56 lines
1.8 KiB
C
56 lines
1.8 KiB
C
|
/*
|
||
|
|
* fpu.c - save/restore of Floating Point Unit Registers on task switch
|
||
|
|
*
|
||
|
|
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
|
||
|
|
*
|
||
|
|
* This program is free software; you can redistribute it and/or modify
|
||
|
|
* it under the terms of the GNU General Public License version 2 as
|
||
|
|
* published by the Free Software Foundation.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include <linux/sched.h>
|
||
|
|
#include <asm/switch_to.h>
|
||
|
|
|
||
|
|
/*
|
||
|
|
* To save/restore FPU regs, simplest scheme would use LR/SR insns.
|
||
|
|
* However since SR serializes the pipeline, an alternate "hack" can be used
|
||
|
|
* which uses the FPU Exchange insn (DEXCL) to r/w FPU regs.
|
||
|
|
*
|
||
|
|
* Store to 64bit dpfp1 reg from a pair of core regs:
|
||
|
|
* dexcl1 0, r1, r0 ; where r1:r0 is the 64 bit val
|
||
|
|
*
|
||
|
|
* Read from dpfp1 into pair of core regs (w/o clobbering dpfp1)
|
||
|
|
* mov_s r3, 0
|
||
|
|
* daddh11 r1, r3, r3 ; get "hi" into r1 (dpfp1 unchanged)
|
||
|
|
* dexcl1 r0, r1, r3 ; get "low" into r0 (dpfp1 low clobbered)
|
||
|
|
* dexcl1 0, r1, r0 ; restore dpfp1 to orig value
|
||
|
|
*
|
||
|
|
* However we can tweak the read, so that read-out of outgoing task's FPU regs
|
||
|
|
* and write of incoming task's regs happen in one shot. So all the work is
|
||
|
|
* done before context switch
|
||
|
|
*/
|
||
|
|
|
||
|
|
void fpu_save_restore(struct task_struct *prev, struct task_struct *next)
|
||
|
|
{
|
||
|
|
unsigned int *saveto = &prev->thread.fpu.aux_dpfp[0].l;
|
||
|
|
unsigned int *readfrom = &next->thread.fpu.aux_dpfp[0].l;
|
||
|
|
|
||
|
|
const unsigned int zero = 0;
|
||
|
|
|
||
|
|
__asm__ __volatile__(
|
||
|
|
"daddh11 %0, %2, %2\n"
|
||
|
|
"dexcl1 %1, %3, %4\n"
|
||
|
|
: "=&r" (*(saveto + 1)), /* early clobber must here */
|
||
|
|
"=&r" (*(saveto))
|
||
|
|
: "r" (zero), "r" (*(readfrom + 1)), "r" (*(readfrom))
|
||
|
|
);
|
||
|
|
|
||
|
|
__asm__ __volatile__(
|
||
|
|
"daddh22 %0, %2, %2\n"
|
||
|
|
"dexcl2 %1, %3, %4\n"
|
||
|
|
: "=&r"(*(saveto + 3)), /* early clobber must here */
|
||
|
|
"=&r"(*(saveto + 2))
|
||
|
|
: "r" (zero), "r" (*(readfrom + 3)), "r" (*(readfrom + 2))
|
||
|
|
);
|
||
|
|
}
|