Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

5 files changed, 670 insertions, 0 deletions

diff --git a/Documentation/ia64/IRQ-redir.txt b/Documentation/ia64/IRQ-redir.txt
new file mode 100644
index 0000000000..f7bd722612
--- /dev/null
+++ b/Documentation/ia64/IRQ-redir.txt
@@ -0,0 +1,69 @@
+IRQ affinity on IA64 platforms
+------------------------------
+                           07.01.2002, Erich Focht <efocht@ess.nec.de>
+
+
+By writing to /proc/irq/IRQ#/smp_affinity the interrupt routing can be
+controlled. The behavior on IA64 platforms is slightly different from
+that described in Documentation/IRQ-affinity.txt for i386 systems.
+
+Because of the usage of SAPIC mode and physical destination mode the
+IRQ target is one particular CPU and cannot be a mask of several
+CPUs. Only the first non-zero bit is taken into account.
+
+
+Usage examples:
+
+The target CPU has to be specified as a hexadecimal CPU mask. The
+first non-zero bit is the selected CPU. This format has been kept for
+compatibility reasons with i386.
+
+Set the delivery mode of interrupt 41 to fixed and route the
+interrupts to CPU #3 (logical CPU number) (2^3=0x08):
+     echo "8" >/proc/irq/41/smp_affinity
+
+Set the default route for IRQ number 41 to CPU 6 in lowest priority
+delivery mode (redirectable):
+     echo "r 40" >/proc/irq/41/smp_affinity
+
+The output of the command
+     cat /proc/irq/IRQ#/smp_affinity
+gives the target CPU mask for the specified interrupt vector. If the CPU
+mask is preceded by the character "r", the interrupt is redirectable
+(i.e. lowest priority mode routing is used), otherwise its route is
+fixed.
+
+
+
+Initialization and default behavior:
+
+If the platform features IRQ redirection (info provided by SAL) all
+IO-SAPIC interrupts are initialized with CPU#0 as their default target
+and the routing is the so called "lowest priority mode" (actually
+fixed SAPIC mode with hint). The XTP chipset registers are used as hints
+for the IRQ routing. Currently in Linux XTP registers can have three
+values:
+        - minimal for an idle task,
+        - normal if any other task runs,
+        - maximal if the CPU is going to be switched off.
+The IRQ is routed to the CPU with lowest XTP register value, the
+search begins at the default CPU. Therefore most of the interrupts
+will be handled by CPU #0.
+
+If the platform doesn't feature interrupt redirection IOSAPIC fixed
+routing is used. The target CPUs are distributed in a round robin
+manner. IRQs will be routed only to the selected target CPUs. Check
+with
+        cat /proc/interrupts
+
+
+
+Comments:
+
+On large (multi-node) systems it is recommended to route the IRQs to
+the node to which the corresponding device is connected.
+For systems like the NEC AzusA we get IRQ node-affinity for free. This
+is because usually the chipsets on each node redirect the interrupts
+only to their own CPUs (as they cannot see the XTP registers on the
+other nodes).
+
diff --git a/Documentation/ia64/README b/Documentation/ia64/README
new file mode 100644
index 0000000000..aa17f2154c
--- /dev/null
+++ b/Documentation/ia64/README
@@ -0,0 +1,43 @@
+        Linux kernel release 2.4.xx for the IA-64 Platform
+
+   These are the release notes for Linux version 2.4 for IA-64
+   platform.  This document provides information specific to IA-64
+   ONLY, to get additional information about the Linux kernel also
+   read the original Linux README provided with the kernel.
+
+INSTALLING the kernel:
+
+ - IA-64 kernel installation is the same as the other platforms, see
+   original README for details.
+
+
+SOFTWARE REQUIREMENTS
+
+   Compiling and running this kernel requires an IA-64 compliant GCC
+   compiler.  And various software packages also compiled with an
+   IA-64 compliant GCC compiler.
+
+
+CONFIGURING the kernel:
+
+   Configuration is the same, see original README for details.
+
+
+COMPILING the kernel:
+
+ - Compiling this kernel doesn't differ from other platform so read
+   the original README for details BUT make sure you have an IA-64
+   compliant GCC compiler.
+
+IA-64 SPECIFICS
+
+ - General issues:
+
+    o Hardly any performance tuning has been done. Obvious targets
+      include the library routines (IP checksum, etc.). Less
+      obvious targets include making sure we don't flush the TLB
+      needlessly, etc.
+
+    o SMP locks cleanup/optimization
+
+    o IA32 support.  Currently experimental.  It mostly works.
diff --git a/Documentation/ia64/efirtc.txt b/Documentation/ia64/efirtc.txt
new file mode 100644
index 0000000000..ede2c1e51c
--- /dev/null
+++ b/Documentation/ia64/efirtc.txt
@@ -0,0 +1,128 @@
+EFI Real Time Clock driver
+-------------------------------
+S. Eranian <eranian@hpl.hp.com>
+March 2000
+
+I/ Introduction
+
+This document describes the efirtc.c driver has provided for
+the IA-64 platform. 
+
+The purpose of this driver is to supply an API for kernel and user applications
+to get access to the Time Service offered by EFI version 0.92.
+
+EFI provides 4 calls one can make once the OS is booted: GetTime(),
+SetTime(), GetWakeupTime(), SetWakeupTime() which are all supported by this
+driver. We describe those calls as well the design of the driver in the
+following sections.
+
+II/ Design Decisions
+
+The original ideas was to provide a very simple driver to get access to, 
+at first, the time of day service. This is required in order to access, in a 
+portable way, the CMOS clock. A program like /sbin/hwclock uses such a clock 
+to initialize the system view of the time during boot.
+
+Because we wanted to minimize the impact on existing user-level apps using
+the CMOS clock, we decided to expose an API that was very similar to the one
+used today with the legacy RTC driver (driver/char/rtc.c). However, because 
+EFI provides a simpler services, not all all ioctl() are available. Also
+new ioctl()s have been introduced for things that EFI provides but not the 
+legacy.
+
+EFI uses a slightly different way of representing the time, noticeably
+the reference date is different. Year is the using the full 4-digit format.
+The Epoch is January 1st 1998. For backward compatibility reasons we don't
+expose this new way of representing time. Instead we use something very 
+similar to the struct tm, i.e. struct rtc_time, as used by hwclock.
+One of the reasons for doing it this way is to allow for EFI to still evolve
+without necessarily impacting any of the user applications. The decoupling
+enables flexibility and permits writing wrapper code is ncase things change.
+
+The driver exposes two interfaces, one via the device file and a set of
+ioctl()s. The other is read-only via the /proc filesystem. 
+
+As of today we don't offer a /proc/sys interface.
+
+To allow for a uniform interface between the legacy RTC and EFI time service,
+we have created the include/linux/rtc.h header file to contain only the 
+"public" API of the two drivers.  The specifics of the legacy RTC are still 
+in include/linux/mc146818rtc.h.
+
+ 
+III/ Time of day service
+
+The part of the driver gives access to the time of day service of EFI.
+Two ioctl()s, compatible with the legacy RTC calls:
+
+        Read the CMOS clock: ioctl(d, RTC_RD_TIME, &rtc);
+
+        Write the CMOS clock: ioctl(d, RTC_SET_TIME, &rtc);
+
+The rtc is a pointer to a data structure defined in rtc.h which is close
+to a struct tm:
+
+struct rtc_time {
+        int tm_sec;
+        int tm_min;
+        int tm_hour;
+        int tm_mday;
+        int tm_mon;
+        int tm_year;
+        int tm_wday;
+        int tm_yday;
+        int tm_isdst;
+};
+
+The driver takes care of converting back an forth between the EFI time and
+this format.
+
+Those two ioctl()s can be exercised with the hwclock command:
+
+For reading:
+# /sbin/hwclock --show
+Mon Mar  6 15:32:32 2000  -0.910248 seconds
+
+For setting:
+# /sbin/hwclock --systohc
+
+Root privileges are required to be able to set the time of day.
+
+IV/ Wakeup Alarm service
+
+EFI provides an API by which one can program when a machine should wakeup,
+i.e. reboot. This is very different from the alarm provided by the legacy
+RTC which is some kind of interval timer alarm. For this reason we don't use
+the same ioctl()s to get access to the service. Instead we have
+introduced 2 news ioctl()s to the interface of an RTC. 
+
+We have added 2 new ioctl()s that are specific to the EFI driver:
+
+        Read the current state of the alarm
+        ioctl(d, RTC_WKLAM_RD, &wkt)
+
+        Set the alarm or change its status
+        ioctl(d, RTC_WKALM_SET, &wkt)
+
+The wkt structure encapsulates a struct rtc_time + 2 extra fields to get 
+status information:
+        
+struct rtc_wkalrm {
+
+        unsigned char enabled; /* =1 if alarm is enabled */
+        unsigned char pending; /* =1 if alarm is pending  */
+
+        struct rtc_time time;
+} 
+
+As of today, none of the existing user-level apps supports this feature.
+However writing such a program should be hard by simply using those two 
+ioctl(). 
+
+Root privileges are required to be able to set the alarm.
+
+V/ References.
+
+Checkout the following Web site for more information on EFI:
+
+http://developer.intel.com/technology/efi/
diff --git a/Documentation/ia64/fsys.txt b/Documentation/ia64/fsys.txt
new file mode 100644
index 0000000000..28da181f99
--- /dev/null
+++ b/Documentation/ia64/fsys.txt
@@ -0,0 +1,286 @@
+-*-Mode: outline-*-
+
+                Light-weight System Calls for IA-64
+                -----------------------------------
+
+                        Started: 13-Jan-2003
+                    Last update: 27-Sep-2003
+
+                      David Mosberger-Tang
+                      <davidm@hpl.hp.com>
+
+Using the "epc" instruction effectively introduces a new mode of
+execution to the ia64 linux kernel.  We call this mode the
+"fsys-mode".  To recap, the normal states of execution are:
+
+  - kernel mode:
+        Both the register stack and the memory stack have been
+        switched over to kernel memory.  The user-level state is saved
+        in a pt-regs structure at the top of the kernel memory stack.
+
+  - user mode:
+        Both the register stack and the kernel stack are in
+        user memory.  The user-level state is contained in the
+        CPU registers.
+
+  - bank 0 interruption-handling mode:
+        This is the non-interruptible state which all
+        interruption-handlers start execution in.  The user-level
+        state remains in the CPU registers and some kernel state may
+        be stored in bank 0 of registers r16-r31.
+
+In contrast, fsys-mode has the following special properties:
+
+  - execution is at privilege level 0 (most-privileged)
+
+  - CPU registers may contain a mixture of user-level and kernel-level
+    state (it is the responsibility of the kernel to ensure that no
+    security-sensitive kernel-level state is leaked back to
+    user-level)
+
+  - execution is interruptible and preemptible (an fsys-mode handler
+    can disable interrupts and avoid all other interruption-sources
+    to avoid preemption)
+
+  - neither the memory-stack nor the register-stack can be trusted while
+    in fsys-mode (they point to the user-level stacks, which may
+    be invalid, or completely bogus addresses)
+
+In summary, fsys-mode is much more similar to running in user-mode
+than it is to running in kernel-mode.  Of course, given that the
+privilege level is at level 0, this means that fsys-mode requires some
+care (see below).
+
+
+* How to tell fsys-mode
+
+Linux operates in fsys-mode when (a) the privilege level is 0 (most
+privileged) and (b) the stacks have NOT been switched to kernel memory
+yet.  For convenience, the header file <asm-ia64/ptrace.h> provides
+three macros:
+
+        user_mode(regs)
+        user_stack(task,regs)
+        fsys_mode(task,regs)
+
+The "regs" argument is a pointer to a pt_regs structure.  The "task"
+argument is a pointer to the task structure to which the "regs"
+pointer belongs to.  user_mode() returns TRUE if the CPU state pointed
+to by "regs" was executing in user mode (privilege level 3).
+user_stack() returns TRUE if the state pointed to by "regs" was
+executing on the user-level stack(s).  Finally, fsys_mode() returns
+TRUE if the CPU state pointed to by "regs" was executing in fsys-mode.
+The fsys_mode() macro is equivalent to the expression:
+
+        !user_mode(regs) && user_stack(task,regs)
+
+* How to write an fsyscall handler
+
+The file arch/ia64/kernel/fsys.S contains a table of fsyscall-handlers
+(fsyscall_table).  This table contains one entry for each system call.
+By default, a system call is handled by fsys_fallback_syscall().  This
+routine takes care of entering (full) kernel mode and calling the
+normal Linux system call handler.  For performance-critical system
+calls, it is possible to write a hand-tuned fsyscall_handler.  For
+example, fsys.S contains fsys_getpid(), which is a hand-tuned version
+of the getpid() system call.
+
+The entry and exit-state of an fsyscall handler is as follows:
+
+** Machine state on entry to fsyscall handler:
+
+ - r10    = 0
+ - r11    = saved ar.pfs (a user-level value)
+ - r15    = system call number
+ - r16    = "current" task pointer (in normal kernel-mode, this is in r13)
+ - r32-r39 = system call arguments
+ - b6     = return address (a user-level value)
+ - ar.pfs = previous frame-state (a user-level value)
+ - PSR.be = cleared to zero (i.e., little-endian byte order is in effect)
+ - all other registers may contain values passed in from user-mode
+
+** Required machine state on exit to fsyscall handler:
+
+ - r11    = saved ar.pfs (as passed into the fsyscall handler)
+ - r15    = system call number (as passed into the fsyscall handler)
+ - r32-r39 = system call arguments (as passed into the fsyscall handler)
+ - b6     = return address (as passed into the fsyscall handler)
+ - ar.pfs = previous frame-state (as passed into the fsyscall handler)
+
+Fsyscall handlers can execute with very little overhead, but with that
+speed comes a set of restrictions:
+
+ o Fsyscall-handlers MUST check for any pending work in the flags
+   member of the thread-info structure and if any of the
+   TIF_ALLWORK_MASK flags are set, the handler needs to fall back on
+   doing a full system call (by calling fsys_fallback_syscall).
+
+ o Fsyscall-handlers MUST preserve incoming arguments (r32-r39, r11,
+   r15, b6, and ar.pfs) because they will be needed in case of a
+   system call restart.  Of course, all "preserved" registers also
+   must be preserved, in accordance to the normal calling conventions.
+
+ o Fsyscall-handlers MUST check argument registers for containing a
+   NaT value before using them in any way that could trigger a
+   NaT-consumption fault.  If a system call argument is found to
+   contain a NaT value, an fsyscall-handler may return immediately
+   with r8=EINVAL, r10=-1.
+
+ o Fsyscall-handlers MUST NOT use the "alloc" instruction or perform
+   any other operation that would trigger mandatory RSE
+   (register-stack engine) traffic.
+
+ o Fsyscall-handlers MUST NOT write to any stacked registers because
+   it is not safe to assume that user-level called a handler with the
+   proper number of arguments.
+
+ o Fsyscall-handlers need to be careful when accessing per-CPU variables:
+   unless proper safe-guards are taken (e.g., interruptions are avoided),
+   execution may be pre-empted and resumed on another CPU at any given
+   time.
+
+ o Fsyscall-handlers must be careful not to leak sensitive kernel'
+   information back to user-level.  In particular, before returning to
+   user-level, care needs to be taken to clear any scratch registers
+   that could contain sensitive information (note that the current
+   task pointer is not considered sensitive: it's already exposed
+   through ar.k6).
+
+ o Fsyscall-handlers MUST NOT access user-memory without first
+   validating access-permission (this can be done typically via
+   probe.r.fault and/or probe.w.fault) and without guarding against
+   memory access exceptions (this can be done with the EX() macros
+   defined by asmmacro.h).
+
+The above restrictions may seem draconian, but remember that it's
+possible to trade off some of the restrictions by paying a slightly
+higher overhead.  For example, if an fsyscall-handler could benefit
+from the shadow register bank, it could temporarily disable PSR.i and
+PSR.ic, switch to bank 0 (bsw.0) and then use the shadow registers as
+needed.  In other words, following the above rules yields extremely
+fast system call execution (while fully preserving system call
+semantics), but there is also a lot of flexibility in handling more
+complicated cases.
+
+* Signal handling
+
+The delivery of (asynchronous) signals must be delayed until fsys-mode
+is exited.  This is acomplished with the help of the lower-privilege
+transfer trap: arch/ia64/kernel/process.c:do_notify_resume_user()
+checks whether the interrupted task was in fsys-mode and, if so, sets
+PSR.lp and returns immediately.  When fsys-mode is exited via the
+"br.ret" instruction that lowers the privilege level, a trap will
+occur.  The trap handler clears PSR.lp again and returns immediately.
+The kernel exit path then checks for and delivers any pending signals.
+
+* PSR Handling
+
+The "epc" instruction doesn't change the contents of PSR at all.  This
+is in contrast to a regular interruption, which clears almost all
+bits.  Because of that, some care needs to be taken to ensure things
+work as expected.  The following discussion describes how each PSR bit
+is handled.
+
+PSR.be  Cleared when entering fsys-mode.  A srlz.d instruction is used
+        to ensure the CPU is in little-endian mode before the first
+        load/store instruction is executed.  PSR.be is normally NOT
+        restored upon return from an fsys-mode handler.  In other
+        words, user-level code must not rely on PSR.be being preserved
+        across a system call.
+PSR.up  Unchanged.
+PSR.ac  Unchanged.
+PSR.mfl Unchanged.  Note: fsys-mode handlers must not write-registers!
+PSR.mfh Unchanged.  Note: fsys-mode handlers must not write-registers!
+PSR.ic  Unchanged.  Note: fsys-mode handlers can clear the bit, if needed.
+PSR.i   Unchanged.  Note: fsys-mode handlers can clear the bit, if needed.
+PSR.pk  Unchanged.
+PSR.dt  Unchanged.
+PSR.dfl Unchanged.  Note: fsys-mode handlers must not write-registers!
+PSR.dfh Unchanged.  Note: fsys-mode handlers must not write-registers!
+PSR.sp  Unchanged.
+PSR.pp  Unchanged.
+PSR.di  Unchanged.
+PSR.si  Unchanged.
+PSR.db  Unchanged.  The kernel prevents user-level from setting a hardware
+        breakpoint that triggers at any privilege level other than 3 (user-mode).
+PSR.lp  Unchanged.
+PSR.tb  Lazy redirect.  If a taken-branch trap occurs while in
+        fsys-mode, the trap-handler modifies the saved machine state
+        such that execution resumes in the gate page at
+        syscall_via_break(), with privilege level 3.  Note: the
+        taken branch would occur on the branch invoking the
+        fsyscall-handler, at which point, by definition, a syscall
+        restart is still safe.  If the system call number is invalid,
+        the fsys-mode handler will return directly to user-level.  This
+        return will trigger a taken-branch trap, but since the trap is
+        taken _after_ restoring the privilege level, the CPU has already
+        left fsys-mode, so no special treatment is needed.
+PSR.rt  Unchanged.
+PSR.cpl Cleared to 0.
+PSR.is  Unchanged (guaranteed to be 0 on entry to the gate page).
+PSR.mc  Unchanged.
+PSR.it  Unchanged (guaranteed to be 1).
+PSR.id  Unchanged.  Note: the ia64 linux kernel never sets this bit.
+PSR.da  Unchanged.  Note: the ia64 linux kernel never sets this bit.
+PSR.dd  Unchanged.  Note: the ia64 linux kernel never sets this bit.
+PSR.ss  Lazy redirect.  If set, "epc" will cause a Single Step Trap to
+        be taken.  The trap handler then modifies the saved machine
+        state such that execution resumes in the gate page at
+        syscall_via_break(), with privilege level 3.
+PSR.ri  Unchanged.
+PSR.ed  Unchanged.  Note: This bit could only have an effect if an fsys-mode
+        handler performed a speculative load that gets NaTted.  If so, this
+        would be the normal & expected behavior, so no special treatment is
+        needed.
+PSR.bn  Unchanged.  Note: fsys-mode handlers may clear the bit, if needed.
+        Doing so requires clearing PSR.i and PSR.ic as well.
+PSR.ia  Unchanged.  Note: the ia64 linux kernel never sets this bit.
+
+* Using fast system calls
+
+To use fast system calls, userspace applications need simply call
+__kernel_syscall_via_epc().  For example
+
+-- example fgettimeofday() call --
+-- fgettimeofday.S --
+
+#include <asm/asmmacro.h>
+
+GLOBAL_ENTRY(fgettimeofday)
+.prologue
+.save ar.pfs, r11
+mov r11 = ar.pfs
+.body 
+
+mov r2 = 0xa000000000020660;;  // gate address 
+                               // found by inspection of System.map for the 
+                               // __kernel_syscall_via_epc() function.  See
+                               // below for how to do this for real.
+
+mov b7 = r2
+mov r15 = 1087                 // gettimeofday syscall
+;;
+br.call.sptk.many b6 = b7
+;;
+
+.restore sp
+
+mov ar.pfs = r11
+br.ret.sptk.many rp;;         // return to caller
+END(fgettimeofday)
+
+-- end fgettimeofday.S --
+
+In reality, getting the gate address is accomplished by two extra
+values passed via the ELF auxiliary vector (include/asm-ia64/elf.h)
+
+ o AT_SYSINFO : is the address of __kernel_syscall_via_epc()
+ o AT_SYSINFO_EHDR : is the address of the kernel gate ELF DSO
+
+The ELF DSO is a pre-linked library that is mapped in by the kernel at
+the gate page.  It is a proper ELF shared object so, with a dynamic
+loader that recognises the library, you should be able to make calls to
+the exported functions within it as with any other shared library.
+AT_SYSINFO points into the kernel DSO at the
+__kernel_syscall_via_epc() function for historical reasons (it was
+used before the kernel DSO) and as a convenience.
diff --git a/Documentation/ia64/serial.txt b/Documentation/ia64/serial.txt
new file mode 100644
index 0000000000..f51eb4bc2f
--- /dev/null
+++ b/Documentation/ia64/serial.txt
@@ -0,0 +1,144 @@
+SERIAL DEVICE NAMING
+
+    As of 2.6.10, serial devices on ia64 are named based on the
+    order of ACPI and PCI enumeration.  The first device in the
+    ACPI namespace (if any) becomes /dev/ttyS0, the second becomes
+    /dev/ttyS1, etc., and PCI devices are named sequentially
+    starting after the ACPI devices.
+
+    Prior to 2.6.10, there were confusing exceptions to this:
+
+        - Firmware on some machines (mostly from HP) provides an HCDP
+          table[1] that tells the kernel about devices that can be used
+          as a serial console.  If the user specified "console=ttyS0"
+          or the EFI ConOut path contained only UART devices, the
+          kernel registered the device described by the HCDP as
+          /dev/ttyS0.
+
+        - If there was no HCDP, we assumed there were UARTs at the
+          legacy COM port addresses (I/O ports 0x3f8 and 0x2f8), so
+          the kernel registered those as /dev/ttyS0 and /dev/ttyS1.
+
+    Any additional ACPI or PCI devices were registered sequentially
+    after /dev/ttyS0 as they were discovered.
+
+    With an HCDP, device names changed depending on EFI configuration
+    and "console=" arguments.  Without an HCDP, device names didn't
+    change, but we registered devices that might not really exist.
+
+    For example, an HP rx1600 with a single built-in serial port
+    (described in the ACPI namespace) plus an MP[2] (a PCI device) has
+    these ports:
+
+                                  pre-2.6.10      pre-2.6.10
+                    MMIO         (EFI console    (EFI console
+                   address        on builtin)     on MP port)    2.6.10
+                  ==========      ==========      ==========     ======
+      builtin     0xff5e0000        ttyS0           ttyS1         ttyS0
+      MP UPS      0xf8031000        ttyS1           ttyS2         ttyS1
+      MP Console  0xf8030000        ttyS2           ttyS0         ttyS2
+      MP 2        0xf8030010        ttyS3           ttyS3         ttyS3
+      MP 3        0xf8030038        ttyS4           ttyS4         ttyS4
+
+CONSOLE SELECTION
+
+    EFI knows what your console devices are, but it doesn't tell the
+    kernel quite enough to actually locate them.  The DIG64 HCDP
+    table[1] does tell the kernel where potential serial console
+    devices are, but not all firmware supplies it.  Also, EFI supports
+    multiple simultaneous consoles and doesn't tell the kernel which
+    should be the "primary" one.
+
+    So how do you tell Linux which console device to use?
+
+        - If your firmware supplies the HCDP, it is simplest to
+          configure EFI with a single device (either a UART or a VGA
+          card) as the console.  Then you don't need to tell Linux
+          anything; the kernel will automatically use the EFI console.
+
+          (This works only in 2.6.6 or later; prior to that you had
+          to specify "console=ttyS0" to get a serial console.)
+
+        - Without an HCDP, Linux defaults to a VGA console unless you
+          specify a "console=" argument.
+
+    NOTE: Don't assume that a serial console device will be /dev/ttyS0.
+    It might be ttyS1, ttyS2, etc.  Make sure you have the appropriate
+    entries in /etc/inittab (for getty) and /etc/securetty (to allow
+    root login).
+
+EARLY SERIAL CONSOLE
+
+    The kernel can't start using a serial console until it knows where
+    the device lives.  Normally this happens when the driver enumerates
+    all the serial devices, which can happen a minute or more after the
+    kernel starts booting.
+
+    2.6.10 and later kernels have an "early uart" driver that works
+    very early in the boot process.  The kernel will automatically use
+    this if the user supplies an argument like "console=uart,io,0x3f8",
+    or if the EFI console path contains only a UART device and the
+    firmware supplies an HCDP.
+
+TROUBLESHOOTING SERIAL CONSOLE PROBLEMS
+
+    No kernel output after elilo prints "Uncompressing Linux... done":
+
+        - You specified "console=ttyS0" but Linux changed the device
+          to which ttyS0 refers.  Configure exactly one EFI console
+          device[3] and remove the "console=" option.
+
+        - The EFI console path contains both a VGA device and a UART.
+          EFI and elilo use both, but Linux defaults to VGA.  Remove
+          the VGA device from the EFI console path[3].
+
+        - Multiple UARTs selected as EFI console devices.  EFI and
+          elilo use all selected devices, but Linux uses only one.
+          Make sure only one UART is selected in the EFI console
+          path[3].
+
+        - You're connected to an HP MP port[2] but have a non-MP UART
+          selected as EFI console device.  EFI uses the MP as a
+          console device even when it isn't explicitly selected.
+          Either move the console cable to the non-MP UART, or change
+          the EFI console path[3] to the MP UART.
+
+    Long pause (60+ seconds) between "Uncompressing Linux... done" and
+    start of kernel output:
+
+        - No early console because you used "console=ttyS<n>".  Remove
+          the "console=" option if your firmware supplies an HCDP.
+
+        - If you don't have an HCDP, the kernel doesn't know where
+          your console lives until the driver discovers serial
+          devices.  Use "console=uart, io,0x3f8" (or appropriate
+          address for your machine).
+
+    Kernel and init script output works fine, but no "login:" prompt:
+
+        - Add getty entry to /etc/inittab for console tty.  Look for
+          the "Adding console on ttyS<n>" message that tells you which
+          device is the console.
+
+    "login:" prompt, but can't login as root:
+
+        - Add entry to /etc/securetty for console tty.
+
+
+
+[1] http://www.dig64.org/specifications/DIG64_PCDPv20.pdf
+    The table was originally defined as the "HCDP" for "Headless
+    Console/Debug Port."  The current version is the "PCDP" for
+    "Primary Console and Debug Port Devices."
+
+[2] The HP MP (management processor) is a PCI device that provides
+    several UARTs.  One of the UARTs is often used as a console; the
+    EFI Boot Manager identifies it as "Acpi(HWP0002,700)/Pci(...)/Uart".
+    The external connection is usually a 25-pin connector, and a
+    special dongle converts that to three 9-pin connectors, one of
+    which is labelled "Console."
+
+[3] EFI console devices are configured using the EFI Boot Manager
+    "Boot option maintenance" menu.  You may have to interrupt the
+    boot sequence to use this menu, and you will have to reset the
+    box after changing console configuration.