2.6.3-rc3 serial console woes

[Keith Owens <kaos@sgi.com>]

Between 2.6.3-rc2 and 2.6.3-rc3, the serial console initialisation
changed, due to this patch :-

  http://linux.bkbits.net:8080/linux-2.5/cset@1.1653?nav=index.html|ChangeSet@-7d

Now the serial console is not initialised until a long way into the
boot, just after the disks are probed.  This makes it impossible to use
a kernel debugger such as kdb or kgdb over a serial console during
device initialisation.

You get no serial console output until after devices have been probed.
So if something goes wrong during boot, you have no indication of the
problem.  Even without device problems, the delay on serial console
output can make it look like the machine has hung, with no output on
the serial console until a couple of minutes after boot.

.config extract

X86=y
MMU=y
UID16=y
GENERIC_ISA_DMA=y
EXPERIMENTAL=y
CLEAN_COMPILE=y
STANDALONE=y
SWAP=y
SYSVIPC=y
SYSCTL=y
LOG_BUF_SHIFT=16
KALLSYMS=y
FUTEX=y
EPOLL=y
IOSCHED_NOOP=y
IOSCHED_AS=y
IOSCHED_DEADLINE=y
MODULES=y
OBSOLETE_MODPARM=y
KMOD=y
X86_PC=y
M686=y
X86_CMPXCHG=y
X86_XADD=y
X86_L1_CACHE_SHIFT=5
RWSEM_XCHGADD_ALGORITHM=y
X86_PPRO_FENCE=y
X86_WP_WORKS_OK=y
X86_INVLPG=y
X86_BSWAP=y
X86_POPAD_OK=y
X86_GOOD_APIC=y
X86_USE_PPRO_CHECKSUM=y
SMP=y
NR_CPUS=2
X86_LOCAL_APIC=y
X86_IO_APIC=y
X86_TSC=y
X86_MCE=y
X86_MSR=m
X86_CPUID=m
NOHIGHMEM=y
MTRR=y
HAVE_DEC_LOCK=y
ACPI_BOOT=y
PCI=y
PCI_GOANY=y
PCI_BIOS=y
PCI_DIRECT=y
PCI_NAMES=y
ISA=y
BINFMT_ELF=y
BINFMT_AOUT=m
BINFMT_MISC=m
PARPORT=m
PARPORT_PC=m
PARPORT_PC_CML1=m
BLK_DEV_FD=y
BLK_DEV_LOOP=m
BLK_DEV_RAM=y
BLK_DEV_RAM_SIZE=4096
IDE=y
BLK_DEV_IDE=y
BLK_DEV_IDEDISK=y
BLK_DEV_IDECD=y
BLK_DEV_IDESCSI=y
IDE_GENERIC=y
BLK_DEV_IDEPCI=y
IDEPCI_SHARE_IRQ=y
BLK_DEV_IDEDMA_PCI=y
IDEDMA_PCI_AUTO=y
BLK_DEV_ADMA=y
BLK_DEV_HPT366=y
BLK_DEV_PIIX=y
BLK_DEV_IDEDMA=y
IDEDMA_AUTO=y
SCSI=y
SCSI_PROC_FS=y
BLK_DEV_SD=y
BLK_DEV_SR=m
BLK_DEV_SR_VENDOR=y
CHR_DEV_SG=m
SCSI_REPORT_LUNS=y
SCSI_CONSTANTS=y
SCSI_LOGGING=y
SCSI_AHA1542=m
SCSI_SYM53C8XX_2=y
SCSI_SYM53C8XX_DMA_ADDRESSING_MODE=1
SCSI_SYM53C8XX_DEFAULT_TAGS=16
SCSI_SYM53C8XX_MAX_TAGS=64
SCSI_QLA2XXX=y
NET=y
PACKET=m
NETLINK_DEV=m
UNIX=y
INET=y
INET_ECN=y
SYN_COOKIES=y
NETFILTER=y
IP_NF_CONNTRACK=m
IP_NF_FTP=m
IP_NF_IRC=m
IP_NF_QUEUE=m
IP_NF_IPTABLES=m
IP_NF_MATCH_LIMIT=m
IP_NF_MATCH_MAC=m
IP_NF_MATCH_PKTTYPE=m
IP_NF_MATCH_MARK=m
IP_NF_MATCH_MULTIPORT=m
IP_NF_MATCH_TOS=m
IP_NF_MATCH_ECN=m
IP_NF_MATCH_DSCP=m
IP_NF_MATCH_AH_ESP=m
IP_NF_MATCH_LENGTH=m
IP_NF_MATCH_TTL=m
IP_NF_MATCH_TCPMSS=m
IP_NF_MATCH_HELPER=m
IP_NF_MATCH_STATE=m
IP_NF_MATCH_CONNTRACK=m
IP_NF_MATCH_OWNER=m
IP_NF_FILTER=m
IP_NF_TARGET_REJECT=m
IP_NF_NAT=m
IP_NF_NAT_NEEDED=y
IP_NF_TARGET_MASQUERADE=m
IP_NF_TARGET_REDIRECT=m
IP_NF_NAT_LOCAL=y
IP_NF_NAT_IRC=m
IP_NF_NAT_FTP=m
IP_NF_MANGLE=m
IP_NF_TARGET_TOS=m
IP_NF_TARGET_ECN=m
IP_NF_TARGET_DSCP=m
IP_NF_TARGET_MARK=m
IP_NF_TARGET_LOG=m
IP_NF_TARGET_ULOG=m
IP_NF_TARGET_TCPMSS=m
IP_NF_ARPTABLES=m
IP_NF_ARPFILTER=m
IP_NF_COMPAT_IPCHAINS=m
IP_NF_COMPAT_IPFWADM=m
IPV6_SCTP__=y
NETDEVICES=y
DUMMY=m
ETHERTAP=m
NET_ETHERNET=y
NET_TULIP=y
TULIP=m
NET_ISA=y
NE2000=m
NET_PCI=y
PLIP=m
PPP=m
PPP_ASYNC=m
PPP_DEFLATE=m
PPP_BSDCOMP=m
SLIP=m
SLIP_COMPRESSED=y
INPUT=y
INPUT_MOUSEDEV=y
INPUT_MOUSEDEV_PSAUX=y
INPUT_MOUSEDEV_SCREEN_X=1024
INPUT_MOUSEDEV_SCREEN_Y=768
SOUND_GAMEPORT=y
SERIO=y
SERIO_I8042=y
SERIO_SERPORT=y
INPUT_KEYBOARD=y
KEYBOARD_ATKBD=y
INPUT_MOUSE=y
MOUSE_PS2=y
VT=y
VT_CONSOLE=y
HW_CONSOLE=y
SERIAL_8250=y
SERIAL_8250_CONSOLE=y
SERIAL_8250_NR_UARTS=4
SERIAL_CORE=y
SERIAL_CORE_CONSOLE=y
UNIX98_PTYS=y
UNIX98_PTY_COUNT=256
PRINTER=m
LP_CONSOLE=y
NVRAM=m
RTC=y
VGA_CONSOLE=y
DUMMY_CONSOLE=y
SOUND=m
EXT2_FS=y
XFS_FS=y
XFS_QUOTA=y
MINIX_FS=m
ROMFS_FS=m
QUOTACTL=y
AUTOFS_FS=m
AUTOFS4_FS=m
ISO9660_FS=m
JOLIET=y
ZISOFS=y
ZISOFS_FS=m
FAT_FS=m
MSDOS_FS=m
VFAT_FS=m
NTFS_FS=m
PROC_FS=y
PROC_KCORE=y
DEVPTS_FS=y
TMPFS=y
RAMFS=y
HPFS_FS=m
NFS_FS=m
NFS_V3=y
NFSD=m
NFSD_V3=y
LOCKD=m
LOCKD_V4=y
EXPORTFS=m
SUNRPC=m
SMB_FS=m
MSDOS_PARTITION=y
NLS=y
NLS_DEFAULT="iso8859-1"
DEBUG_KERNEL=y
DEBUG_SLAB=y
MAGIC_SYSRQ=y
KDB=y
KDB_MODULES=m
KDB_CONTINUE_CATASTROPHIC=0
X86_FIND_SMP_CONFIG=y
X86_MPPARSE=y
CRC32=m
ZLIB_INFLATE=m
ZLIB_DEFLATE=m
X86_SMP=y
X86_HT=y
X86_BIOS_REBOOT=y
X86_TRAMPOLINE=y
PC=y