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