[PATCH] FRV: Use virtual interrupt disablement

Make 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@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

6 files changed, 172 insertions, 55 deletions

diff --git a/arch/frv/Makefile b/arch/frv/Makefile
index 90c0fb8d9dc3..d163747d17c0 100644
--- a/arch/frv/Makefile
+++ b/arch/frv/Makefile
@@ -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 --git a/arch/frv/kernel/break.S b/arch/frv/kernel/break.S
index 33233dc23e29..687c48d62dde 100644
--- a/arch/frv/kernel/break.S
+++ b/arch/frv/kernel/break.S
@@ -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 --git a/arch/frv/kernel/entry-table.S b/arch/frv/kernel/entry-table.S
index 9b9243e2103c..81568acea9cd 100644
--- a/arch/frv/kernel/entry-table.S
+++ b/arch/frv/kernel/entry-table.S
@@ -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 --git a/arch/frv/kernel/entry.S b/arch/frv/kernel/entry.S
index c69d499d28cf..1d21c8d34d8a 100644
--- a/arch/frv/kernel/entry.S
+++ b/arch/frv/kernel/entry.S
@@ -141,7 +141,10 @@ __entry_uspace_external_interrupt_reentry:
 
         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_reentry:
         .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_reentry:
         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_reentry:
 
         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_reentry:
 
         .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_reentry:
 
         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 --git a/arch/frv/kernel/head.S b/arch/frv/kernel/head.S
index c73b4fe9f6ca..29a5265489b7 100644
--- a/arch/frv/kernel/head.S
+++ b/arch/frv/kernel/head.S
@@ -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 --git a/arch/frv/kernel/irq.c b/arch/frv/kernel/irq.c
index 59580c59c62c..27ab4c30aac6 100644
--- a/arch/frv/kernel/irq.c
+++ b/arch/frv/kernel/irq.c
@@ -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() */