xref: /openbmc/linux/arch/arc/kernel/fpu.c (revision 3a715e80)
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 
fpu_save_restore(struct task_struct * prev,struct task_struct * next)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 
fpu_init_task(struct pt_regs * regs)58 void 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 
fpu_save_restore(struct task_struct * prev,struct task_struct * next)69 void 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