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/*
 * r2300_switch.S: R2300 specific task switching code.
 *
 * Copyright (C) 1994, 1995, 1996, 1999 by Ralf Baechle
 * Copyright (C) 1994, 1995, 1996 by Andreas Busse
 *
 * Multi-cpu abstraction and macros for easier reading:
 * Copyright (C) 1996 David S. Miller (dm@engr.sgi.com)
 *
 * Further modifications to make this work:
 * Copyright (c) 1998-2000 Harald Koerfgen
 */
#include <linux/config.h>
#include <asm/asm.h>
#include <asm/cachectl.h>
#include <asm/current.h>
#include <asm/fpregdef.h>
#include <asm/mipsregs.h>
#include <asm/offset.h>
#include <asm/page.h>
#include <asm/pgtable-bits.h>
#include <asm/processor.h>
#include <asm/regdef.h>
#include <asm/stackframe.h>

#include <asm/asmmacro.h>

        .set    mips1
        .align  5

#define PF_USEDFPU      0x00100000      /* task used FPU this quantum (SMP) */
#define ST_OFF (KERNEL_STACK_SIZE - 32 - PT_SIZE + PT_STATUS)

/*
 * [jsun] FPU context is saved if and only if the process has used FPU in 
 * the current run (PF_USEDFPU).  In any case, the CU1 bit for user space 
 * STATUS register should be 0, so that a process *always* starts its 
 * userland with FPU disabled after each context switch.
 *
 * FPU will be enabled as soon as the process accesses FPU again, through
 * do_cpu() trap.
 */

/*
 * task_struct *resume(task_struct *prev,
 *                     task_struct *next)
 */
LEAF(resume)
#ifndef CONFIG_CPU_HAS_LLSC
        sw      zero, ll_bit
#endif
        mfc0    t1, CP0_STATUS
        sw      t1, THREAD_STATUS(a0)
        CPU_SAVE_NONSCRATCH(a0)
        sw      ra, THREAD_REG31(a0)

        /* 
         * check if we need to save FPU registers
         */
        lw      t0, TASK_FLAGS(a0)
        li      t1, PF_USEDFPU
        and     t2, t0, t1
        beqz    t2, 1f
        nor     t1, zero, t1

        /*
         * clear PF_USEDFPU bit in task flags
         */
        and     t0, t0, t1
        sw      t0, TASK_FLAGS(a0)

        /*
         * clear user-saved stack CU1 bit
         */
        lw      t0, ST_OFF(a0)
        li      t1, ~ST0_CU1
        and     t0, t0, t1
        sw      t0, ST_OFF(a0)

        FPU_SAVE_SINGLE(a0, t0)                 # clobbers t0

1:
        /*
         * The order of restoring the registers takes care of the race
         * updating $28, $29 and kernelsp without disabling ints.
         */
        move    $28, a1
        CPU_RESTORE_NONSCRATCH($28)
        addiu   t0, $28, KERNEL_STACK_SIZE-32
        sw      t0, kernelsp
        mfc0    t1, CP0_STATUS          /* Do we really need this? */
        li      a3, 0xff00
        and     t1, a3
        lw      a2, THREAD_STATUS($28)
        nor     a3, $0, a3
        and     a2, a3
        or      a2, t1
        mtc0    a2, CP0_STATUS
        .set    noreorder
        jr      ra
         move   v0, a0
        .set    reorder
        END(resume)

/*
 * Save a thread's fp context.
 */
LEAF(_save_fp)
        FPU_SAVE_SINGLE(a0, t1)                 # clobbers t1
        jr      ra
        END(_save_fp)

/*
 * Restore a thread's fp context.
 */
LEAF(_restore_fp)
        FPU_RESTORE_SINGLE(a0, t1)              # clobbers t1
        jr      ra
        END(_restore_fp)

/*
 * Load the FPU with signalling NANS.  This bit pattern we're using has
 * the property that no matter wether considered as single or as double
 * precision represents signaling NANS.
 *
 * We initialize fcr31 to rounding to nearest, no exceptions.
 */

#define FPU_DEFAULT  0x00000000

LEAF(_init_fpu)
        mfc0    t0, CP0_STATUS
        li      t1, ST0_CU1
        or      t0, t1
        mtc0    t0, CP0_STATUS

        li      t1, FPU_DEFAULT
        ctc1    t1, fcr31

        li      t0, -1

        mtc1    t0, $f0
        mtc1    t0, $f1
        mtc1    t0, $f2
        mtc1    t0, $f3
        mtc1    t0, $f4
        mtc1    t0, $f5
        mtc1    t0, $f6
        mtc1    t0, $f7
        mtc1    t0, $f8
        mtc1    t0, $f9
        mtc1    t0, $f10
        mtc1    t0, $f11
        mtc1    t0, $f12
        mtc1    t0, $f13
        mtc1    t0, $f14
        mtc1    t0, $f15
        mtc1    t0, $f16
        mtc1    t0, $f17
        mtc1    t0, $f18
        mtc1    t0, $f19
        mtc1    t0, $f20
        mtc1    t0, $f21
        mtc1    t0, $f22
        mtc1    t0, $f23
        mtc1    t0, $f24
        mtc1    t0, $f25
        mtc1    t0, $f26
        mtc1    t0, $f27
        mtc1    t0, $f28
        mtc1    t0, $f29
        mtc1    t0, $f30
        .set    noreorder
        jr      ra
         mtc1   t0, $f31
        .set    reorder
        END(_init_fpu)