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/fpu.h> 10 11 #ifdef CONFIG_ISA_ARCOMPACT 12 13 /* 14 * To save/restore FPU regs, simplest scheme would use LR/SR insns. 15 * However since SR serializes the pipeline, an alternate "hack" can be used 16 * which uses the FPU Exchange insn (DEXCL) to r/w FPU regs. 17 * 18 * Store to 64bit dpfp1 reg from a pair of core regs: 19 * dexcl1 0, r1, r0 ; where r1:r0 is the 64 bit val 20 * 21 * Read from dpfp1 into pair of core regs (w/o clobbering dpfp1) 22 * mov_s r3, 0 23 * daddh11 r1, r3, r3 ; get "hi" into r1 (dpfp1 unchanged) 24 * dexcl1 r0, r1, r3 ; get "low" into r0 (dpfp1 low clobbered) 25 * dexcl1 0, r1, r0 ; restore dpfp1 to orig value 26 * 27 * However we can tweak the read, so that read-out of outgoing task's FPU regs 28 * and write of incoming task's regs happen in one shot. So all the work is 29 * done before context switch 30 */ 31 32 void fpu_save_restore(struct task_struct *prev, struct task_struct *next) 33 { 34 unsigned int *saveto = &prev->thread.fpu.aux_dpfp[0].l; 35 unsigned int *readfrom = &next->thread.fpu.aux_dpfp[0].l; 36 37 const unsigned int zero = 0; 38 39 __asm__ __volatile__( 40 "daddh11 %0, %2, %2\n" 41 "dexcl1 %1, %3, %4\n" 42 : "=&r" (*(saveto + 1)), /* early clobber must here */ 43 "=&r" (*(saveto)) 44 : "r" (zero), "r" (*(readfrom + 1)), "r" (*(readfrom)) 45 ); 46 47 __asm__ __volatile__( 48 "daddh22 %0, %2, %2\n" 49 "dexcl2 %1, %3, %4\n" 50 : "=&r"(*(saveto + 3)), /* early clobber must here */ 51 "=&r"(*(saveto + 2)) 52 : "r" (zero), "r" (*(readfrom + 3)), "r" (*(readfrom + 2)) 53 ); 54 } 55 56 #else 57 58 void fpu_init_task(struct pt_regs *regs) 59 { 60 /* default rounding mode */ 61 write_aux_reg(ARC_REG_FPU_CTRL, 0x100); 62 63 /* set "Write enable" to allow explicit write to exception flags */ 64 write_aux_reg(ARC_REG_FPU_STATUS, 0x80000000); 65 } 66 67 void fpu_save_restore(struct task_struct *prev, struct task_struct *next) 68 { 69 struct arc_fpu *save = &prev->thread.fpu; 70 struct arc_fpu *restore = &next->thread.fpu; 71 72 save->ctrl = read_aux_reg(ARC_REG_FPU_CTRL); 73 save->status = read_aux_reg(ARC_REG_FPU_STATUS); 74 75 write_aux_reg(ARC_REG_FPU_CTRL, restore->ctrl); 76 write_aux_reg(ARC_REG_FPU_STATUS, restore->status); 77 } 78 79 #endif 80