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