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m68k: Simplify low level interrupt handling code

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The low level interrupt entry code of m68k contains the following:

    add_preempt_count(HARDIRQ_OFFSET);

    do_IRQ();
	irq_enter();
	    add_preempt_count(HARDIRQ_OFFSET);
	handle_interrupt();    
	irq_exit();    
	    sub_preempt_count(HARDIRQ_OFFSET);
	    if (in_interrupt())
       	       return; <---- On m68k always taken!
	    if (local_softirq_pending())
       	       do_softirq();

    sub_preempt_count(HARDIRQ_OFFSET);
    if (in_hardirq())
       return;
    if (status_on_stack_has_interrupt_priority_mask > 0)
       return;
    if (local_softirq_pending())
       do_softirq();

    ret_from_exception:
	if (interrupted_context_is_kernel)
	   return:
	....

I tried to find a proper explanation for this, but the changelog is
sparse and there are no mails explaining it further. But obviously
this relates to the interrupt priority levels of the m68k and tries to
be extra clever with nested interrupts. Though this cleverness just
adds code bloat to the interrupt hotpath.

For the common case of non nested interrupts the code runs through two
extra conditionals to the only important one, which checks whether the
return is to kernel or user space.

For the nested case the checks for in_hardirq() and the priority mask
value on stack catch only the case where the nested interrupt happens
inside the hard irq context of the first interrupt. If the nested
interrupt happens while the first interrupt handles soft interrupts,
then these extra checks buy nothing. The nested interrupt will fall
through to the final kernel/user space return check at
ret_from_exception.

Changing the code flow in the following way:

    do_IRQ();
	irq_enter();
	    add_preempt_count(HARDIRQ_OFFSET);
	handle_interrupt();    
	irq_exit();    
	    sub_preempt_count(HARDIRQ_OFFSET);
	    if (in_interrupt())
       	       return;
	    if (local_softirq_pending())
       	       do_softirq();

    ret_from_exception:
	if (interrupted_context_is_kernel)
	   return:

makes the region protected by the hardirq count slightly smaller and
the softirq handling is invoked with a minimal deeper stack. But
otherwise it's completely functional equivalent and saves 104 bytes of
text in arch/m68k/kernel/entry.o.

This modification allows us further to get rid of the limitations
which m68k puts on the preempt_count layout, so we can make the
preempt count bits completely generic.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Schmitz <schmitz@biophys.uni-duesseldorf.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Linux/m68k <linux-m68k@vger.kernel.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1311112052360.30673@ionos.tec.linutronix.de
This commit is contained in:
Thomas Gleixner 2013-11-11 21:01:03 +01:00
parent b39898cd40
commit 09f90f6685
4 changed files with 15 additions and 88 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
arch/m68k/kernel/entry.S
View File

@ -45,7 +45,7 @@
.globl system_call, buserr, trap, resume
.globl sys_call_table
.globl __sys_fork, __sys_clone, __sys_vfork
.globl ret_from_interrupt, bad_interrupt
.globl bad_interrupt
.globl auto_irqhandler_fixup
.globl user_irqvec_fixup
@ -275,8 +275,6 @@ do_delayed_trace:
ENTRY(auto_inthandler)
SAVE_ALL_INT
GET_CURRENT(%d0)
movel %d0,%a1
addqb #1,%a1@(TINFO_PREEMPT+1)
| put exception # in d0
bfextu %sp@(PT_OFF_FORMATVEC){#4,#10},%d0
subw #VEC_SPUR,%d0
@ -286,32 +284,13 @@ ENTRY(auto_inthandler)
auto_irqhandler_fixup = . + 2
jsr do_IRQ | process the IRQ
addql #8,%sp | pop parameters off stack
ret_from_interrupt:
movel %curptr@(TASK_STACK),%a1
subqb #1,%a1@(TINFO_PREEMPT+1)
jeq ret_from_last_interrupt
2: RESTORE_ALL
ALIGN
ret_from_last_interrupt:
moveq #(~ALLOWINT>>8)&0xff,%d0
andb %sp@(PT_OFF_SR),%d0
jne 2b
/* check if we need to do software interrupts */
tstl irq_stat+CPUSTAT_SOFTIRQ_PENDING
jeq .Lret_from_exception
pea ret_from_exception
jra do_softirq
jra ret_from_exception
/* Handler for user defined interrupt vectors */
ENTRY(user_inthandler)
SAVE_ALL_INT
GET_CURRENT(%d0)
movel %d0,%a1
addqb #1,%a1@(TINFO_PREEMPT+1)
| put exception # in d0
bfextu %sp@(PT_OFF_FORMATVEC){#4,#10},%d0
user_irqvec_fixup = . + 2
@ -321,29 +300,18 @@ user_irqvec_fixup = . + 2
movel %d0,%sp@- | put vector # on stack
jsr do_IRQ | process the IRQ
addql #8,%sp | pop parameters off stack
movel %curptr@(TASK_STACK),%a1
subqb #1,%a1@(TINFO_PREEMPT+1)
jeq ret_from_last_interrupt
RESTORE_ALL
jra ret_from_exception
/* Handler for uninitialized and spurious interrupts */
ENTRY(bad_inthandler)
SAVE_ALL_INT
GET_CURRENT(%d0)
movel %d0,%a1
addqb #1,%a1@(TINFO_PREEMPT+1)
movel %sp,%sp@-
jsr handle_badint
addql #4,%sp
movel %curptr@(TASK_STACK),%a1
subqb #1,%a1@(TINFO_PREEMPT+1)
jeq ret_from_last_interrupt
RESTORE_ALL
jra ret_from_exception
resume:
/*

6
arch/m68k/kernel/ints.c
View File

@ -58,12 +58,6 @@ void __init init_IRQ(void)
{
int i;
/* assembly irq entry code relies on this... */
if (HARDIRQ_MASK != 0x00ff0000) {
extern void hardirq_mask_is_broken(void);
hardirq_mask_is_broken();
}
for (i = IRQ_AUTO_1; i <= IRQ_AUTO_7; i++)
irq_set_chip_and_handler(i, &auto_irq_chip, handle_simple_irq);

33
arch/m68k/platform/68000/entry.S
View File

@ -27,7 +27,6 @@
.globl ret_from_exception
.globl ret_from_signal
.globl sys_call_table
.globl ret_from_interrupt
.globl bad_interrupt
.globl inthandler1
.globl inthandler2
@ -137,7 +136,7 @@ inthandler1:
movel #65,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
bra ret_from_exception
inthandler2:
SAVE_ALL_INT
@ -148,7 +147,7 @@ inthandler2:
movel #66,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
bra ret_from_exception
inthandler3:
SAVE_ALL_INT
@ -159,7 +158,7 @@ inthandler3:
movel #67,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
bra ret_from_exception
inthandler4:
SAVE_ALL_INT
@ -170,7 +169,7 @@ inthandler4:
movel #68,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
bra ret_from_exception
inthandler5:
SAVE_ALL_INT
@ -181,7 +180,7 @@ inthandler5:
movel #69,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
bra ret_from_exception
inthandler6:
SAVE_ALL_INT
@ -192,7 +191,7 @@ inthandler6:
movel #70,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
bra ret_from_exception
inthandler7:
SAVE_ALL_INT
@ -203,7 +202,7 @@ inthandler7:
movel #71,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
bra ret_from_exception
inthandler:
SAVE_ALL_INT
@ -214,23 +213,7 @@ inthandler:
movel %d0,%sp@- /* put vector # on stack*/
jbsr process_int /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
ret_from_interrupt:
jeq 1f
2:
RESTORE_ALL
1:
moveb %sp@(PT_OFF_SR), %d0
and #7, %d0
jhi 2b
/* check if we need to do software interrupts */
jeq ret_from_exception
pea ret_from_exception
jra do_softirq
bra ret_from_exception
/*
* Handler for uninitialized and spurious interrupts.

24
arch/m68k/platform/68360/entry.S
View File

@ -29,7 +29,6 @@
.globl ret_from_exception
.globl ret_from_signal
.globl sys_call_table
.globl ret_from_interrupt
.globl bad_interrupt
.globl inthandler
@ -132,26 +131,9 @@ inthandler:
movel %sp,%sp@-
movel %d0,%sp@- /* put vector # on stack*/
jbsr do_IRQ /* process the IRQ*/
3: addql #8,%sp /* pop parameters off stack*/
bra ret_from_interrupt
ret_from_interrupt:
jeq 1f
2:
RESTORE_ALL
1:
moveb %sp@(PT_OFF_SR), %d0
and #7, %d0
jhi 2b
/* check if we need to do software interrupts */
movel irq_stat+CPUSTAT_SOFTIRQ_PENDING,%d0
jeq ret_from_exception
pea ret_from_exception
jra do_softirq
jbsr do_IRQ /* process the IRQ */
addql #8,%sp /* pop parameters off stack*/
jra ret_from_exception
/*
* Handler for uninitialized and spurious interrupts.