linux/arch/mips/include/asm/fpu.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Copyright (C) 2002 MontaVista Software Inc.
 * Author: Jun Sun, jsun@mvista.com or jsun@junsun.net
 */
#ifndef _ASM_FPU_H
#define _ASM_FPU_H

#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/ptrace.h>
#include <linux/thread_info.h>
#include <linux/bitops.h>

#include <asm/mipsregs.h>
#include <asm/cpu.h>
#include <asm/cpu-features.h>
#include <asm/fpu_emulator.h>
#include <asm/hazards.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
#include <asm/current.h>
#include <asm/msa.h>

#ifdef CONFIG_MIPS_MT_FPAFF
#include <asm/mips_mt.h>
#endif

/*
 * This enum specifies a mode in which we want the FPU to operate, for cores
 * which implement the Status.FR bit. Note that the bottom bit of the value
 * purposefully matches the desired value of the Status.FR bit.
 */
enum fpu_mode {
	FPU_32BIT = 0,		/* FR = 0 */
	FPU_64BIT,		/* FR = 1, FRE = 0 */
	FPU_AS_IS,
	FPU_HYBRID,		/* FR = 1, FRE = 1 */

#define FPU_FR_MASK		0x1
};

#ifdef CONFIG_MIPS_FP_SUPPORT

extern void _save_fp(struct task_struct *);
extern void _restore_fp(struct task_struct *);

#define __disable_fpu()							\
do {									\
	clear_c0_status(ST0_CU1);					\
	disable_fpu_hazard();						\
} while (0)

static inline int __enable_fpu(enum fpu_mode mode)
{
	int fr;

	switch (mode) {
	case FPU_AS_IS:
		/* just enable the FPU in its current mode */
		set_c0_status(ST0_CU1);
		enable_fpu_hazard();
		return 0;

	case FPU_HYBRID:
		if (!cpu_has_fre)
			return SIGFPE;

		/* set FRE */
		set_c0_config5(MIPS_CONF5_FRE);
		goto fr_common;

	case FPU_64BIT:
#if !(defined(CONFIG_CPU_MIPSR2) || defined(CONFIG_CPU_MIPSR5) || \
      defined(CONFIG_CPU_MIPSR6) || defined(CONFIG_64BIT))
		/* we only have a 32-bit FPU */
		return SIGFPE;
#endif
		/* fallthrough */
	case FPU_32BIT:
		if (cpu_has_fre) {
			/* clear FRE */
			clear_c0_config5(MIPS_CONF5_FRE);
		}
fr_common:
		/* set CU1 & change FR appropriately */
		fr = (int)mode & FPU_FR_MASK;
		change_c0_status(ST0_CU1 | ST0_FR, ST0_CU1 | (fr ? ST0_FR : 0));
		enable_fpu_hazard();

		/* check FR has the desired value */
		if (!!(read_c0_status() & ST0_FR) == !!fr)
			return 0;

		/* unsupported FR value */
		__disable_fpu();
		return SIGFPE;

	default:
		BUG();
	}

	return SIGFPE;
}

#define clear_fpu_owner()	clear_thread_flag(TIF_USEDFPU)

static inline int __is_fpu_owner(void)
{
	return test_thread_flag(TIF_USEDFPU);
}

static inline int is_fpu_owner(void)
{
	return cpu_has_fpu && __is_fpu_owner();
}

static inline int __own_fpu(void)
{
	enum fpu_mode mode;
	int ret;

	if (test_thread_flag(TIF_HYBRID_FPREGS))
		mode = FPU_HYBRID;
	else
		mode = !test_thread_flag(TIF_32BIT_FPREGS);

	ret = __enable_fpu(mode);
	if (ret)
		return ret;

	if (current->thread.fpu.fcr31 & FPU_CSR_NAN2008) {
		if (!cpu_has_nan_2008) {
			ret = SIGFPE;
			goto failed;
		}
	} else {
		if (!cpu_has_nan_legacy) {
			ret = SIGFPE;
			goto failed;
		}
	}

	KSTK_STATUS(current) |= ST0_CU1;
	if (mode == FPU_64BIT || mode == FPU_HYBRID)
		KSTK_STATUS(current) |= ST0_FR;
	else /* mode == FPU_32BIT */
		KSTK_STATUS(current) &= ~ST0_FR;

	set_thread_flag(TIF_USEDFPU);
	return 0;
failed:
	__disable_fpu();
	return ret;
}

static inline int own_fpu_inatomic(int restore)
{
	int ret = 0;

	if (cpu_has_fpu && !__is_fpu_owner()) {
		ret = __own_fpu();
		if (restore && !ret)
			_restore_fp(current);
	}
	return ret;
}

static inline int own_fpu(int restore)
{
	int ret;

	preempt_disable();
	ret = own_fpu_inatomic(restore);
	preempt_enable();
	return ret;
}

static inline void lose_fpu_inatomic(int save, struct task_struct *tsk)
{
	if (is_msa_enabled()) {
		if (save) {
			save_msa(tsk);
			tsk->thread.fpu.fcr31 =
					read_32bit_cp1_register(CP1_STATUS);
		}
		disable_msa();
		clear_tsk_thread_flag(tsk, TIF_USEDMSA);
		__disable_fpu();
	} else if (is_fpu_owner()) {
		if (save)
			_save_fp(tsk);
		__disable_fpu();
	} else {
		/* FPU should not have been left enabled with no owner */
		WARN(read_c0_status() & ST0_CU1,
		     "Orphaned FPU left enabled");
	}
	KSTK_STATUS(tsk) &= ~ST0_CU1;
	clear_tsk_thread_flag(tsk, TIF_USEDFPU);
}

static inline void lose_fpu(int save)
{
	preempt_disable();
	lose_fpu_inatomic(save, current);
	preempt_enable();
}

/**
 * init_fp_ctx() - Initialize task FP context
 * @target: The task whose FP context should be initialized.
 *
 * Initializes the FP context of the target task to sane default values if that
 * target task does not already have valid FP context. Once the context has
 * been initialized, the task will be marked as having used FP & thus having
 * valid FP context.
 *
 * Returns: true if context is initialized, else false.
 */
static inline bool init_fp_ctx(struct task_struct *target)
{
	/* If FP has been used then the target already has context */
	if (tsk_used_math(target))
		return false;

	/* Begin with data registers set to all 1s... */
	memset(&target->thread.fpu.fpr, ~0, sizeof(target->thread.fpu.fpr));

	/* FCSR has been preset by `mips_set_personality_nan'.  */

	/*
	 * Record that the target has "used" math, such that the context
	 * just initialised, and any modifications made by the caller,
	 * aren't discarded.
	 */
	set_stopped_child_used_math(target);

	return true;
}

static inline void save_fp(struct task_struct *tsk)
{
	if (cpu_has_fpu)
		_save_fp(tsk);
}

static inline void restore_fp(struct task_struct *tsk)
{
	if (cpu_has_fpu)
		_restore_fp(tsk);
}

static inline union fpureg *get_fpu_regs(struct task_struct *tsk)
{
	if (tsk == current) {
		preempt_disable();
		if (is_fpu_owner())
			_save_fp(current);
		preempt_enable();
	}

	return tsk->thread.fpu.fpr;
}

#else /* !CONFIG_MIPS_FP_SUPPORT */

/*
 * When FP support is disabled we provide only a minimal set of stub functions
 * to avoid callers needing to care too much about CONFIG_MIPS_FP_SUPPORT.
 */

static inline int __enable_fpu(enum fpu_mode mode)
{
	return SIGILL;
}

static inline void __disable_fpu(void)
{
	/* no-op */
}


static inline int is_fpu_owner(void)
{
	return 0;
}

static inline void clear_fpu_owner(void)
{
	/* no-op */
}

static inline int own_fpu_inatomic(int restore)
{
	return SIGILL;
}

static inline int own_fpu(int restore)
{
	return SIGILL;
}

static inline void lose_fpu_inatomic(int save, struct task_struct *tsk)
{
	/* no-op */
}

static inline void lose_fpu(int save)
{
	/* no-op */
}

static inline bool init_fp_ctx(struct task_struct *target)
{
	return false;
}

/*
 * The following functions should only be called in paths where we know that FP
 * support is enabled, typically a path where own_fpu() or __enable_fpu() have
 * returned successfully. When CONFIG_MIPS_FP_SUPPORT=n it is known at compile
 * time that this should never happen, so calls to these functions should be
 * optimized away & never actually be emitted.
 */

extern void save_fp(struct task_struct *tsk)
	__compiletime_error("save_fp() should not be called when CONFIG_MIPS_FP_SUPPORT=n");

extern void _save_fp(struct task_struct *)
	__compiletime_error("_save_fp() should not be called when CONFIG_MIPS_FP_SUPPORT=n");

extern void restore_fp(struct task_struct *tsk)
	__compiletime_error("restore_fp() should not be called when CONFIG_MIPS_FP_SUPPORT=n");

extern void _restore_fp(struct task_struct *)
	__compiletime_error("_restore_fp() should not be called when CONFIG_MIPS_FP_SUPPORT=n");

extern union fpureg *get_fpu_regs(struct task_struct *tsk)
	__compiletime_error("get_fpu_regs() should not be called when CONFIG_MIPS_FP_SUPPORT=n");

#endif /* !CONFIG_MIPS_FP_SUPPORT */
#endif /* _ASM_FPU_H */