linux/arch/mips/kernel/r2300_switch.S
Atsushi Nemoto 5323180db7 [MIPS] Disallow CpU exception in kernel again.
The commit 4d40bff7110e9e1a97ff8c01bdd6350e9867cc10 ("Allow CpU
exception in kernel partially") was broken.  The commit was to fix
theoretical problem but broke usual case.  Revert it for now.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2007-04-20 14:58:37 +01:00

174 lines
3.4 KiB
ArmAsm

/*
* 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 <asm/asm.h>
#include <asm/cachectl.h>
#include <asm/fpregdef.h>
#include <asm/mipsregs.h>
#include <asm/asm-offsets.h>
#include <asm/page.h>
#include <asm/regdef.h>
#include <asm/stackframe.h>
#include <asm/thread_info.h>
#include <asm/asmmacro.h>
.set mips1
.align 5
/*
* Offset to the current process status flags, the first 32 bytes of the
* stack are not used.
*/
#define ST_OFF (_THREAD_SIZE - 32 - PT_SIZE + PT_STATUS)
/*
* FPU context is saved iff the process has used it's FPU in the current
* time slice as indicated by TIF_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,
* struct thread_info *next_ti) )
*/
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 t3, TASK_THREAD_INFO(a0)
lw t0, TI_FLAGS(t3)
li t1, _TIF_USEDFPU
and t2, t0, t1
beqz t2, 1f
nor t1, zero, t1
and t0, t0, t1
sw t0, TI_FLAGS(t3)
/*
* clear saved user stack CU1 bit
*/
lw t0, ST_OFF(t3)
li t1, ~ST0_CU1
and t0, t0, t1
sw t0, ST_OFF(t3)
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, a2
cpu_restore_nonscratch a1
addiu t1, $28, _THREAD_SIZE - 32
sw t1, kernelsp
mfc0 t1, CP0_STATUS /* Do we really need this? */
li a3, 0xff01
and t1, a3
lw a2, THREAD_STATUS(a1)
nor a3, $0, a3
and a2, a3
or a2, t1
mtc0 a2, CP0_STATUS
move v0, a0
jr ra
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 whether 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
mtc1 t0, $f31
jr ra
END(_init_fpu)