sh: Use a jump call table for debug trap handlers.

This rips out most of the needlessly complicated sh_bios and kgdb
trap handling, and forces it all through a common fast dispatch path.
As more debug traps are inserted, it's important to keep them in sync
for all of the parts, not just SH-3/4.

As the SH-2 parts are unable to do traps in the >= 0x40 range, we
restrict the debug traps to the 0x30-0x3f range on all parts, and
also bump the kgdb breakpoint trap down in to this range (from 0xff
to 0x3c) so it's possible to use for nommu.

Optionally, this table can be padded out to catch spurious traps for
SH-3/4, but we don't do that yet..

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

1 files changed, 43 insertions, 76 deletions

diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S
index fc279aeb73ab..ab4ebb856c2a 100644
--- a/arch/sh/kernel/entry-common.S
+++ b/arch/sh/kernel/entry-common.S
@@ -54,79 +54,24 @@
 #  define resume_kernel         __restore_all
 #endif
 
-#if defined(CONFIG_SH_STANDARD_BIOS) || defined(CONFIG_SH_KGDB)
-! Handle kernel debug if either kgdb (SW) or gdb-stub (FW) is present.
-! If both are configured, handle the debug traps (breakpoints) in SW,
-! but still allow BIOS traps to FW.
-
-        .align  2
-debug_kernel:
-#if defined(CONFIG_SH_STANDARD_BIOS) && defined(CONFIG_SH_KGDB)
-        /* Force BIOS call to FW (debug_trap put TRA in r8) */
-        mov     r8,r0
-        shlr2   r0
-        cmp/eq  #0x3f,r0
-        bt      debug_kernel_fw
-#endif /* CONFIG_SH_STANDARD_BIOS && CONFIG_SH_KGDB */
-
-debug_enter:            
-#if defined(CONFIG_SH_KGDB)
-        /* Jump to kgdb, pass stacked regs as arg */
-debug_kernel_sw:
-        mov.l   3f, r0
-        jmp     @r0
-         mov    r15, r4
-        .align  2
-3:      .long   kgdb_handle_exception
-#endif /* CONFIG_SH_KGDB */
-#ifdef CONFIG_SH_STANDARD_BIOS
-        bra     debug_kernel_fw
-         nop
-#endif
-#endif /* CONFIG_SH_STANDARD_BIOS || CONFIG_SH_KGDB */
-
-        .align  2
-debug_trap:     
-#if defined(CONFIG_SH_STANDARD_BIOS) || defined(CONFIG_SH_KGDB)
-        mov     r8, r0
-        shlr2   r0
-        cmp/eq  #0x3f, r0               ! sh_bios() trap
-        bf      1f
-#ifdef CONFIG_SH_KGDB
-        cmp/eq  #0xff, r0               ! XXX: KGDB trap, fix for SH-2.
-        bf      1f
-#endif
-        mov     #OFF_SR, r0
-        mov.l   @(r0,r15), r0           ! get status register
-        shll    r0
-        shll    r0                      ! kernel space?
-        bt/s    debug_kernel
-1:
-#endif
-         mov.l  @r15, r0                ! Restore R0 value
-        mov.l   1f, r8
-        jmp     @r8
-         nop
 
         .align  2
 ENTRY(exception_error)
         !
 #ifdef CONFIG_TRACE_IRQFLAGS
-        mov.l   3f, r0
+        mov.l   2f, r0
         jsr     @r0
          nop
 #endif
         sti
-        mov.l   2f, r0
+        mov.l   1f, r0
         jmp     @r0
          nop
 
-!
         .align  2
-1:      .long   break_point_trap_software
-2:      .long   do_exception_error
+1:      .long   do_exception_error
 #ifdef CONFIG_TRACE_IRQFLAGS
-3:      .long   trace_hardirqs_on
+2:      .long   trace_hardirqs_on
 #endif
 
         .align  2
@@ -331,16 +276,31 @@ __restore_all:
 1:      .long   restore_all
 
         .align  2
-not_syscall_tra:        
-        bra     debug_trap
-         nop
-
-        .align  2
 syscall_badsys:                 ! Bad syscall number
         mov     #-ENOSYS, r0
         bra     resume_userspace
          mov.l  r0, @(OFF_R0,r15)       ! Return value
-        
+
+/*
+ * The main debug trap handler.
+ *
+ * r8=TRA (not the trap number!)
+ *
+ * Note: This assumes that the trapa value is left in its original
+ * form (without the shlr2 shift) so the calculation for the jump
+ * call table offset remains a simple in place mask.
+ */
+debug_trap:
+        mov     r8, r0
+        and     #(0xf << 2), r0
+        mov.l   1f, r8
+        add     r0, r8
+        mov.l   @r8, r8
+        jmp     @r8
+         nop
+
+        .align  2
+1:      .long   debug_trap_table
 
 /*
  * Syscall interface:
@@ -348,17 +308,19 @@ syscall_badsys:			! Bad syscall number
  *      Syscall #: R3
  *      Arguments #0 to #3: R4--R7
  *      Arguments #4 to #6: R0, R1, R2
- *      TRA: (number of arguments + 0x10) x 4
+ *      TRA: (number of arguments + ABI revision) x 4
  *
  * This code also handles delegating other traps to the BIOS/gdb stub
  * according to:
  *
  * Trap number
- * (TRA>>2)         Purpose
- * --------         -------
- * 0x0-0xf          old syscall ABI
- * 0x10-0x1f        new syscall ABI
- * 0x20-0xff        delegated through debug_trap to BIOS/gdb stub.
+ * (TRA>>2)     Purpose
+ * --------     -------
+ * 0x00-0x0f    original SH-3/4 syscall ABI (not in general use).
+ * 0x10-0x1f    general SH-3/4 syscall ABI.
+ * 0x20-0x2f    syscall ABI for SH-2 parts.
+ * 0x30-0x3f    debug traps used by the kernel.
+ * 0x40-0xff    Not supported by all parts, so left unhandled.
  *
  * Note: When we're first called, the TRA value must be shifted
  * right 2 bits in order to get the value that was used as the "trapa"
@@ -375,17 +337,22 @@ ret_from_fork:
          nop
         .align  2
 1:      .long   schedule_tail
-        !
+
+/*
+ * The poorly named main trapa decode and dispatch routine, for
+ * system calls and debug traps through their respective jump tables.
+ */
 ENTRY(system_call)
 #if !defined(CONFIG_CPU_SH2)
         mov.l   1f, r9
         mov.l   @r9, r8         ! Read from TRA (Trap Address) Register
 #endif
-        !
-        ! Is the trap argument >= 0x20? (TRA will be >= 0x80)
-        mov     #0x7f, r9
+        /*
+         * Check the trap type
+         */
+        mov     #((0x20 << 2) - 1), r9
         cmp/hi  r9, r8
-        bt/s    not_syscall_tra
+        bt/s    debug_trap              ! it's a debug trap..
          mov    #OFF_TRA, r9
         add     r15, r9
         mov.l   r8, @r9                 ! set TRA value to tra