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// SPDX-License-Identifier: GPL-2.0-only
/*
* fpu.c - save/restore of Floating Point Unit Registers on task switch
*
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
*/
#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))
);
}
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