arch/mips/kernel/r2300_switch.S

   1 /*
   2  * r2300_switch.S: R2300 specific task switching code.
   3  *
   4  * Copyright (C) 1994, 1995, 1996, 1999 by Ralf Baechle
   5  * Copyright (C) 1994, 1995, 1996 by Andreas Busse
   6  *
   7  * Multi-cpu abstraction and macros for easier reading:
   8  * Copyright (C) 1996 David S. Miller (davem@davemloft.net)
   9  *
  10  * Further modifications to make this work:
  11  * Copyright (c) 1998-2000 Harald Koerfgen
  12  */
  13 #include <asm/asm.h>
  14 #include <asm/cachectl.h>
  15 #include <asm/fpregdef.h>
  16 #include <asm/mipsregs.h>
  17 #include <asm/asm-offsets.h>
  18 #include <asm/page.h>
  19 #include <asm/regdef.h>
  20 #include <asm/stackframe.h>
  21 #include <asm/thread_info.h>
  22
  23 #include <asm/asmmacro.h>
  24
  25         .set    mips1
  26         .align  5
  27
  28 /*
  29  * Offset to the current process status flags, the first 32 bytes of the
  30  * stack are not used.
  31  */
  32 #define ST_OFF (_THREAD_SIZE - 32 - PT_SIZE + PT_STATUS)
  33
  34 /*
  35  * FPU context is saved iff the process has used it's FPU in the current
  36  * time slice as indicated by TIF_USEDFPU.  In any case, the CU1 bit for user
  37  * space STATUS register should be 0, so that a process *always* starts its
  38  * userland with FPU disabled after each context switch.
  39  *
  40  * FPU will be enabled as soon as the process accesses FPU again, through
  41  * do_cpu() trap.
  42  */
  43
  44 /*
  45  * task_struct *resume(task_struct *prev, task_struct *next,
  46  *                     struct thread_info *next_ti) )
  47  */
  48 LEAF(resume)
  49         mfc0    t1, CP0_STATUS
  50         sw      t1, THREAD_STATUS(a0)
  51         cpu_save_nonscratch a0
  52         sw      ra, THREAD_REG31(a0)
  53
  54         /*
  55          * check if we need to save FPU registers
  56          */
  57         lw      t3, TASK_THREAD_INFO(a0)
  58         lw      t0, TI_FLAGS(t3)
  59         li      t1, _TIF_USEDFPU
  60         and     t2, t0, t1
  61         beqz    t2, 1f
  62         nor     t1, zero, t1
  63
  64         and     t0, t0, t1
  65         sw      t0, TI_FLAGS(t3)
  66
  67         /*
  68          * clear saved user stack CU1 bit
  69          */
  70         lw      t0, ST_OFF(t3)
  71         li      t1, ~ST0_CU1
  72         and     t0, t0, t1
  73         sw      t0, ST_OFF(t3)
  74
  75         fpu_save_single a0, t0                  # clobbers t0
  76
  77 1:
  78         /*
  79          * The order of restoring the registers takes care of the race
  80          * updating $28, $29 and kernelsp without disabling ints.
  81          */
  82         move    $28, a2
  83         cpu_restore_nonscratch a1
  84
  85         addiu   t1, $28, _THREAD_SIZE - 32
  86         sw      t1, kernelsp
  87
  88         mfc0    t1, CP0_STATUS          /* Do we really need this? */
  89         li      a3, 0xff01
  90         and     t1, a3
  91         lw      a2, THREAD_STATUS(a1)
  92         nor     a3, $0, a3
  93         and     a2, a3
  94         or      a2, t1
  95         mtc0    a2, CP0_STATUS
  96         move    v0, a0
  97         jr      ra
  98         END(resume)
  99
 100 /*
 101  * Save a thread's fp context.
 102  */
 103 LEAF(_save_fp)
 104         fpu_save_single a0, t1                  # clobbers t1
 105         jr      ra
 106         END(_save_fp)
 107
 108 /*
 109  * Restore a thread's fp context.
 110  */
 111 LEAF(_restore_fp)
 112         fpu_restore_single a0, t1               # clobbers t1
 113         jr      ra
 114         END(_restore_fp)
 115
 116 /*
 117  * Load the FPU with signalling NANS.  This bit pattern we're using has
 118  * the property that no matter whether considered as single or as double
 119  * precision represents signaling NANS.
 120  *
 121  * We initialize fcr31 to rounding to nearest, no exceptions.
 122  */
 123
 124 #define FPU_DEFAULT  0x00000000
 125
 126 LEAF(_init_fpu)
 127         mfc0    t0, CP0_STATUS
 128         li      t1, ST0_CU1
 129         or      t0, t1
 130         mtc0    t0, CP0_STATUS
 131
 132         li      t1, FPU_DEFAULT
 133         ctc1    t1, fcr31
 134
 135         li      t0, -1
 136
 137         mtc1    t0, $f0
 138         mtc1    t0, $f1
 139         mtc1    t0, $f2
 140         mtc1    t0, $f3
 141         mtc1    t0, $f4
 142         mtc1    t0, $f5
 143         mtc1    t0, $f6
 144         mtc1    t0, $f7
 145         mtc1    t0, $f8
 146         mtc1    t0, $f9
 147         mtc1    t0, $f10
 148         mtc1    t0, $f11
 149         mtc1    t0, $f12
 150         mtc1    t0, $f13
 151         mtc1    t0, $f14
 152         mtc1    t0, $f15
 153         mtc1    t0, $f16
 154         mtc1    t0, $f17
 155         mtc1    t0, $f18
 156         mtc1    t0, $f19
 157         mtc1    t0, $f20
 158         mtc1    t0, $f21
 159         mtc1    t0, $f22
 160         mtc1    t0, $f23
 161         mtc1    t0, $f24
 162         mtc1    t0, $f25
 163         mtc1    t0, $f26
 164         mtc1    t0, $f27
 165         mtc1    t0, $f28
 166         mtc1    t0, $f29
 167         mtc1    t0, $f30
 168         mtc1    t0, $f31
 169         jr      ra
 170         END(_init_fpu)