Documentation: Make fujitsu/frv/kernel-ABI.txt 80 columns wide

Documentation: Make kernel-ABI.txt 80 columns wide

Note that this only has line-wrapping and white-space changes.
No text was changed at all.

Signed-Off-By: Horms <horms@verge.net.au>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

Documentation/fujitsu/frv/kernel-ABI.txt

@@ -1,17 +1,19 @@
-				 =================================
-				 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.
+			=================================
+			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.
 
 This document has the following sections:
 
@@ -39,7 +41,8 @@ When a system call is made, the following registers are effective:
 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.
 
@@ -47,42 +50,46 @@ The FR-V CPU has three basic operating modes. In order of increasing capability:
 
   (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
@@ -92,10 +99,12 @@ transition prologues.
 	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.
@@ -104,18 +113,21 @@ transition prologues.
 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
 
@@ -124,46 +136,53 @@ Certain registers are also used or modified across function calls:
 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]
 
@@ -176,8 +195,9 @@ What happens is this:
 
 	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)
 
@@ -187,48 +207,56 @@ What happens is this:
 
 	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.