sh: interrupt exception handling rework

Kill off interrupt_table for all of the CPU subtypes, we now
default in to stepping in to do_IRQ() for _all_ IRQ exceptions
and counting the spurious ones, rather than simply flipping on
the ones we cared about. This and enabling the IRQ by default
automatically has already uncovered a couple of bugs and IRQs
that weren't being caught, as well as some that are being
generated far too often (SCI Tx Data Empty, for example).

The general rationale is to use a marker for interrupt exceptions,
test for it in the handle_exception() path, and skip out to
do_IRQ() if it's found. Everything else follows the same behaviour
of finding the cached EXPEVT value in r2/r2_bank, we just rip out
the INTEVT read from entry.S entirely (except for in the kGDB NMI
case, which is another matter).

Note that while this changes the do_IRQ() semantics regarding r4
handling, they were fundamentally broken anyways (relying entirely
on r2_bank for the cached code). With this, we do the INTEVT read
from do_IRQ() itself (in the CONFIG_CPU_HAS_INTEVT case), or fall
back on r4 for the muxed IRQ number, which should also be closer
to what SH-2 and SH-2A want anyways.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 33 insertions, 10 deletions

diff --git a/arch/sh/kernel/entry.S b/arch/sh/kernel/entry.S
index 97c571fbcdf1..39aaefb2d83f 100644
--- a/arch/sh/kernel/entry.S
+++ b/arch/sh/kernel/entry.S
@@ -1,9 +1,8 @@
-/* $Id: entry.S,v 1.37 2004/06/11 13:02:46 doyu Exp $
- *
+/*
  *  linux/arch/sh/entry.S
  *
  *  Copyright (C) 1999, 2000, 2002  Niibe Yutaka
- *  Copyright (C) 2003  Paul Mundt
+ *  Copyright (C) 2003 - 2006  Paul Mundt
  *
  * This file is subject to the terms and conditions of the GNU General Public
  * License.  See the file "COPYING" in the main directory of this archive
@@ -78,7 +77,6 @@ OFF_TRA	=  (16*4+6*4)
 #define k3      r3
 #define k4      r4
 
-#define k_ex_code       r2_bank /* r2_bank1 */
 #define g_imask         r6      /* r6_bank1 */
 #define k_g_imask       r6_bank /* r6_bank1 */
 #define current         r7      /* r7_bank1 */
@@ -691,7 +689,7 @@ interrupt:
 0:
 #endif /* defined(CONFIG_KGDB_NMI) */
         bra     handle_exception
-         mov.l  @k2, k2
+         mov    #-1, k2         ! interrupt exception marker
 
         .align  2
 1:      .long   EXPEVT
@@ -717,8 +715,7 @@ ENTRY(handle_exception)
         add     current, k1
         mov     k1, r15         ! change to kernel stack
         !
-1:      mov     #-1, k4
-        mov.l   2f, k1
+1:      mov.l   2f, k1
         !
 #ifdef CONFIG_SH_DSP
         mov.l   r2, @-r15               ! Save r2, we need another reg
@@ -763,6 +760,8 @@ skip_save:
 #endif
         ! Save the user registers on the stack.
         mov.l   k2, @-r15       ! EXPEVT
+
+        mov     #-1, k4
         mov.l   k4, @-r15       ! set TRA (default: -1)
         !
         sts.l   macl, @-r15
@@ -797,8 +796,21 @@ skip_save:
         mov.l   r2, @-r15
         mov.l   r1, @-r15
         mov.l   r0, @-r15
-        ! Then, dispatch to the handler, according to the exception code.
-        stc     k_ex_code, r8
+
+        /*
+         * This gets a bit tricky.. in the INTEVT case we don't want to use
+         * the VBR offset as a destination in the jump call table, since all
+         * of the destinations are the same. In this case, (interrupt) sets
+         * a marker in r2 (now r2_bank since SR.RB changed), which we check
+         * to determine the exception type. For all other exceptions, we
+         * forcibly read EXPEVT from memory and fix up the jump address, in
+         * the interrupt exception case we jump to do_IRQ() and defer the
+         * INTEVT read until there. As a bonus, we can also clean up the SR.RB
+         * checks that do_IRQ() was doing..
+         */
+        stc     r2_bank, r8
+        cmp/pz  r8
+        bf      interrupt_exception
         shlr2   r8
         shlr    r8
         mov.l   4f, r9
@@ -806,6 +818,8 @@ skip_save:
         mov.l   @r9, r9
         jmp     @r9
          nop
+        rts
+         nop
 
         .align  2
 1:      .long   0x00001000      ! DSP=1
@@ -813,8 +827,17 @@ skip_save:
 3:      .long   0xcfffffff      ! RB=0, BL=0
 4:      .long   exception_handling_table
 
+interrupt_exception:
+        mov.l   1f, r9
+        jmp     @r9
+         nop
+        rts
+         nop
+
+        .align 2
+1:      .long   do_IRQ
+
         .align  2
 ENTRY(exception_none)
         rts
          nop
-