Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial

# This makefile is used to generate the kernel documentation,

# primarily based on in-line comments in various source files.

# See Documentation/kernel-doc-nano-HOWTO.txt for instruction in how

# to ducument the SRC - and how to read it.

# to document the SRC - and how to read it.

# To add a new book the only step required is to add the book to the

# list of DOCBOOKS.

  <chapter id="sysfs">

     <title>The Filesystem for Exporting Kernel Objects</title>

!Efs/sysfs/file.c

!Efs/sysfs/dir.c

!Efs/sysfs/symlink.c

!Efs/sysfs/bin.c

  </chapter>

echo "event_num:event_type:event_argument" > 

	/proc/acpi/hotkey/action.

The result of the execution of this aml method is 

attached to /proc/acpi/hotkey/poll_method, which is dnyamically

attached to /proc/acpi/hotkey/poll_method, which is dynamically

created.  Please use command "cat /proc/acpi/hotkey/polling_method" 

to retrieve it.

			INTERNAL KERNEL ABI FOR FR-V ARCH

			=================================

The internal FRV kernel ABI is not quite the same as the userspace ABI. A number of the registers

are used for special purposed, and the ABI is not consistent between modules vs core, and MMU vs

no-MMU.

This partly stems from the fact that FRV CPUs do not have a separate supervisor stack pointer, and

most of them do not have any scratch registers, thus requiring at least one general purpose

register to be clobbered in such an event. Also, within the kernel core, it is possible to simply

jump or call directly between functions using a relative offset. This cannot be extended to modules

for the displacement is likely to be too far. Thus in modules the address of a function to call

must be calculated in a register and then used, requiring two extra instructions.

The internal FRV kernel ABI is not quite the same as the userspace ABI. A

number of the registers are used for special purposed, and the ABI is not

consistent between modules vs core, and MMU vs no-MMU.

This partly stems from the fact that FRV CPUs do not have a separate

supervisor stack pointer, and most of them do not have any scratch

registers, thus requiring at least one general purpose register to be

clobbered in such an event. Also, within the kernel core, it is possible to

simply jump or call directly between functions using a relative offset.

This cannot be extended to modules for the displacement is likely to be too

far. Thus in modules the address of a function to call must be calculated

in a register and then used, requiring two extra instructions.

This document has the following sections:

CPU OPERATING MODES

===================

The FR-V CPU has three basic operating modes. In order of increasing capability:

The FR-V CPU has three basic operating modes. In order of increasing

capability:

  (1) User mode.

  (2) Kernel mode.

      Normal kernel mode. There are many additional control registers available that may be

      accessed in this mode, in addition to all the stuff available to user mode. This has two

      submodes:

      Normal kernel mode. There are many additional control registers

      available that may be accessed in this mode, in addition to all the

      stuff available to user mode. This has two submodes:

      (a) Exceptions enabled (PSR.T == 1).

      	  Exceptions will invoke the appropriate normal kernel mode handler. On entry to the

      	  handler, the PSR.T bit will be cleared.

	  Exceptions will invoke the appropriate normal kernel mode

	  handler. On entry to the handler, the PSR.T bit will be cleared.

      (b) Exceptions disabled (PSR.T == 0).

      	  No exceptions or interrupts may happen. Any mandatory exceptions will cause the CPU to

      	  halt unless the CPU is told to jump into debug mode instead.

	  No exceptions or interrupts may happen. Any mandatory exceptions

	  will cause the CPU to halt unless the CPU is told to jump into

	  debug mode instead.

  (3) Debug mode.

      No exceptions may happen in this mode. Memory protection and management exceptions will be

      flagged for later consideration, but the exception handler won't be invoked. Debugging traps

      such as hardware breakpoints and watchpoints will be ignored. This mode is entered only by

      debugging events obtained from the other two modes.

      No exceptions may happen in this mode. Memory protection and

      management exceptions will be flagged for later consideration, but

      the exception handler won't be invoked. Debugging traps such as

      hardware breakpoints and watchpoints will be ignored. This mode is

      entered only by debugging events obtained from the other two modes.

      All kernel mode registers may be accessed, plus a few extra debugging specific registers.

      All kernel mode registers may be accessed, plus a few extra debugging

      specific registers.

=================================

INTERNAL KERNEL-MODE REGISTER ABI

=================================

There are a number of permanent register assignments that are set up by entry.S in the exception

prologue. Note that there is a complete set of exception prologues for each of user->kernel

transition and kernel->kernel transition. There are also user->debug and kernel->debug mode

transition prologues.

There are a number of permanent register assignments that are set up by

entry.S in the exception prologue. Note that there is a complete set of

exception prologues for each of user->kernel transition and kernel->kernel

transition. There are also user->debug and kernel->debug mode transition

prologues.

	REGISTER	FLAVOUR	USE

	===============	=======	====================================================

	===============	=======	==============================================

	GR1			Supervisor stack pointer

	GR15			Current thread info pointer

	GR16			GP-Rel base register for small data

	GR31		NOMMU	Destroyed by debug mode entry

	GR31		MMU	Destroyed by TLB miss kernel mode entry

	CCR.ICC2		Virtual interrupt disablement tracking

	CCCR.CC3		Cleared by exception prologue (atomic op emulation)

	CCCR.CC3		Cleared by exception prologue 

				(atomic op emulation)

	SCR0		MMU	See mmu-layout.txt.

	SCR1		MMU	See mmu-layout.txt.

	SCR2		MMU	Save for EAR0 (destroyed by icache insns in debug mode)

	SCR2		MMU	Save for EAR0 (destroyed by icache insns 

					       in debug mode)

	SCR3		MMU	Save for GR31 during debug exceptions

	DAMR/IAMR	NOMMU	Fixed memory protection layout.

	DAMR/IAMR	MMU	See mmu-layout.txt.

Certain registers are also used or modified across function calls:

	REGISTER	CALL				RETURN

	===============	===============================	===============================

	===============	===============================	======================

	GR0		Fixed Zero			-

	GR2		Function call frame pointer

	GR3		Special				Preserved

	GR3-GR7		-				Clobbered

	GR8		Function call arg #1		Return value (or clobbered)

	GR9		Function call arg #2		Return value MSW (or clobbered)

	GR8		Function call arg #1		Return value 

							(or clobbered)

	GR9		Function call arg #2		Return value MSW 

							(or clobbered)

	GR10-GR13	Function call arg #3-#6		Clobbered

	GR14		-				Clobbered

	GR15-GR16	Special				Preserved

	GR17-GR27	-				Preserved

	GR28-GR31	Special				Only accessed explicitly

	GR28-GR31	Special				Only accessed 

							explicitly

	LR		Return address after CALL	Clobbered

	CCR/CCCR	-				Mostly Clobbered

INTERNAL DEBUG-MODE REGISTER ABI

================================

This is the same as the kernel-mode register ABI for functions calls. The difference is that in

debug-mode there's a different stack and a different exception frame. Almost all the global

registers from kernel-mode (including the stack pointer) may be changed.

This is the same as the kernel-mode register ABI for functions calls. The

difference is that in debug-mode there's a different stack and a different

exception frame. Almost all the global registers from kernel-mode

(including the stack pointer) may be changed.

	REGISTER	FLAVOUR	USE

	===============	=======	====================================================

	===============	=======	==============================================

	GR1			Debug stack pointer

	GR16			GP-Rel base register for small data

	GR31			Current debug exception frame pointer (__debug_frame)

	GR31			Current debug exception frame pointer 

				(__debug_frame)

	SCR3		MMU	Saved value of GR31

Note that debug mode is able to interfere with the kernel's emulated atomic ops, so it must be

exceedingly careful not to do any that would interact with the main kernel in this regard. Hence

the debug mode code (gdbstub) is almost completely self-contained. The only external code used is

the sprintf family of functions.

Note that debug mode is able to interfere with the kernel's emulated atomic

ops, so it must be exceedingly careful not to do any that would interact

with the main kernel in this regard. Hence the debug mode code (gdbstub) is

almost completely self-contained. The only external code used is the

sprintf family of functions.

Futhermore, break.S is so complicated because single-step mode does not switch off on entry to an

exception. That means unless manually disabled, single-stepping will blithely go on stepping into

things like interrupts. See gdbstub.txt for more information.

Futhermore, break.S is so complicated because single-step mode does not

switch off on entry to an exception. That means unless manually disabled,

single-stepping will blithely go on stepping into things like interrupts.

See gdbstub.txt for more information.

==========================

VIRTUAL INTERRUPT HANDLING

==========================

Because accesses to the PSR is so slow, and to disable interrupts we have to access it twice (once

to read and once to write), we don't actually disable interrupts at all if we don't have to. What

we do instead is use the ICC2 condition code flags to note virtual disablement, such that if we

then do take an interrupt, we note the flag, really disable interrupts, set another flag and resume

execution at the point the interrupt happened. Setting condition flags as a side effect of an

arithmetic or logical instruction is really fast. This use of the ICC2 only occurs within the

Because accesses to the PSR is so slow, and to disable interrupts we have

to access it twice (once to read and once to write), we don't actually

disable interrupts at all if we don't have to. What we do instead is use

the ICC2 condition code flags to note virtual disablement, such that if we

then do take an interrupt, we note the flag, really disable interrupts, set

another flag and resume execution at the point the interrupt happened.

Setting condition flags as a side effect of an arithmetic or logical

instruction is really fast. This use of the ICC2 only occurs within the

kernel - it does not affect userspace.

The flags we use are:

 (*) CCR.ICC2.Z [Zero flag]

     Set to virtually disable interrupts, clear when interrupts are virtually enabled. Can be

     modified by logical instructions without affecting the Carry flag.

     Set to virtually disable interrupts, clear when interrupts are

     virtually enabled. Can be modified by logical instructions without

     affecting the Carry flag.

 (*) CCR.ICC2.C [Carry flag]

	ICC2.Z is 0, ICC2.C is 1.

 (2) An interrupt occurs. The exception prologue examines ICC2.Z and determines that nothing needs

     doing. This is done simply with an unlikely BEQ instruction.

 (2) An interrupt occurs. The exception prologue examines ICC2.Z and

     determines that nothing needs doing. This is done simply with an

     unlikely BEQ instruction.

 (3) The interrupts are disabled (local_irq_disable)

	ICC2.Z would be set to 0.

     A TIHI #2 instruction (trap #2 if condition HI - Z==0 && C==0) would be used to trap if

     interrupts were now virtually enabled, but physically disabled - which they're not, so the

     trap isn't taken. The kernel would then be back to state (1).

     A TIHI #2 instruction (trap #2 if condition HI - Z==0 && C==0) would

     be used to trap if interrupts were now virtually enabled, but

     physically disabled - which they're not, so the trap isn't taken. The

     kernel would then be back to state (1).

 (5) An interrupt occurs. The exception prologue examines ICC2.Z and determines that the interrupt

     shouldn't actually have happened. It jumps aside, and there disabled interrupts by setting

     PSR.PIL to 14 and then it clears ICC2.C.

 (5) An interrupt occurs. The exception prologue examines ICC2.Z and

     determines that the interrupt shouldn't actually have happened. It

     jumps aside, and there disabled interrupts by setting PSR.PIL to 14

     and then it clears ICC2.C.

 (6) If interrupts were then saved and disabled again (local_irq_save):

	ICC2.Z would be shifted into the save variable and masked off (giving a 1).

	ICC2.Z would be shifted into the save variable and masked off 

	(giving a 1).

	ICC2.Z would then be set to 1 (thus unchanged), and ICC2.C would be unaffected (ie: 0).

	ICC2.Z would then be set to 1 (thus unchanged), and ICC2.C would be

	unaffected (ie: 0).

 (7) If interrupts were then restored from state (6) (local_irq_restore):

	ICC2.Z would be set to indicate the result of XOR'ing the saved value (ie: 1) with 1, which

	gives a result of 0 - thus leaving ICC2.Z set.

	ICC2.Z would be set to indicate the result of XOR'ing the saved

	value (ie: 1) with 1, which gives a result of 0 - thus leaving

	ICC2.Z set.

	ICC2.C would remain unaffected (ie: 0).

     A TIHI #2 instruction would be used to again assay the current state, but this would do

     nothing as Z==1.

     A TIHI #2 instruction would be used to again assay the current state,

     but this would do nothing as Z==1.

 (8) If interrupts were then enabled (local_irq_enable):

	ICC2.Z would be cleared. ICC2.C would be left unaffected. Both flags would now be 0.

	ICC2.Z would be cleared. ICC2.C would be left unaffected. Both

	flags would now be 0.

     A TIHI #2 instruction again issued to assay the current state would then trap as both Z==0

     [interrupts virtually enabled] and C==0 [interrupts really disabled] would then be true.

     A TIHI #2 instruction again issued to assay the current state would

     then trap as both Z==0 [interrupts virtually enabled] and C==0

     [interrupts really disabled] would then be true.

 (9) The trap #2 handler would simply enable hardware interrupts (set PSR.PIL to 0), set ICC2.C to

     1 and return.

 (9) The trap #2 handler would simply enable hardware interrupts 

     (set PSR.PIL to 0), set ICC2.C to 1 and return.

(10) Immediately upon returning, the pending interrupt would be taken.

(11) The interrupt handler would take the path of actually processing the interrupt (ICC2.Z is

     clear, BEQ fails as per step (2)).

(11) The interrupt handler would take the path of actually processing the

     interrupt (ICC2.Z is clear, BEQ fails as per step (2)).

(12) The interrupt handler would then set ICC2.C to 1 since hardware interrupts are definitely

     enabled - or else the kernel wouldn't be here.

(12) The interrupt handler would then set ICC2.C to 1 since hardware

     interrupts are definitely enabled - or else the kernel wouldn't be here.

(13) On return from the interrupt handler, things would be back to state (1).

This trap (#2) is only available in kernel mode. In user mode it will result in SIGILL.

This trap (#2) is only available in kernel mode. In user mode it will

result in SIGILL.

February 2003             Kernel Parameters                     v2.5.59

                          Kernel Parameters

                          ~~~~~~~~~~~~~~~~~

The following is a consolidated list of the kernel parameters as implemented

	usbcore.blinkenlights=1

The text in square brackets at the beginning of the description states the

restrictions on the kernel for the said kernel parameter to be valid. The

restrictions referred to are that the relevant option is valid if:

This document may not be entirely up to date and comprehensive. The command

"modinfo -p ${modulename}" shows a current list of all parameters of a loadable

module. Loadable modules, after being loaded into the running kernel, also

reveal their parameters in /sys/module/${modulename}/parameters/. Some of these

parameters may be changed at runtime by the command

"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".

The parameters listed below are only valid if certain kernel build options were

enabled and if respective hardware is present. The text in square brackets at

the beginning of each description states the restrictions within which a

parameter is applicable:

	ACPI	ACPI support is enabled.

	ALSA	ALSA sound support is enabled.

	noltlbs		[PPC] Do not use large page/tlb entries for kernel

			lowmem mapping on PPC40x.

	nomce		[IA-32] Machine Check Exception

	nomca		[IA-64] Disable machine check abort handling

	nomce		[IA-32] Machine Check Exception

	noresidual	[PPC] Don't use residual data on PReP machines.

	noresume	[SWSUSP] Disables resume and restores original swap

______________________________________________________________________

Changelog:

2000-06-??	Mr. Unknown

	The last known update (for 2.4.0) - the changelog was not kept before.

2002-11-24	Petr Baudis <pasky@ucw.cz>

		Randy Dunlap <randy.dunlap@verizon.net>

	Update for 2.5.49, description for most of the options introduced,

	references to other documentation (C files, READMEs, ..), added S390,

	PPC, SPARC, MTD, ALSA and OSS category. Minor corrections and

	reformatting.

2005-10-19	Randy Dunlap <rdunlap@xenotime.net>

	Lots of typos, whitespace, some reformatting.

TODO: