sh: shared register saving code for sh3/sh4/sh4a

This patch reworks the sh3/sh4/sh4a register saving code in
the following ways:
 - break out prepare_stack_save_dsp() from handle_exception()
 - break out save_regs() from handle_exception()
 - the register saving order is unchanged
 - align new functions to fit in cache lines
 - separate exception code from interrupt code
 - keep main code flow in a single cache line per exception vector
 - use bsr/rts for regular functions (save pr first)
 - keep data in one shared cache line (exception_data)
 - document the functions
 - tie in the hp6xx code

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

2 files changed, 155 insertions, 149 deletions

diff --git a/arch/sh/boards/mach-hp6xx/pm_wakeup.S b/arch/sh/boards/mach-hp6xx/pm_wakeup.S
index 44b648cf6f23..4f18d44e0541 100644
--- a/arch/sh/boards/mach-hp6xx/pm_wakeup.S
+++ b/arch/sh/boards/mach-hp6xx/pm_wakeup.S
@@ -10,47 +10,32 @@
 #include <linux/linkage.h>
 #include <cpu/mmu_context.h>
 
-#define k0      r0
-#define k1      r1
-#define k2      r2
-#define k3      r3
-#define k4      r4
-
 /*
  * Kernel mode register usage:
  *      k0      scratch
  *      k1      scratch
- *      k2      scratch (Exception code)
- *      k3      scratch (Return address)
- *      k4      scratch
- *      k5      reserved
- *      k6      Global Interrupt Mask (0--15 << 4)
- *      k7      CURRENT_THREAD_INFO (pointer to current thread info)
+ * For more details, please have a look at entry.S
  */
 
+#define k0      r0
+#define k1      r1
+
 ENTRY(wakeup_start)
 ! clear STBY bit
-        mov     #-126, k2
+        mov     #-126, k1
         and     #127, k0
-        mov.b   k0, @k2
+        mov.b   k0, @k1
 ! enable refresh
         mov.l   5f, k1
         mov.w   6f, k0
         mov.w   k0, @k1
 ! jump to handler
-        mov.l   2f, k2
-        mov.l   3f, k3
-        mov.l   @k2, k2
-
         mov.l   4f, k1
         jmp     @k1
-        nop
+         nop
 
         .align  2
-1:      .long   EXPEVT
-2:      .long   INTEVT
-3:      .long   ret_from_irq
-4:      .long   handle_exception
+4:      .long   handle_interrupt
 5:      .long   0xffffff68
 6:      .word   0x0524
 
diff --git a/arch/sh/kernel/cpu/sh3/entry.S b/arch/sh/kernel/cpu/sh3/entry.S
index b4106d0c68ec..f3db143e70b2 100644
--- a/arch/sh/kernel/cpu/sh3/entry.S
+++ b/arch/sh/kernel/cpu/sh3/entry.S
@@ -16,6 +16,7 @@
 #include <asm/unistd.h>
 #include <cpu/mmu_context.h>
 #include <asm/page.h>
+#include <asm/cache.h>
 
 ! NOTE:
 ! GNU as (as of 2.9.1) changes bf/s into bt/s and bra, when the address
@@ -294,7 +295,7 @@ skip_restore:
         mov     #0xf0, k1
         extu.b  k1, k1
         not     k1, k1
-        and     k1, k2                  ! Mask orignal SR value
+        and     k1, k2                  ! Mask original SR value
         !
         mov     k3, k0                  ! Calculate IMASK-bits
         shlr2   k0
@@ -336,81 +337,53 @@ skip_restore:
 ENTRY(vbr_base)
         .long   0
 !
+! 0x100: General exception vector
+!
         .balign         256,0,256
 general_exception:
-        mov.l   1f, k2
-        mov.l   2f, k3
-#ifdef CONFIG_CPU_SUBTYPE_SHX3
-        mov.l   @k2, k2
+#ifndef CONFIG_CPU_SUBTYPE_SHX3
+        bra     handle_exception
+         sts    pr, k3          ! save original pr value in k3
+#else
+        mov.l   1f, k4
+        mov.l   @k4, k4
 
         ! Is EXPEVT larger than 0x800?
         mov     #0x8, k0
         shll8   k0
-        cmp/hs  k0, k2
+        cmp/hs  k0, k4
         bf      0f
 
         ! then add 0x580 (k2 is 0xd80 or 0xda0)
         mov     #0x58, k0
         shll2   k0
         shll2   k0
-        add     k0, k2
+        add     k0, k4
 0:
-        bra     handle_exception
+        ! Setup stack and save DSP context (k0 contains original r15 on return)
+        bsr     prepare_stack_save_dsp
          nop
-#else
-        bra     handle_exception
-         mov.l  @k2, k2
-#endif
-        .align  2
-1:      .long   EXPEVT
-2:      .long   ret_from_exception
-!
-!
 
-        .balign         1024,0,1024
-tlb_miss:
-        mov.l   1f, k2
-        mov.l   4f, k3
-        bra     handle_exception
-         mov.l  @k2, k2
-!
-        .balign         512,0,512
-interrupt:
-        mov.l   3f, k3
-#if defined(CONFIG_KGDB)
-        mov.l   2f, k2
-        ! Debounce (filter nested NMI)
-        mov.l   @k2, k0
-        mov.l   5f, k1
-        cmp/eq  k1, k0
-        bf      0f
-        mov.l   6f, k1
-        tas.b   @k1
-        bt      0f
-        rte
+        ! Save registers / Switch to bank 0
+        bsr     save_regs       ! needs original pr value in k3
+         mov.l  k4, k2          ! keep vector in k2
+
+        bra     handle_exception_special
          nop
-        .align  2
-2:      .long   INTEVT
-5:      .long   NMI_VEC
-6:      .long   in_nmi
-0:
-#endif /* defined(CONFIG_KGDB) */
-        bra     handle_exception
-         mov    #-1, k2         ! interrupt exception marker
 
         .align  2
 1:      .long   EXPEVT
-3:      .long   ret_from_irq
-4:      .long   ret_from_exception
+#endif
 
-!
-!
-        .align  2
-ENTRY(handle_exception)
-        ! Using k0, k1 for scratch registers (r0_bank1, r1_bank),
-        ! save all registers onto stack.
-        !
+! prepare_stack_save_dsp()
+! - roll back gRB
+! - switch to kernel stack
+! - save DSP
+! k0 returns original sp (after roll back)
+! k1 trashed
+! k2 trashed
 
+prepare_stack_save_dsp:
 #ifdef CONFIG_GUSA
         ! Check for roll back gRB (User and Kernel)
         mov     r15, k0
@@ -430,7 +403,7 @@ ENTRY(handle_exception)
 2:      mov     k1, r15         ! SP = r1
 1:
 #endif
-
+        ! Switch to kernel stack if needed
         stc     ssr, k0         ! Is it from kernel space?
         shll    k0              ! Check MD bit (bit30) by shifting it into...
         shll    k0              !       ...the T bit
@@ -443,18 +416,17 @@ ENTRY(handle_exception)
         add     current, k1
         mov     k1, r15         ! change to kernel stack
         !
-1:      mov.l   2f, k1
-        !
+1:
 #ifdef CONFIG_SH_DSP
-        mov.l   r2, @-r15               ! Save r2, we need another reg
-        stc     sr, k4
-        mov.l   1f, r2
-        tst     r2, k4                  ! Check if in DSP mode
-        mov.l   @r15+, r2               ! Restore r2 now
+        ! Save DSP context if needed
+        stc     sr, k1
+        mov     #0x10, k2
+        shll8   k2                      ! DSP=1 (0x00001000)
+        tst     k2, k1                  ! Check if in DSP mode (passed in k2)
         bt/s    skip_save
-         mov    #0, k4                  ! Set marker for no stack frame
+         mov    #0, k1                  ! Set marker for no stack frame
 
-        mov     r2, k4                  ! Backup r2 (in k4) for later
+        mov     k2, k1                  ! Save has-frame marker
 
         ! Save DSP registers on stack
         stc.l   mod, @-r15
@@ -473,35 +445,73 @@ ENTRY(handle_exception)
         ! as we're not at all interested in supporting ancient toolchains at
         ! this point. -- PFM.
 
-        mov     r15, r2
+        mov     r15, k2
         .word   0xf653                  ! movs.l        a1, @-r2
         .word   0xf6f3                  ! movs.l        a0g, @-r2
         .word   0xf6d3                  ! movs.l        a1g, @-r2
         .word   0xf6c3                  ! movs.l        m0, @-r2
         .word   0xf6e3                  ! movs.l        m1, @-r2
-        mov     r2, r15
+        mov     k2, r15
 
-        mov     k4, r2                  ! Restore r2
-        mov.l   1f, k4                  ! Force DSP stack frame
 skip_save:
-        mov.l   k4, @-r15               ! Push DSP mode marker onto stack
+        mov.l   k1, @-r15               ! Push DSP mode marker onto stack
 #endif
-        ! Save the user registers on the stack.
-        mov.l   k2, @-r15       ! EXPEVT
+        rts
+         nop
+!
+! 0x400: Instruction and Data TLB miss exception vector
+!
+        .balign         1024,0,1024
+tlb_miss:
+        sts     pr, k3          ! save original pr value in k3
 
-        mov     #-1, k4
-        mov.l   k4, @-r15       ! set TRA (default: -1)
-        !
+handle_exception:
+        ! Setup stack and save DSP context (k0 contains original r15 on return)
+        bsr     prepare_stack_save_dsp
+         nop
+
+        ! Save registers / Switch to bank 0
+        mov.l   5f, k2          ! vector register address
+        bsr     save_regs       ! needs original pr value in k3
+         mov.l  @k2, k2         ! read out vector and keep in k2
+
+handle_exception_special:
+        ! Setup return address and jump to exception handler
+        mov.l   7f, r9          ! fetch return address
+        stc     r2_bank, r0     ! k2 (vector)
+        mov.l   6f, r10
+        shlr2   r0
+        shlr    r0
+        mov.l   @(r0, r10), r10
+        jmp     @r10
+         lds    r9, pr          ! put return address in pr
+
+        .align  L1_CACHE_SHIFT
+
+! save_regs()
+! - save vector, default tra, macl, mach, gbr, ssr, pr* and spc on the stack
+! - save r15*, r14, r13, r12, r11, r10, r9, r8 on the stack
+! - switch bank
+! - save r7, r6, r5, r4, r3, r2, r1, r0 on the stack
+! k0 contains original stack pointer*
+! k1 trashed
+! k2 passes vector (EXPEVT)
+! k3 passes original pr*
+! k4 trashed
+! BL=1 on entry, on exit BL=0.
+
+save_regs:
+        mov     #-1, r1
+        mov.l   k2, @-r15       ! vector in k2
+        mov.l   k1, @-r15       ! set TRA (default: -1)
         sts.l   macl, @-r15
         sts.l   mach, @-r15
         stc.l   gbr, @-r15
         stc.l   ssr, @-r15
-        sts.l   pr, @-r15
+        mov.l   k3, @-r15       ! original pr in k3
         stc.l   spc, @-r15
-        !
-        lds     k3, pr          ! Set the return address to pr
-        !
-        mov.l   k0, @-r15       ! save orignal stack
+
+        mov.l   k0, @-r15       ! original stack pointer in k0
         mov.l   r14, @-r15
         mov.l   r13, @-r15
         mov.l   r12, @-r15
@@ -509,13 +519,15 @@ skip_save:
         mov.l   r10, @-r15
         mov.l   r9, @-r15
         mov.l   r8, @-r15
-        !
-        stc     sr, r8          ! Back to normal register bank, and
-        or      k1, r8          ! Block all interrupts
-        mov.l   3f, k1
-        and     k1, r8          ! ...
-        ldc     r8, sr          ! ...changed here.
-        !
+
+        mov.l   0f, k3          ! SR bits to set in k3
+        mov.l   1f, k4          ! SR bits to clear in k4
+
+        stc     sr, r8
+        or      k3, r8
+        and     k4, r8
+        ldc     r8, sr
+
         mov.l   r7, @-r15
         mov.l   r6, @-r15
         mov.l   r5, @-r15
@@ -523,52 +535,61 @@ skip_save:
         mov.l   r3, @-r15
         mov.l   r2, @-r15
         mov.l   r1, @-r15
-        mov.l   r0, @-r15
-
-        /*
-         * 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
-        add     r8, r9
-        mov.l   @r9, r9
-        jmp     @r9
-         nop
         rts
-         nop
+         mov.l  r0, @-r15
 
+!
+! 0x600: Interrupt / NMI vector
+!
+        .balign         512,0,512
+ENTRY(handle_interrupt)
+#if defined(CONFIG_KGDB)
+        mov.l   2f, k2
+        ! Debounce (filter nested NMI)
+        mov.l   @k2, k0
+        mov.l   9f, k1
+        cmp/eq  k1, k0
+        bf      11f
+        mov.l   10f, k1
+        tas.b   @k1
+        bt      11f
+        rte
+         nop
         .align  2
-1:      .long   0x00001000      ! DSP=1
-2:      .long   0x000080f0      ! FD=1, IMASK=15
-3:      .long   0xcfffffff      ! RB=0, BL=0
-4:      .long   exception_handling_table
+9:      .long   NMI_VEC
+10:     .long   in_nmi
+11:
+#endif /* defined(CONFIG_KGDB) */
+        sts     pr, k3          ! save original pr value in k3
 
-interrupt_exception:
-        mov.l   1f, r9
-        mov.l   2f, r4
-        mov.l   @r4, r4
-        jmp     @r9
-         mov    r15, r5
-        rts
+        ! Setup stack and save DSP context (k0 contains original r15 on return)
+        bsr     prepare_stack_save_dsp
          nop
 
-        .align 2
-1:      .long   do_IRQ
-2:      .long   INTEVT
+        ! Save registers / Switch to bank 0
+        bsr     save_regs       ! needs original pr value in k3
+         mov    #-1, k2         ! default vector kept in k2
+
+        ! Setup return address and jump to do_IRQ
+        mov.l   4f, r9          ! fetch return address
+        lds     r9, pr          ! put return address in pr
+        mov.l   2f, r4
+        mov.l   3f, r9
+        mov.l   @r4, r4         ! pass INTEVT vector as arg0
+        jmp     @r9
+         mov    r15, r5         ! pass saved registers as arg1
 
-        .align  2
 ENTRY(exception_none)
         rts
          nop
+
+        .align  L1_CACHE_SHIFT
+exception_data:
+0:      .long   0x000080f0      ! FD=1, IMASK=15
+1:      .long   0xcfffffff      ! RB=0, BL=0
+2:      .long   INTEVT
+3:      .long   do_IRQ
+4:      .long   ret_from_irq
+5:      .long   EXPEVT
+6:      .long   exception_handling_table
+7:      .long   ret_from_exception