1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * fpu.c - save/restore of Floating Point Unit Registers on task switch 4 * 5 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) 6 */ 7 8 #include <linux/sched.h> 9 #include <asm/switch_to.h> 10 11 /* 12 * To save/restore FPU regs, simplest scheme would use LR/SR insns. 13 * However since SR serializes the pipeline, an alternate "hack" can be used 14 * which uses the FPU Exchange insn (DEXCL) to r/w FPU regs. 15 * 16 * Store to 64bit dpfp1 reg from a pair of core regs: 17 * dexcl1 0, r1, r0 ; where r1:r0 is the 64 bit val 18 * 19 * Read from dpfp1 into pair of core regs (w/o clobbering dpfp1) 20 * mov_s r3, 0 21 * daddh11 r1, r3, r3 ; get "hi" into r1 (dpfp1 unchanged) 22 * dexcl1 r0, r1, r3 ; get "low" into r0 (dpfp1 low clobbered) 23 * dexcl1 0, r1, r0 ; restore dpfp1 to orig value 24 * 25 * However we can tweak the read, so that read-out of outgoing task's FPU regs 26 * and write of incoming task's regs happen in one shot. So all the work is 27 * done before context switch 28 */ 29 30 void fpu_save_restore(struct task_struct *prev, struct task_struct *next) 31 { 32 unsigned int *saveto = &prev->thread.fpu.aux_dpfp[0].l; 33 unsigned int *readfrom = &next->thread.fpu.aux_dpfp[0].l; 34 35 const unsigned int zero = 0; 36 37 __asm__ __volatile__( 38 "daddh11 %0, %2, %2\n" 39 "dexcl1 %1, %3, %4\n" 40 : "=&r" (*(saveto + 1)), /* early clobber must here */ 41 "=&r" (*(saveto)) 42 : "r" (zero), "r" (*(readfrom + 1)), "r" (*(readfrom)) 43 ); 44 45 __asm__ __volatile__( 46 "daddh22 %0, %2, %2\n" 47 "dexcl2 %1, %3, %4\n" 48 : "=&r"(*(saveto + 3)), /* early clobber must here */ 49 "=&r"(*(saveto + 2)) 50 : "r" (zero), "r" (*(readfrom + 3)), "r" (*(readfrom + 2)) 51 ); 52 } 53