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
32void 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
58void fpu_init_task(struct pt_regs *regs)
59{
60 const unsigned int fwe = 0x80000000;
61
62 /* default rounding mode */
63 write_aux_reg(ARC_REG_FPU_CTRL, 0x100);
64
65 /* Initialize to zero: setting requires FWE be set */
66 write_aux_reg(ARC_REG_FPU_STATUS, fwe);
67}
68
69void fpu_save_restore(struct task_struct *prev, struct task_struct *next)
70{
71 struct arc_fpu *save = &prev->thread.fpu;
72 struct arc_fpu *restore = &next->thread.fpu;
73 const unsigned int fwe = 0x80000000;
74
75 save->ctrl = read_aux_reg(ARC_REG_FPU_CTRL);
76 save->status = read_aux_reg(ARC_REG_FPU_STATUS);
77
78 write_aux_reg(ARC_REG_FPU_CTRL, restore->ctrl);
79 write_aux_reg(ARC_REG_FPU_STATUS, (fwe | restore->status));
80}
81
82#endif
83

source code of linux/arch/arc/kernel/fpu.c