1/* 2 * fpu.c - save/restore of Floating Point Unit Registers on task switch 3 * 4 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) 5 * 6 * This program is free software; you can redistribute it and/or modify 7 * it under the terms of the GNU General Public License version 2 as 8 * published by the Free Software Foundation. 9 */ 10 11#include <linux/sched.h> 12#include <asm/switch_to.h> 13 14/* 15 * To save/restore FPU regs, simplest scheme would use LR/SR insns. 16 * However since SR serializes the pipeline, an alternate "hack" can be used 17 * which uses the FPU Exchange insn (DEXCL) to r/w FPU regs. 18 * 19 * Store to 64bit dpfp1 reg from a pair of core regs: 20 * dexcl1 0, r1, r0 ; where r1:r0 is the 64 bit val 21 * 22 * Read from dpfp1 into pair of core regs (w/o clobbering dpfp1) 23 * mov_s r3, 0 24 * daddh11 r1, r3, r3 ; get "hi" into r1 (dpfp1 unchanged) 25 * dexcl1 r0, r1, r3 ; get "low" into r0 (dpfp1 low clobbered) 26 * dexcl1 0, r1, r0 ; restore dpfp1 to orig value 27 * 28 * However we can tweak the read, so that read-out of outgoing task's FPU regs 29 * and write of incoming task's regs happen in one shot. So all the work is 30 * done before context switch 31 */ 32 33void fpu_save_restore(struct task_struct *prev, struct task_struct *next) 34{ 35 unsigned int *saveto = &prev->thread.fpu.aux_dpfp[0].l; 36 unsigned int *readfrom = &next->thread.fpu.aux_dpfp[0].l; 37 38 const unsigned int zero = 0; 39 40 __asm__ __volatile__( 41 "daddh11 %0, %2, %2\n" 42 "dexcl1 %1, %3, %4\n" 43 : "=&r" (*(saveto + 1)), /* early clobber must here */ 44 "=&r" (*(saveto)) 45 : "r" (zero), "r" (*(readfrom + 1)), "r" (*(readfrom)) 46 ); 47 48 __asm__ __volatile__( 49 "daddh22 %0, %2, %2\n" 50 "dexcl2 %1, %3, %4\n" 51 : "=&r"(*(saveto + 3)), /* early clobber must here */ 52 "=&r"(*(saveto + 2)) 53 : "r" (zero), "r" (*(readfrom + 3)), "r" (*(readfrom + 2)) 54 ); 55} 56