xref: /openbmc/linux/arch/s390/include/asm/fpu/api.h (revision 0ef9d78b)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * In-kernel FPU support functions
4  *
5  *
6  * Consider these guidelines before using in-kernel FPU functions:
7  *
8  *  1. Use kernel_fpu_begin() and kernel_fpu_end() to enclose all in-kernel
9  *     use of floating-point or vector registers and instructions.
10  *
11  *  2. For kernel_fpu_begin(), specify the vector register range you want to
12  *     use with the KERNEL_VXR_* constants. Consider these usage guidelines:
13  *
14  *     a) If your function typically runs in process-context, use the lower
15  *	  half of the vector registers, for example, specify KERNEL_VXR_LOW.
16  *     b) If your function typically runs in soft-irq or hard-irq context,
17  *	  prefer using the upper half of the vector registers, for example,
18  *	  specify KERNEL_VXR_HIGH.
19  *
20  *     If you adhere to these guidelines, an interrupted process context
21  *     does not require to save and restore vector registers because of
22  *     disjoint register ranges.
23  *
24  *     Also note that the __kernel_fpu_begin()/__kernel_fpu_end() functions
25  *     includes logic to save and restore up to 16 vector registers at once.
26  *
27  *  3. You can nest kernel_fpu_begin()/kernel_fpu_end() by using different
28  *     struct kernel_fpu states.  Vector registers that are in use by outer
29  *     levels are saved and restored.  You can minimize the save and restore
30  *     effort by choosing disjoint vector register ranges.
31  *
32  *  5. To use vector floating-point instructions, specify the KERNEL_FPC
33  *     flag to save and restore floating-point controls in addition to any
34  *     vector register range.
35  *
36  *  6. To use floating-point registers and instructions only, specify the
37  *     KERNEL_FPR flag.  This flag triggers a save and restore of vector
38  *     registers V0 to V15 and floating-point controls.
39  *
40  * Copyright IBM Corp. 2015
41  * Author(s): Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
42  */
43 
44 #ifndef _ASM_S390_FPU_API_H
45 #define _ASM_S390_FPU_API_H
46 
47 #include <linux/preempt.h>
48 #include <asm/asm-extable.h>
49 
50 void save_fpu_regs(void);
51 void load_fpu_regs(void);
52 void __load_fpu_regs(void);
53 
54 static inline int test_fp_ctl(u32 fpc)
55 {
56 	u32 orig_fpc;
57 	int rc;
58 
59 	asm volatile(
60 		"	efpc    %1\n"
61 		"	sfpc	%2\n"
62 		"0:	sfpc	%1\n"
63 		"	la	%0,0\n"
64 		"1:\n"
65 		EX_TABLE(0b,1b)
66 		: "=d" (rc), "=&d" (orig_fpc)
67 		: "d" (fpc), "0" (-EINVAL));
68 	return rc;
69 }
70 
71 #define KERNEL_FPC		1
72 #define KERNEL_VXR_V0V7		2
73 #define KERNEL_VXR_V8V15	4
74 #define KERNEL_VXR_V16V23	8
75 #define KERNEL_VXR_V24V31	16
76 
77 #define KERNEL_VXR_LOW		(KERNEL_VXR_V0V7|KERNEL_VXR_V8V15)
78 #define KERNEL_VXR_MID		(KERNEL_VXR_V8V15|KERNEL_VXR_V16V23)
79 #define KERNEL_VXR_HIGH		(KERNEL_VXR_V16V23|KERNEL_VXR_V24V31)
80 
81 #define KERNEL_VXR		(KERNEL_VXR_LOW|KERNEL_VXR_HIGH)
82 #define KERNEL_FPR		(KERNEL_FPC|KERNEL_VXR_LOW)
83 
84 struct kernel_fpu;
85 
86 /*
87  * Note the functions below must be called with preemption disabled.
88  * Do not enable preemption before calling __kernel_fpu_end() to prevent
89  * an corruption of an existing kernel FPU state.
90  *
91  * Prefer using the kernel_fpu_begin()/kernel_fpu_end() pair of functions.
92  */
93 void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
94 void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
95 
96 
97 static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags)
98 {
99 	preempt_disable();
100 	state->mask = S390_lowcore.fpu_flags;
101 	if (!test_cpu_flag(CIF_FPU))
102 		/* Save user space FPU state and register contents */
103 		save_fpu_regs();
104 	else if (state->mask & flags)
105 		/* Save FPU/vector register in-use by the kernel */
106 		__kernel_fpu_begin(state, flags);
107 	S390_lowcore.fpu_flags |= flags;
108 }
109 
110 static inline void kernel_fpu_end(struct kernel_fpu *state, u32 flags)
111 {
112 	S390_lowcore.fpu_flags = state->mask;
113 	if (state->mask & flags)
114 		/* Restore FPU/vector register in-use by the kernel */
115 		__kernel_fpu_end(state, flags);
116 	preempt_enable();
117 }
118 
119 #endif /* _ASM_S390_FPU_API_H */
120