Subject: [PATCH] FRV: Use virtual interrupt disablement
Newsgroups: gmane.linux.kernel
Date: 2006-02-14 16:40:06 GMT (3 years, 20 weeks, 12 hours and 14 minutes ago)
The attached patch makes the FRV arch use virtual interrupt disablement because
accesses to the processor status register (PSR) are relatively slow and because
we will soon have the need to deal with multiple interrupt controls at the same
time (separate h/w and inter-core interrupts).
The way this is done is to dedicate one of the four integer condition code
registers (ICC2) to maintaining a virtual interrupt disablement state whilst
inside the kernel. This uses the ICC2.Z flag (Zero) to indicate whether the
interrupts are virtually disabled and the ICC2.C flag (Carry) to indicate
whether the interrupts are physically disabled.
ICC2.Z is set to indicate interrupts are virtually disabled. ICC2.C is set to
indicate interrupts are physically enabled. Under normal running conditions
Z==0 and C==1.
Disabling interrupts with local_irq_disable() doesn't then actually physically
disable interrupts - it merely sets ICC2.Z to 1. Should an interrupt then
happen, the exception prologue will note ICC2.Z is set and branch out of line
using one instruction (an unlikely BEQ). Here it will physically disable
interrupts and clear ICC2.C.
When it comes time to enable interrupts (local_irq_enable()), this simply
clears the ICC2.Z flag and invokes a trap #2 if both Z and C flags are clear
(the HI integer condition). This can be done with the TIHI conditional trap
instruction.
The trap then physically reenables interrupts and sets ICC2.C again. Upon
returning the interrupt will be taken as interrupts will then be enabled. Note
that whilst processing the trap, the whole exceptions system is disabled, and
so an interrupt can't happen till it returns.
If no pending interrupt had happened, ICC2.C would still be set, the HI
condition would not be fulfilled, and no trap will happen.
Saving interrupts (local_irq_save) is simply a matter of pulling the ICC2.Z
flag out of the CCR register, shifting it down and masking it off. This gives a
result of 0 if interrupts were enabled and 1 if they weren't.
Restoring interrupts (local_irq_restore) is then a matter of taking the saved
value mentioned previously and XOR'ing it against 1. If it was one, the result
will be zero, and if it was zero the result will be non-zero. This result is
then used to affect the ICC2.Z flag directly (it is a condition code flag after
all). An XOR instruction does not affect the Carry flag, and so that bit of
state is unchanged. The two flags can then be sampled to see if they're both
zero using the trap (TIHI) as for the unconditional reenablement
(local_irq_enable).
This patch also:
(1) Modifies the debugging stub (break.S) to handle single-stepping crossing
into the trap #2 handler and into virtually disabled interrupts.
(2) Removes superseded fixup pointers from the second instructions in the trap
tables (there's no a separate fixup table for this).
(3) Declares the trap #3 vector for use in .org directives in the trap table.
(4) Moves irq_enter() and irq_exit() in do_IRQ() to avoid problems with
virtual interrupt handling, and removes the duplicate code that has now
been folded into irq_exit() (softirq and preemption handling).
(5) Tells the compiler in the arch Makefile that ICC2 is now reserved.
(6) Documents the in-kernel ABI, including the virtual interrupts.
(7) Renames the old irq management functions to different names.
Signed-Off-By: David Howells <dhowells <at> redhat.com>
---
warthog>diffstat -p1 frv-virq-2616rc2-2.diff
Documentation/fujitsu/frv/kernel-ABI.txt | 234 +++++++++++++++++++++++++++++++
arch/frv/Makefile | 2
arch/frv/boot/Image |binary
arch/frv/kernel/break.S | 77 +++++++++-
arch/frv/kernel/entry-table.S | 39 ++++-
arch/frv/kernel/entry.S | 65 +++++++-
arch/frv/kernel/head.S | 3
arch/frv/kernel/irq.c | 41 -----
include/asm-frv/spr-regs.h | 1
include/asm-frv/system.h | 88 ++++++++++-
10 files changed, 489 insertions(+), 61 deletions(-)
Binary files linux-2.6.16-rc2-frv/arch/frv/boot/Image and
linux-2.6.16-rc2-frv-int/arch/frv/boot/Image differ
diff -uNrp linux-2.6.16-rc2-frv/arch/frv/kernel/break.S linux-2.6.16-rc2-frv-int/arch/frv/kernel/break.S
--- linux-2.6.16-rc2-frv/arch/frv/kernel/break.S 2005-03-02 12:07:44.000000000 +0000
+++ linux-2.6.16-rc2-frv-int/arch/frv/kernel/break.S 2006-02-14 14:23:11.000000000 +0000
@@ -200,12 +200,20 @@ __break_step:
movsg bpcsr,gr2
sethi.p %hi(__entry_kernel_external_interrupt),gr3
setlo %lo(__entry_kernel_external_interrupt),gr3
- subcc gr2,gr3,gr0,icc0
+ subcc.p gr2,gr3,gr0,icc0
+ sethi %hi(__entry_uspace_external_interrupt),gr3
+ setlo.p %lo(__entry_uspace_external_interrupt),gr3
beq icc0,#2,__break_step_kernel_external_interrupt
- sethi.p %hi(__entry_uspace_external_interrupt),gr3
- setlo %lo(__entry_uspace_external_interrupt),gr3
- subcc gr2,gr3,gr0,icc0
+ subcc.p gr2,gr3,gr0,icc0
+ sethi %hi(__entry_kernel_external_interrupt_virtually_disabled),gr3
+ setlo.p %lo(__entry_kernel_external_interrupt_virtually_disabled),gr3
beq icc0,#2,__break_step_uspace_external_interrupt
+ subcc.p gr2,gr3,gr0,icc0
+ sethi %hi(__entry_kernel_external_interrupt_virtual_reenable),gr3
+ setlo.p %lo(__entry_kernel_external_interrupt_virtual_reenable),gr3
+ beq icc0,#2,__break_step_kernel_external_interrupt_virtually_disabled
+ subcc gr2,gr3,gr0,icc0
+ beq icc0,#2,__break_step_kernel_external_interrupt_virtual_reenable
LEDS 0x2007,gr2
@@ -254,6 +262,9 @@ __break_step_kernel_softprog_interrupt:
# step through an external interrupt from kernel mode
.globl __break_step_kernel_external_interrupt
__break_step_kernel_external_interrupt:
+ # deal with virtual interrupt disablement
+ beq icc2,#0,__break_step_kernel_external_interrupt_virtually_disabled
+
sethi.p %hi(__entry_kernel_external_interrupt_reentry),gr3
setlo %lo(__entry_kernel_external_interrupt_reentry),gr3
@@ -294,6 +305,64 @@ __break_return_as_kernel_prologue:
#endif
rett #1
+# we single-stepped into an interrupt handler whilst interrupts were merely virtually disabled
+# need to really disable interrupts, set flag, fix up and return
+__break_step_kernel_external_interrupt_virtually_disabled:
+ movsg psr,gr2
+ andi gr2,#~PSR_PIL,gr2
+ ori gr2,#PSR_PIL_14,gr2 /* debugging interrupts only */
+ movgs gr2,psr
+
+ ldi @(gr31,#REG_CCR),gr3
+ movgs gr3,ccr
+ subcc.p gr0,gr0,gr0,icc2 /* leave Z set, clear C */
+
+ # exceptions must've been enabled and we must've been in supervisor mode
+ setlos BPSR_BET|BPSR_BS,gr3
+ movgs gr3,bpsr
+
+ # return to where the interrupt happened
+ movsg pcsr,gr2
+ movgs gr2,bpcsr
+
+ lddi.p @(gr31,#REG_GR(2)),gr2
+
+ xor gr31,gr31,gr31
+ movgs gr0,brr
+#ifdef CONFIG_MMU
+ movsg scr3,gr31
+#endif
+ rett #1
+
+# we stepped through into the virtual interrupt reenablement trap
+#
+# we also want to single step anyway, but after fixing up so that we get an event on the
+# instruction after the broken-into exception returns
+ .globl __break_step_kernel_external_interrupt_virtual_reenable
+__break_step_kernel_external_interrupt_virtual_reenable:
+ movsg psr,gr2
+ andi gr2,#~PSR_PIL,gr2
+ movgs gr2,psr
+
+ ldi @(gr31,#REG_CCR),gr3
+ movgs gr3,ccr
+ subicc gr0,#1,gr0,icc2 /* clear Z, set C */
+
+ # save the adjusted ICC2
+ movsg ccr,gr3
+ sti gr3,@(gr31,#REG_CCR)
+
+ # exceptions must've been enabled and we must've been in supervisor mode
+ setlos BPSR_BET|BPSR_BS,gr3
+ movgs gr3,bpsr
+
+ # return to where the trap happened
+ movsg pcsr,gr2
+ movgs gr2,bpcsr
+
+ # and then process the single step
+ bra __break_continue
+
# step through an internal exception from uspace mode
.globl __break_step_uspace_softprog_interrupt
__break_step_uspace_softprog_interrupt:
diff -uNrp linux-2.6.16-rc2-frv/arch/frv/kernel/entry.S linux-2.6.16-rc2-frv-int/arch/frv/kernel/entry.S
--- linux-2.6.16-rc2-frv/arch/frv/kernel/entry.S 2006-02-07 18:37:39.000000000 +0000
+++ linux-2.6.16-rc2-frv-int/arch/frv/kernel/entry.S 2006-02-14 13:55:08.000000000 +0000
@@ -141,7 +141,10 @@ __entry_uspace_external_interrupt_reentr
movsg gner0,gr4
movsg gner1,gr5
- stdi gr4,@(gr28,#REG_GNER0)
+ stdi.p gr4,@(gr28,#REG_GNER0)
+
+ # interrupts start off fully disabled in the interrupt handler
+ subcc gr0,gr0,gr0,icc2 /* set Z and clear C */
# set up kernel global registers
sethi.p %hi(__kernel_current_task),gr5
@@ -193,9 +196,8 @@ __entry_uspace_external_interrupt_reentr
.type __entry_kernel_external_interrupt,@function
__entry_kernel_external_interrupt:
LEDS 0x6210
-
- sub sp,gr15,gr31
- LEDS32
+// sub sp,gr15,gr31
+// LEDS32
# set up the stack pointer
or.p sp,gr0,gr30
@@ -231,7 +233,10 @@ __entry_kernel_external_interrupt_reentr
stdi gr24,@(gr28,#REG_GR(24))
stdi gr26,@(gr28,#REG_GR(26))
sti gr29,@(gr28,#REG_GR(29))
- stdi gr30,@(gr28,#REG_GR(30))
+ stdi.p gr30,@(gr28,#REG_GR(30))
+
+ # note virtual interrupts will be fully enabled upon return
+ subicc gr0,#1,gr0,icc2 /* clear Z, set C */
movsg tbr ,gr20
movsg psr ,gr22
@@ -267,7 +272,10 @@ __entry_kernel_external_interrupt_reentr
movsg gner0,gr4
movsg gner1,gr5
- stdi gr4,@(gr28,#REG_GNER0)
+ stdi.p gr4,@(gr28,#REG_GNER0)
+
+ # interrupts start off fully disabled in the interrupt handler
+ subcc gr0,gr0,gr0,icc2 /* set Z and clear C */
# set the return address
sethi.p %hi(__entry_return_from_kernel_interrupt),gr4
@@ -291,6 +299,45 @@ __entry_kernel_external_interrupt_reentr
.size __entry_kernel_external_interrupt,.-__entry_kernel_external_interrupt
+###############################################################################
+#
+# deal with interrupts that were actually virtually disabled
+# - we need to really disable them, flag the fact and return immediately
+# - if you change this, you must alter break.S also
+#
+###############################################################################
+ .balign L1_CACHE_BYTES
+ .globl __entry_kernel_external_interrupt_virtually_disabled
+ .type __entry_kernel_external_interrupt_virtually_disabled,@function
+__entry_kernel_external_interrupt_virtually_disabled:
+ movsg psr,gr30
+ andi gr30,#~PSR_PIL,gr30
+ ori gr30,#PSR_PIL_14,gr30 ; debugging interrupts only
+ movgs gr30,psr
+ subcc gr0,gr0,gr0,icc2 ; leave Z set, clear C
+ rett #0
+
+ .size __entry_kernel_external_interrupt_virtually_disabled,.-__entry_kernel_external_interrupt_virtually_disabled
+
+###############################################################################
+#
+# deal with re-enablement of interrupts that were pending when virtually re-enabled
+# - set ICC2.C, re-enable the real interrupts and return
+# - we can clear ICC2.Z because we shouldn't be here if it's not 0 [due to TIHI]
+# - if you change this, you must alter break.S also
+#
+###############################################################################
+ .balign L1_CACHE_BYTES
+ .globl __entry_kernel_external_interrupt_virtual_reenable
+ .type __entry_kernel_external_interrupt_virtual_reenable,@function
+__entry_kernel_external_interrupt_virtual_reenable:
+ movsg psr,gr30
+ andi gr30,#~PSR_PIL,gr30 ; re-enable interrupts
+ movgs gr30,psr
+ subicc gr0,#1,gr0,icc2 ; clear Z, set C
+ rett #0
+
+ .size __entry_kernel_external_interrupt_virtual_reenable,.-__entry_kernel_external_interrupt_virtual_reenable
###############################################################################
#
@@ -335,6 +382,7 @@ __entry_uspace_softprog_interrupt_reentr
sethi.p %hi(__entry_return_from_user_exception),gr23
setlo %lo(__entry_return_from_user_exception),gr23
+
bra __entry_common
.size __entry_uspace_softprog_interrupt,.-__entry_uspace_softprog_interrupt
@@ -495,7 +543,10 @@ __entry_common:
movsg gner0,gr4
movsg gner1,gr5
- stdi gr4,@(gr28,#REG_GNER0)
+ stdi.p gr4,@(gr28,#REG_GNER0)
+
+ # set up virtual interrupt disablement
+ subicc gr0,#1,gr0,icc2 /* clear Z flag, set C flag */
# set up kernel global registers
sethi.p %hi(__kernel_current_task),gr5
diff -uNrp linux-2.6.16-rc2-frv/arch/frv/kernel/entry-table.S linux-2.6.16-rc2-frv-int/arch/frv/kernel/entry-table.S
--- linux-2.6.16-rc2-frv/arch/frv/kernel/entry-table.S 2005-03-02 12:07:44.000000000 +0000
+++ linux-2.6.16-rc2-frv-int/arch/frv/kernel/entry-table.S 2006-02-14 14:05:04.000000000 +0000
@@ -116,6 +116,8 @@ __break_kerneltrap_fixup_table:
.long __break_step_uspace_external_interrupt
.section .trap.kernel
.org \tbr_tt
+ # deal with virtual interrupt disablement
+ beq icc2,#0,__entry_kernel_external_interrupt_virtually_disabled
bra __entry_kernel_external_interrupt
.section .trap.fixup.kernel
.org \tbr_tt >> 2
@@ -259,25 +261,52 @@ __trap_fixup_kernel_data_tlb_miss:
.org TBR_TT_TRAP0
.rept 127
bra __entry_uspace_softprog_interrupt
- bra __break_step_uspace_softprog_interrupt
- .long 0,0
+ .long 0,0,0
.endr
.org TBR_TT_BREAK
bra __entry_break
.long 0,0,0
+ .section .trap.fixup.user
+ .org TBR_TT_TRAP0 >> 2
+ .rept 127
+ .long __break_step_uspace_softprog_interrupt
+ .endr
+ .org TBR_TT_BREAK >> 2
+ .long 0
+
# miscellaneous kernel mode entry points
.section .trap.kernel
.org TBR_TT_TRAP0
- .rept 127
bra __entry_kernel_softprog_interrupt
- bra __break_step_kernel_softprog_interrupt
- .long 0,0
+ .org TBR_TT_TRAP1
+ bra __entry_kernel_softprog_interrupt
+
+ # trap #2 in kernel - reenable interrupts
+ .org TBR_TT_TRAP2
+ bra __entry_kernel_external_interrupt_virtual_reenable
+
+ # miscellaneous kernel traps
+ .org TBR_TT_TRAP3
+ .rept 124
+ bra __entry_kernel_softprog_interrupt
+ .long 0,0,0
.endr
.org TBR_TT_BREAK
bra __entry_break
.long 0,0,0
+ .section .trap.fixup.kernel
+ .org TBR_TT_TRAP0 >> 2
+ .long __break_step_kernel_softprog_interrupt
+ .long __break_step_kernel_softprog_interrupt
+ .long __break_step_kernel_external_interrupt_virtual_reenable
+ .rept 124
+ .long __break_step_kernel_softprog_interrupt
+ .endr
+ .org TBR_TT_BREAK >> 2
+ .long 0
+
# miscellaneous debug mode entry points
.section .trap.break
.org TBR_TT_BREAK
diff -uNrp linux-2.6.16-rc2-frv/arch/frv/kernel/head.S linux-2.6.16-rc2-frv-int/arch/frv/kernel/head.S
--- linux-2.6.16-rc2-frv/arch/frv/kernel/head.S 2005-03-02 12:07:44.000000000 +0000
+++ linux-2.6.16-rc2-frv-int/arch/frv/kernel/head.S 2006-02-10 14:14:38.000000000 +0000
@@ -513,6 +513,9 @@ __head_mmu_enabled:
movgs gr0,ccr
movgs gr0,cccr
+ # initialise the virtual interrupt handling
+ subcc gr0,gr0,gr0,icc2 /* set Z, clear C */
+
#ifdef CONFIG_MMU
movgs gr3,scr2
movgs gr3,scr3
diff -uNrp linux-2.6.16-rc2-frv/arch/frv/kernel/irq.c linux-2.6.16-rc2-frv-int/arch/frv/kernel/irq.c
--- linux-2.6.16-rc2-frv/arch/frv/kernel/irq.c 2006-02-06 15:25:19.000000000 +0000
+++ linux-2.6.16-rc2-frv-int/arch/frv/kernel/irq.c 2006-02-14 14:30:53.000000000 +0000
@@ -287,18 +287,11 @@ asmlinkage void do_IRQ(void)
struct irq_source *source;
int level, cpu;
+ irq_enter();
+
level = (__frame->tbr >> 4) & 0xf;
cpu = smp_processor_id();
-#if 0
- {
- static u32 irqcount;
- *(volatile u32 *) 0xe1200004 = ~((irqcount++ << 8) | level);
- *(volatile u16 *) 0xffc00100 = (u16) ~0x9999;
- mb();
- }
-#endif
-
if ((unsigned long) __frame - (unsigned long) (current + 1) < 512)
BUG();
@@ -308,40 +301,12 @@ asmlinkage void do_IRQ(void)
kstat_this_cpu.irqs[level]++;
- irq_enter();
-
for (source = frv_irq_levels[level].sources; source; source = source->next)
source->doirq(source);
- irq_exit();
-
__clr_MASK(level);
- /* only process softirqs if we didn't interrupt another interrupt handler */
- if ((__frame->psr & PSR_PIL) == PSR_PIL_0)
- if (local_softirq_pending())
- do_softirq();
-
-#ifdef CONFIG_PREEMPT
- local_irq_disable();
- while (--current-≥preempt_count == 0) {
- if (!(__frame->psr & PSR_S) ||
- current->need_resched == 0 ||
- in_interrupt())
- break;
- current->preempt_count++;
- local_irq_enable();
- preempt_schedule();
- local_irq_disable();
- }
-#endif
-
-#if 0
- {
- *(volatile u16 *) 0xffc00100 = (u16) ~0x6666;
- mb();
- }
-#endif
+ irq_exit();
} /* end do_IRQ() */
diff -uNrp linux-2.6.16-rc2-frv/arch/frv/Makefile linux-2.6.16-rc2-frv-int/arch/frv/Makefile
--- linux-2.6.16-rc2-frv/arch/frv/Makefile 2006-02-06 15:25:19.000000000 +0000
+++ linux-2.6.16-rc2-frv-int/arch/frv/Makefile 2006-02-09 19:55:12.000000000 +0000
@@ -81,7 +81,7 @@ endif
# - reserve CC3 for use with atomic ops
# - all the extra registers are dealt with only at context switch time
CFLAGS += -mno-fdpic -mgpr-32 -msoft-float -mno-media
-CFLAGS += -ffixed-fcc3 -ffixed-cc3 -ffixed-gr15
+CFLAGS += -ffixed-fcc3 -ffixed-cc3 -ffixed-gr15 -ffixed-icc2
AFLAGS += -mno-fdpic
ASFLAGS += -mno-fdpic
diff -uNrp linux-2.6.16-rc2-frv/Documentation/fujitsu/frv/kernel-ABI.txt linux-2.6.16-rc2-frv-int/Documentation/fujitsu/frv/kernel-ABI.txt
--- linux-2.6.16-rc2-frv/Documentation/fujitsu/frv/kernel-ABI.txt 1970-01-01
01:00:00.000000000 +0100
+++ linux-2.6.16-rc2-frv-int/Documentation/fujitsu/frv/kernel-ABI.txt 2006-02-14
16:19:09.000000000 +0000
@@ -0,0 +1,234 @@
+ =================================
+ 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:
+
+ (*) System call register ABI
+ (*) CPU operating modes
+ (*) Internal kernel-mode register ABI
+ (*) Internal debug-mode register ABI
+ (*) Virtual interrupt handling
+
+
+========================
+SYSTEM CALL REGISTER ABI
+========================
+
+When a system call is made, the following registers are effective:
+
+ REGISTERS CALL RETURN
+ =============== ======================= =======================
+ GR7 System call number Preserved
+ GR8 Syscall arg #1 Return value
+ GR9-GR13 Syscall arg #2-6 Preserved
+
+
+===================
+CPU OPERATING MODES
+===================
+
+The FR-V CPU has three basic operating modes. In order of increasing capability:
+
+ (1) User mode.
+
+ Basic userspace running 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:
+
+ (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.
+
+ (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.
+
+ (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.
+
+ 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.
+
+
+ REGISTER FLAVOUR USE
+ =============== ======= ====================================================
+ GR1 Supervisor stack pointer
+ GR15 Current thread info pointer
+ GR16 GP-Rel base register for small data
+ GR28 Current exception frame pointer (__frame)
+ GR29 Current task pointer (current)
+ GR30 Destroyed by kernel mode entry
+ 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)
+ SCR0 MMU See mmu-layout.txt.
+ SCR1 MMU See mmu-layout.txt.
+ 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)
+ GR10-GR13 Function call arg #3-#6 Clobbered
+ GR14 - Clobbered
+ GR15-GR16 Special Preserved
+ GR17-GR27 - Preserved
+ 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.
+
+ REGISTER FLAVOUR USE
+ =============== ======= ====================================================
+ GR1 Debug stack pointer
+ GR16 GP-Rel base register for small data
+ 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.
+
+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
+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.
+
+ (*) CCR.ICC2.C [Carry flag]
+
+ Clear to indicate hardware interrupts are really disabled, set otherwise.
+
+
+What happens is this:
+
+ (1) Normal kernel-mode operation.
+
+ 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.
+
+ (3) The interrupts are disabled (local_irq_disable)
+
+ ICC2.Z is set to 1.
+
+ (4) If interrupts were then re-enabled (local_irq_enable):
+
+ 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).
+
+ (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 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.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.
+
+ (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.
+
+ 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.
+
+(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)).
+
+(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.
diff -uNrp linux-2.6.16-rc2-frv/include/asm-frv/spr-regs.h linux-2.6.16-rc2-frv-int/include/asm-frv/spr-regs.h
--- linux-2.6.16-rc2-frv/include/asm-frv/spr-regs.h 2005-03-02 12:08:45.000000000 +0000
+++ linux-2.6.16-rc2-frv-int/include/asm-frv/spr-regs.h 2006-02-10 13:50:43.000000000 +0000
@@ -98,6 +98,7 @@
#define TBR_TT_TRAP0 (0x80 << 4)
#define TBR_TT_TRAP1 (0x81 << 4)
#define TBR_TT_TRAP2 (0x82 << 4)
+#define TBR_TT_TRAP3 (0x83 << 4)
#define TBR_TT_TRAP126 (0xfe << 4)
#define TBR_TT_BREAK (0xff << 4)
diff -uNrp linux-2.6.16-rc2-frv/include/asm-frv/system.h linux-2.6.16-rc2-frv-int/include/asm-frv/system.h
--- linux-2.6.16-rc2-frv/include/asm-frv/system.h 2005-06-22 13:52:26.000000000 +0100
+++ linux-2.6.16-rc2-frv-int/include/asm-frv/system.h 2006-02-10 16:44:42.000000000 +0000
@@ -40,8 +40,84 @@ do { \
/*
* interrupt flag manipulation
+ * - use virtual interrupt management since touching the PSR is slow
+ * - ICC2.Z: T if interrupts virtually disabled
+ * - ICC2.C: F if interrupts really disabled
+ * - if Z==1 upon interrupt:
+ * - C is set to 0
+ * - interrupts are really disabled
+ * - entry.S returns immediately
+ * - uses TIHI (TRAP if Z==0 && C==0) #2 to really reenable interrupts
+ * - if taken, the trap:
+ * - sets ICC2.C
+ * - enables interrupts
*/
-#define local_irq_disable() \
+#define local_irq_disable() \
+do { \
+ /* set Z flag, but don't change the C flag */ \
+ asm volatile(" andcc gr0,gr0,gr0,icc2 \n" \
+ : \
+ : \
+ : "memory", "icc2" \
+ ); \
+} while(0)
+
+#define local_irq_enable() \
+do { \
+ /* clear Z flag and then test the C flag */ \
+ asm volatile(" oricc gr0,#1,gr0,icc2 \n" \
+ " tihi icc2,gr0,#2 \n" \
+ : \
+ : \
+ : "memory", "icc2" \
+ ); \
+} while(0)
+
+#define local_save_flags(flags) \
+do { \
+ typecheck(unsigned long, flags); \
+ asm volatile("movsg ccr,%0" \
+ : "=r"(flags) \
+ : \
+ : "memory"); \
+ \
+ /* shift ICC2.Z to bit 0 */ \
+ flags >>= 26; \
+ \
+ /* make flags 1 if interrupts disabled, 0 otherwise */ \
+ flags &= 1UL; \
+} while(0)
+
+#define irqs_disabled() \
+ ({unsigned long flags; local_save_flags(flags); flags; })
+
+#define local_irq_save(flags) \
+do { \
+ typecheck(unsigned long, flags); \
+ local_save_flags(flags); \
+ local_irq_disable(); \
+} while(0)
+
+#define local_irq_restore(flags) \
+do { \
+ typecheck(unsigned long, flags); \
+ \
+ /* load the Z flag by turning 1 if disabled into 0 if disabled \
+ * and thus setting the Z flag but not the C flag */ \
+ asm volatile(" xoricc %0,#1,gr0,icc2 \n" \
+ /* then test Z=0 and C=0 */ \
+ " tihi icc2,gr0,#2 \n" \
+ : \
+ : "r"(flags) \
+ : "memory", "icc2" \
+ ); \
+ \
+} while(0)
+
+/*
+ * real interrupt flag manipulation
+ */
+#define __local_irq_disable() \
do { \
unsigned long psr; \
asm volatile(" movsg psr,%0 \n" \
@@ -53,7 +129,7 @@ do { \
: "memory"); \
} while(0)
-#define local_irq_enable() \
+#define __local_irq_enable() \
do { \
unsigned long psr; \
asm volatile(" movsg psr,%0 \n" \
@@ -64,7 +140,7 @@ do { \
: "memory"); \
} while(0)
-#define local_save_flags(flags) \
+#define __local_save_flags(flags) \
do { \
typecheck(unsigned long, flags); \
asm("movsg psr,%0" \
@@ -73,7 +149,7 @@ do { \
: "memory"); \
} while(0)
-#define local_irq_save(flags) \
+#define __local_irq_save(flags) \
do { \
unsigned long npsr; \
typecheck(unsigned long, flags); \
@@ -86,7 +162,7 @@ do { \
: "memory"); \
} while(0)
-#define local_irq_restore(flags) \
+#define __local_irq_restore(flags) \
do { \
typecheck(unsigned long, flags); \
asm volatile(" movgs %0,psr \n" \
@@ -95,7 +171,7 @@ do { \
: "memory"); \
} while(0)
-#define irqs_disabled() \
+#define __irqs_disabled() \
((__get_PSR() & PSR_PIL) >= PSR_PIL_14)
/*