# CONFIG_WAN is not set
-
-#
-# Amateur Radio support
-#
-# CONFIG_HAMRADIO is not set
-
-#
-# IrDA (infrared) support
-#
-# CONFIG_IRDA is not set
-
-#
-# ATA/IDE/MFM/RLL support
-#
-# CONFIG_IDE is not set
-# CONFIG_BLK_DEV_HD is not set
-
-#
-# SCSI support
-#
-# CONFIG_SCSI is not set
-
-#
-# IEEE 1394 (FireWire) support
-#
-# CONFIG_IEEE1394 is not set
-
-#
-# I2O device support
-#
-# CONFIG_I2O is not set
-# CONFIG_I2O_PCI is not set
-# CONFIG_I2O_BLOCK is not set
-# CONFIG_I2O_LAN is not set
-# CONFIG_I2O_SCSI is not set
-# CONFIG_I2O_PROC is not set
-
-#
-# ISDN subsystem
-#
-# CONFIG_ISDN is not set
-
-#
-# Input core support
-#
-# CONFIG_INPUT is not set
-
-#
-# Character devices
-#
-CONFIG_VT=y
-CONFIG_VT_CONSOLE=y
-# CONFIG_SERIAL is not set
-# CONFIG_SERIAL_EXTENDED is not set
-# CONFIG_SERIAL_NONSTANDARD is not set
-CONFIG_SERIAL_AMBA=y
-CONFIG_SERIAL_INTEGRATOR=y
-CONFIG_SERIAL_AMBA_CONSOLE=y
-CONFIG_UNIX98_PTYS=y
-CONFIG_UNIX98_PTY_COUNT=256
-
-#
-# I2C support
-#
-# CONFIG_I2C is not set
-
-#
-# Mice
-#
-# CONFIG_BUSMOUSE is not set
-CONFIG_MOUSE=y
-CONFIG_PSMOUSE=y
-# CONFIG_82C710_MOUSE is not set
-# CONFIG_PC110_PAD is not set
-
-#
-# Joysticks
-#
-# CONFIG_JOYSTICK is not set
-
-#
-# Input core support is needed for joysticks
-#
-# CONFIG_QIC02_TAPE is not set
-
-#
-# Watchdog Cards
-#
-# CONFIG_WATCHDOG is not set
-# CONFIG_INTEL_RNG is not set
-# CONFIG_NVRAM is not set
-# CONFIG_RTC is not set
-# CONFIG_DTLK is not set
-# CONFIG_R3964 is not set
-# CONFIG_APPLICOM is not set
-
-#
-# Ftape, the floppy tape device driver
-#
-# CONFIG_FTAPE is not set
-# CONFIG_AGP is not set
-# CONFIG_DRM is not set
-
-#
-# Multimedia devices
-#
-# CONFIG_VIDEO_DEV is not set
-
-#
-# File systems
-#
-# CONFIG_QUOTA is not set
-# CONFIG_AUTOFS_FS is not set
-# CONFIG_AUTOFS4_FS is not set
-# CONFIG_ADFS_FS is not set
-# CONFIG_ADFS_FS_RW is not set
-# CONFIG_AFFS_FS is not set
-# CONFIG_HFS_FS is not set
-# CONFIG_BFS_FS is not set
-# CONFIG_FAT_FS is not set
-# CONFIG_MSDOS_FS is not set
-# CONFIG_UMSDOS_FS is not set
-# CONFIG_VFAT_FS is not set
-# CONFIG_EFS_FS is not set
-# CONFIG_JFFS_FS is not set
-# CONFIG_CRAMFS is not set
-# CONFIG_RAMFS is not set
-# CONFIG_ISO9660_FS is not set
-# CONFIG_JOLIET is not set
-# CONFIG_MINIX_FS is not set
-# CONFIG_NTFS_FS is not set
-# CONFIG_NTFS_DEBUG is not set
-# CONFIG_NTFS_RW is not set
-# CONFIG_HPFS_FS is not set
-CONFIG_PROC_FS=y
-# CONFIG_DEVFS_FS is not set
-# CONFIG_DEVFS_MOUNT is not set
-# CONFIG_DEVFS_DEBUG is not set
-CONFIG_DEVPTS_FS=y
-# CONFIG_QNX4FS_FS is not set
-# CONFIG_QNX4FS_RW is not set
-CONFIG_ROMFS_FS=y
-CONFIG_EXT2_FS=y
-# CONFIG_SYSV_FS is not set
-# CONFIG_SYSV_FS_WRITE is not set
-# CONFIG_UDF_FS is not set
-# CONFIG_UDF_RW is not set
-# CONFIG_UFS_FS is not set
-# CONFIG_UFS_FS_WRITE is not set
-
-#
-# Network File Systems
-#
-# CONFIG_CODA_FS is not set
-CONFIG_NFS_FS=y
-# CONFIG_NFS_V3 is not set
-CONFIG_ROOT_NFS=y
-# CONFIG_NFSD is not set
-# CONFIG_NFSD_V3 is not set
-CONFIG_SUNRPC=y
-CONFIG_LOCKD=y
-# CONFIG_SMB_FS is not set
-# CONFIG_NCP_FS is not set
-# CONFIG_NCPFS_PACKET_SIGNING is not set
-# CONFIG_NCPFS_IOCTL_LOCKING is not set
-# CONFIG_NCPFS_STRONG is not set
-# CONFIG_NCPFS_NFS_NS is not set
-# CONFIG_NCPFS_OS2_NS is not set
-# CONFIG_NCPFS_SMALLDOS is not set
-# CONFIG_NCPFS_MOUNT_SUBDIR is not set
-# CONFIG_NCPFS_NDS_DOMAINS is not set
-# CONFIG_NCPFS_NLS is not set
-# CONFIG_NCPFS_EXTRAS is not set
-
-#
-# Partition Types
-#
-CONFIG_PARTITION_ADVANCED=y
-# CONFIG_ACORN_PARTITION is not set
-# CONFIG_OSF_PARTITION is not set
-# CONFIG_AMIGA_PARTITION is not set
-# CONFIG_ATARI_PARTITION is not set
-# CONFIG_MAC_PARTITION is not set
-# CONFIG_MSDOS_PARTITION is not set
-# CONFIG_SGI_PARTITION is not set
-# CONFIG_ULTRIX_PARTITION is not set
-# CONFIG_SUN_PARTITION is not set
-# CONFIG_NLS is not set
-
-#
-# Console drivers
-#
-CONFIG_KMI_KEYB=y
-CONFIG_PC_KEYMAP=y
-CONFIG_VGA_CONSOLE=y
-# CONFIG_FB is not set
-
-#
-# Frame-buffer support
-#
-# CONFIG_FB is not set
-
-#
-# Sound
-#
-# CONFIG_SOUND is not set
-
-#
-# USB support
-#
-# CONFIG_USB is not set
-
-#
-# Kernel hacking
-#
-CONFIG_FRAME_POINTER=y
-CONFIG_DEBUG_ERRORS=y
-CONFIG_DEBUG_USER=y
-# CONFIG_DEBUG_INFO is not set
-CONFIG_MAGIC_SYSRQ=y
-CONFIG_DEBUG_LL=y

scripts/kconfig/Makefile

@@ -38,7 +38,12 @@ allmodconfig: $(obj)/conf
 	$< -m arch/$(ARCH)/Kconfig
 
 defconfig: $(obj)/conf
+ifeq ($(KBUILD_DEFCONFIG),)
 	$< -d arch/$(ARCH)/Kconfig
+else
+	@echo *** Default configuration is based on '$(KBUILD_DEFCONFIG)'
+	$(Q)$< -D arch/$(ARCH)/configs/$(KBUILD_DEFCONFIG) arch/$(ARCH)/Kconfig
+endif
 
 %_defconfig: $(obj)/conf
 	$(Q)$< -D arch/$(ARCH)/configs/$@ arch/$(ARCH)/Kconfig