Linux 5.7.7

[linux/fpc-iii.git] / arch / arm / vfp / vfpmodule.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/arch/arm/vfp/vfpmodule.c
 *
 *  Copyright (C) 2004 ARM Limited.
 *  Written by Deep Blue Solutions Limited.
 */
#include <linux/types.h>
#include <linux/cpu.h>
#include <linux/cpu_pm.h>
#include <linux/hardirq.h>
#include <linux/kernel.h>
#include <linux/notifier.h>
#include <linux/signal.h>
#include <linux/sched/signal.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/uaccess.h>
#include <linux/user.h>
#include <linux/export.h>

#include <asm/cp15.h>
#include <asm/cputype.h>
#include <asm/system_info.h>
#include <asm/thread_notify.h>
#include <asm/vfp.h>

#include "vfpinstr.h"
#include "vfp.h"

/*
 * Our undef handlers (in entry.S)
 */
asmlinkage void vfp_testing_entry(void);
asmlinkage void vfp_support_entry(void);
asmlinkage void vfp_null_entry(void);

asmlinkage void (*vfp_vector)(void) = vfp_null_entry;

/*
 * Dual-use variable.
 * Used in startup: set to non-zero if VFP checks fail
 * After startup, holds VFP architecture
 */
unsigned int VFP_arch;

/*
 * The pointer to the vfpstate structure of the thread which currently
 * owns the context held in the VFP hardware, or NULL if the hardware
 * context is invalid.
 *
 * For UP, this is sufficient to tell which thread owns the VFP context.
 * However, for SMP, we also need to check the CPU number stored in the
 * saved state too to catch migrations.
 */
union vfp_state *vfp_current_hw_state[NR_CPUS];

/*
 * Is 'thread's most up to date state stored in this CPUs hardware?
 * Must be called from non-preemptible context.
 */
static bool vfp_state_in_hw(unsigned int cpu, struct thread_info *thread)
{
#ifdef CONFIG_SMP
        if (thread->vfpstate.hard.cpu != cpu)
                return false;
#endif
        return vfp_current_hw_state[cpu] == &thread->vfpstate;
}

/*
 * Force a reload of the VFP context from the thread structure.  We do
 * this by ensuring that access to the VFP hardware is disabled, and
 * clear vfp_current_hw_state.  Must be called from non-preemptible context.
 */
static void vfp_force_reload(unsigned int cpu, struct thread_info *thread)
{
        if (vfp_state_in_hw(cpu, thread)) {
                fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
                vfp_current_hw_state[cpu] = NULL;
        }
#ifdef CONFIG_SMP
        thread->vfpstate.hard.cpu = NR_CPUS;
#endif
}

/*
 * Per-thread VFP initialization.
 */
static void vfp_thread_flush(struct thread_info *thread)
{
        union vfp_state *vfp = &thread->vfpstate;
        unsigned int cpu;

        /*
         * Disable VFP to ensure we initialize it first.  We must ensure
         * that the modification of vfp_current_hw_state[] and hardware
         * disable are done for the same CPU and without preemption.
         *
         * Do this first to ensure that preemption won't overwrite our
         * state saving should access to the VFP be enabled at this point.
         */
        cpu = get_cpu();
        if (vfp_current_hw_state[cpu] == vfp)
                vfp_current_hw_state[cpu] = NULL;
        fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
        put_cpu();

        memset(vfp, 0, sizeof(union vfp_state));

        vfp->hard.fpexc = FPEXC_EN;
        vfp->hard.fpscr = FPSCR_ROUND_NEAREST;
#ifdef CONFIG_SMP
        vfp->hard.cpu = NR_CPUS;
#endif
}

static void vfp_thread_exit(struct thread_info *thread)
{
        /* release case: Per-thread VFP cleanup. */
        union vfp_state *vfp = &thread->vfpstate;
        unsigned int cpu = get_cpu();

        if (vfp_current_hw_state[cpu] == vfp)
                vfp_current_hw_state[cpu] = NULL;
        put_cpu();
}

static void vfp_thread_copy(struct thread_info *thread)
{
        struct thread_info *parent = current_thread_info();

        vfp_sync_hwstate(parent);
        thread->vfpstate = parent->vfpstate;
#ifdef CONFIG_SMP
        thread->vfpstate.hard.cpu = NR_CPUS;
#endif
}

/*
 * When this function is called with the following 'cmd's, the following
 * is true while this function is being run:
 *  THREAD_NOFTIFY_SWTICH:
 *   - the previously running thread will not be scheduled onto another CPU.
 *   - the next thread to be run (v) will not be running on another CPU.
 *   - thread->cpu is the local CPU number
 *   - not preemptible as we're called in the middle of a thread switch
 *  THREAD_NOTIFY_FLUSH:
 *   - the thread (v) will be running on the local CPU, so
 *      v === current_thread_info()
 *   - thread->cpu is the local CPU number at the time it is accessed,
 *      but may change at any time.
 *   - we could be preempted if tree preempt rcu is enabled, so
 *      it is unsafe to use thread->cpu.
 *  THREAD_NOTIFY_EXIT
 *   - we could be preempted if tree preempt rcu is enabled, so
 *      it is unsafe to use thread->cpu.
 */
static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
{
        struct thread_info *thread = v;
        u32 fpexc;
#ifdef CONFIG_SMP
        unsigned int cpu;
#endif

        switch (cmd) {
        case THREAD_NOTIFY_SWITCH:
                fpexc = fmrx(FPEXC);

#ifdef CONFIG_SMP
                cpu = thread->cpu;

                /*
                 * On SMP, if VFP is enabled, save the old state in
                 * case the thread migrates to a different CPU. The
                 * restoring is done lazily.
                 */
                if ((fpexc & FPEXC_EN) && vfp_current_hw_state[cpu])
                        vfp_save_state(vfp_current_hw_state[cpu], fpexc);
#endif

                /*
                 * Always disable VFP so we can lazily save/restore the
                 * old state.
                 */
                fmxr(FPEXC, fpexc & ~FPEXC_EN);
                break;

        case THREAD_NOTIFY_FLUSH:
                vfp_thread_flush(thread);
                break;

        case THREAD_NOTIFY_EXIT:
                vfp_thread_exit(thread);
                break;

        case THREAD_NOTIFY_COPY:
                vfp_thread_copy(thread);
                break;
        }

        return NOTIFY_DONE;
}

static struct notifier_block vfp_notifier_block = {
        .notifier_call  = vfp_notifier,
};

/*
 * Raise a SIGFPE for the current process.
 * sicode describes the signal being raised.
 */
static void vfp_raise_sigfpe(unsigned int sicode, struct pt_regs *regs)
{
        /*
         * This is the same as NWFPE, because it's not clear what
         * this is used for
         */
        current->thread.error_code = 0;
        current->thread.trap_no = 6;

        send_sig_fault(SIGFPE, sicode,
                       (void __user *)(instruction_pointer(regs) - 4),
                       current);
}

static void vfp_panic(char *reason, u32 inst)
{
        int i;

        pr_err("VFP: Error: %s\n", reason);
        pr_err("VFP: EXC 0x%08x SCR 0x%08x INST 0x%08x\n",
                fmrx(FPEXC), fmrx(FPSCR), inst);
        for (i = 0; i < 32; i += 2)
                pr_err("VFP: s%2u: 0x%08x s%2u: 0x%08x\n",
                       i, vfp_get_float(i), i+1, vfp_get_float(i+1));
}

/*
 * Process bitmask of exception conditions.
 */
static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_regs *regs)
{
        int si_code = 0;

        pr_debug("VFP: raising exceptions %08x\n", exceptions);

        if (exceptions == VFP_EXCEPTION_ERROR) {
                vfp_panic("unhandled bounce", inst);
                vfp_raise_sigfpe(FPE_FLTINV, regs);
                return;
        }

        /*
         * If any of the status flags are set, update the FPSCR.
         * Comparison instructions always return at least one of
         * these flags set.
         */
        if (exceptions & (FPSCR_N|FPSCR_Z|FPSCR_C|FPSCR_V))
                fpscr &= ~(FPSCR_N|FPSCR_Z|FPSCR_C|FPSCR_V);

        fpscr |= exceptions;

        fmxr(FPSCR, fpscr);

#define RAISE(stat,en,sig)                              \
        if (exceptions & stat && fpscr & en)            \
                si_code = sig;

        /*
         * These are arranged in priority order, least to highest.
         */
        RAISE(FPSCR_DZC, FPSCR_DZE, FPE_FLTDIV);
        RAISE(FPSCR_IXC, FPSCR_IXE, FPE_FLTRES);
        RAISE(FPSCR_UFC, FPSCR_UFE, FPE_FLTUND);
        RAISE(FPSCR_OFC, FPSCR_OFE, FPE_FLTOVF);
        RAISE(FPSCR_IOC, FPSCR_IOE, FPE_FLTINV);

        if (si_code)
                vfp_raise_sigfpe(si_code, regs);
}

/*
 * Emulate a VFP instruction.
 */
static u32 vfp_emulate_instruction(u32 inst, u32 fpscr, struct pt_regs *regs)
{
        u32 exceptions = VFP_EXCEPTION_ERROR;

        pr_debug("VFP: emulate: INST=0x%08x SCR=0x%08x\n", inst, fpscr);

        if (INST_CPRTDO(inst)) {
                if (!INST_CPRT(inst)) {
                        /*
                         * CPDO
                         */
                        if (vfp_single(inst)) {
                                exceptions = vfp_single_cpdo(inst, fpscr);
                        } else {
                                exceptions = vfp_double_cpdo(inst, fpscr);
                        }
                } else {
                        /*
                         * A CPRT instruction can not appear in FPINST2, nor
                         * can it cause an exception.  Therefore, we do not
                         * have to emulate it.
                         */
                }
        } else {
                /*
                 * A CPDT instruction can not appear in FPINST2, nor can
                 * it cause an exception.  Therefore, we do not have to
                 * emulate it.
                 */
        }
        return exceptions & ~VFP_NAN_FLAG;
}

/*
 * Package up a bounce condition.
 */
void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
{
        u32 fpscr, orig_fpscr, fpsid, exceptions;

        pr_debug("VFP: bounce: trigger %08x fpexc %08x\n", trigger, fpexc);

        /*
         * At this point, FPEXC can have the following configuration:
         *
         *  EX DEX IXE
         *  0   1   x   - synchronous exception
         *  1   x   0   - asynchronous exception
         *  1   x   1   - sychronous on VFP subarch 1 and asynchronous on later
         *  0   0   1   - synchronous on VFP9 (non-standard subarch 1
         *                implementation), undefined otherwise
         *
         * Clear various bits and enable access to the VFP so we can
         * handle the bounce.
         */
        fmxr(FPEXC, fpexc & ~(FPEXC_EX|FPEXC_DEX|FPEXC_FP2V|FPEXC_VV|FPEXC_TRAP_MASK));

        fpsid = fmrx(FPSID);
        orig_fpscr = fpscr = fmrx(FPSCR);

        /*
         * Check for the special VFP subarch 1 and FPSCR.IXE bit case
         */
        if ((fpsid & FPSID_ARCH_MASK) == (1 << FPSID_ARCH_BIT)
            && (fpscr & FPSCR_IXE)) {
                /*
                 * Synchronous exception, emulate the trigger instruction
                 */
                goto emulate;
        }

        if (fpexc & FPEXC_EX) {
#ifndef CONFIG_CPU_FEROCEON
                /*
                 * Asynchronous exception. The instruction is read from FPINST
                 * and the interrupted instruction has to be restarted.
                 */
                trigger = fmrx(FPINST);
                regs->ARM_pc -= 4;
#endif
        } else if (!(fpexc & FPEXC_DEX)) {
                /*
                 * Illegal combination of bits. It can be caused by an
                 * unallocated VFP instruction but with FPSCR.IXE set and not
                 * on VFP subarch 1.
                 */
                 vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr, regs);
                goto exit;
        }

        /*
         * Modify fpscr to indicate the number of iterations remaining.
         * If FPEXC.EX is 0, FPEXC.DEX is 1 and the FPEXC.VV bit indicates
         * whether FPEXC.VECITR or FPSCR.LEN is used.
         */
        if (fpexc & (FPEXC_EX | FPEXC_VV)) {
                u32 len;

                len = fpexc + (1 << FPEXC_LENGTH_BIT);

                fpscr &= ~FPSCR_LENGTH_MASK;
                fpscr |= (len & FPEXC_LENGTH_MASK) << (FPSCR_LENGTH_BIT - FPEXC_LENGTH_BIT);
        }

        /*
         * Handle the first FP instruction.  We used to take note of the
         * FPEXC bounce reason, but this appears to be unreliable.
         * Emulate the bounced instruction instead.
         */
        exceptions = vfp_emulate_instruction(trigger, fpscr, regs);
        if (exceptions)
                vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);

        /*
         * If there isn't a second FP instruction, exit now. Note that
         * the FPEXC.FP2V bit is valid only if FPEXC.EX is 1.
         */
        if ((fpexc & (FPEXC_EX | FPEXC_FP2V)) != (FPEXC_EX | FPEXC_FP2V))
                goto exit;

        /*
         * The barrier() here prevents fpinst2 being read
         * before the condition above.
         */
        barrier();
        trigger = fmrx(FPINST2);

 emulate:
        exceptions = vfp_emulate_instruction(trigger, orig_fpscr, regs);
        if (exceptions)
                vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
 exit:
        preempt_enable();
}

static void vfp_enable(void *unused)
{
        u32 access;

        BUG_ON(preemptible());
        access = get_copro_access();

        /*
         * Enable full access to VFP (cp10 and cp11)
         */
        set_copro_access(access | CPACC_FULL(10) | CPACC_FULL(11));
}

/* Called by platforms on which we want to disable VFP because it may not be
 * present on all CPUs within a SMP complex. Needs to be called prior to
 * vfp_init().
 */
void vfp_disable(void)
{
        if (VFP_arch) {
                pr_debug("%s: should be called prior to vfp_init\n", __func__);
                return;
        }
        VFP_arch = 1;
}

#ifdef CONFIG_CPU_PM
static int vfp_pm_suspend(void)
{
        struct thread_info *ti = current_thread_info();
        u32 fpexc = fmrx(FPEXC);

        /* if vfp is on, then save state for resumption */
        if (fpexc & FPEXC_EN) {
                pr_debug("%s: saving vfp state\n", __func__);
                vfp_save_state(&ti->vfpstate, fpexc);

                /* disable, just in case */
                fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
        } else if (vfp_current_hw_state[ti->cpu]) {
#ifndef CONFIG_SMP
                fmxr(FPEXC, fpexc | FPEXC_EN);
                vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
                fmxr(FPEXC, fpexc);
#endif
        }

        /* clear any information we had about last context state */
        vfp_current_hw_state[ti->cpu] = NULL;

        return 0;
}

static void vfp_pm_resume(void)
{
        /* ensure we have access to the vfp */
        vfp_enable(NULL);

        /* and disable it to ensure the next usage restores the state */
        fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
}

static int vfp_cpu_pm_notifier(struct notifier_block *self, unsigned long cmd,
        void *v)
{
        switch (cmd) {
        case CPU_PM_ENTER:
                vfp_pm_suspend();
                break;
        case CPU_PM_ENTER_FAILED:
        case CPU_PM_EXIT:
                vfp_pm_resume();
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block vfp_cpu_pm_notifier_block = {
        .notifier_call = vfp_cpu_pm_notifier,
};

static void vfp_pm_init(void)
{
        cpu_pm_register_notifier(&vfp_cpu_pm_notifier_block);
}

#else
static inline void vfp_pm_init(void) { }
#endif /* CONFIG_CPU_PM */

/*
 * Ensure that the VFP state stored in 'thread->vfpstate' is up to date
 * with the hardware state.
 */
void vfp_sync_hwstate(struct thread_info *thread)
{
        unsigned int cpu = get_cpu();

        if (vfp_state_in_hw(cpu, thread)) {
                u32 fpexc = fmrx(FPEXC);

                /*
                 * Save the last VFP state on this CPU.
                 */
                fmxr(FPEXC, fpexc | FPEXC_EN);
                vfp_save_state(&thread->vfpstate, fpexc | FPEXC_EN);
                fmxr(FPEXC, fpexc);
        }

        put_cpu();
}

/* Ensure that the thread reloads the hardware VFP state on the next use. */
void vfp_flush_hwstate(struct thread_info *thread)
{
        unsigned int cpu = get_cpu();

        vfp_force_reload(cpu, thread);

        put_cpu();
}

/*
 * Save the current VFP state into the provided structures and prepare
 * for entry into a new function (signal handler).
 */
int vfp_preserve_user_clear_hwstate(struct user_vfp *ufp,
                                    struct user_vfp_exc *ufp_exc)
{
        struct thread_info *thread = current_thread_info();
        struct vfp_hard_struct *hwstate = &thread->vfpstate.hard;

        /* Ensure that the saved hwstate is up-to-date. */
        vfp_sync_hwstate(thread);

        /*
         * Copy the floating point registers. There can be unused
         * registers see asm/hwcap.h for details.
         */
        memcpy(&ufp->fpregs, &hwstate->fpregs, sizeof(hwstate->fpregs));

        /*
         * Copy the status and control register.
         */
        ufp->fpscr = hwstate->fpscr;

        /*
         * Copy the exception registers.
         */
        ufp_exc->fpexc = hwstate->fpexc;
        ufp_exc->fpinst = hwstate->fpinst;
        ufp_exc->fpinst2 = hwstate->fpinst2;

        /* Ensure that VFP is disabled. */
        vfp_flush_hwstate(thread);

        /*
         * As per the PCS, clear the length and stride bits for function
         * entry.
         */
        hwstate->fpscr &= ~(FPSCR_LENGTH_MASK | FPSCR_STRIDE_MASK);
        return 0;
}

/* Sanitise and restore the current VFP state from the provided structures. */
int vfp_restore_user_hwstate(struct user_vfp *ufp, struct user_vfp_exc *ufp_exc)
{
        struct thread_info *thread = current_thread_info();
        struct vfp_hard_struct *hwstate = &thread->vfpstate.hard;
        unsigned long fpexc;

        /* Disable VFP to avoid corrupting the new thread state. */
        vfp_flush_hwstate(thread);

        /*
         * Copy the floating point registers. There can be unused
         * registers see asm/hwcap.h for details.
         */
        memcpy(&hwstate->fpregs, &ufp->fpregs, sizeof(hwstate->fpregs));
        /*
         * Copy the status and control register.
         */
        hwstate->fpscr = ufp->fpscr;

        /*
         * Sanitise and restore the exception registers.
         */
        fpexc = ufp_exc->fpexc;

        /* Ensure the VFP is enabled. */
        fpexc |= FPEXC_EN;

        /* Ensure FPINST2 is invalid and the exception flag is cleared. */
        fpexc &= ~(FPEXC_EX | FPEXC_FP2V);
        hwstate->fpexc = fpexc;

        hwstate->fpinst = ufp_exc->fpinst;
        hwstate->fpinst2 = ufp_exc->fpinst2;

        return 0;
}

/*
 * VFP hardware can lose all context when a CPU goes offline.
 * As we will be running in SMP mode with CPU hotplug, we will save the
 * hardware state at every thread switch.  We clear our held state when
 * a CPU has been killed, indicating that the VFP hardware doesn't contain
 * a threads VFP state.  When a CPU starts up, we re-enable access to the
 * VFP hardware. The callbacks below are called on the CPU which
 * is being offlined/onlined.
 */
static int vfp_dying_cpu(unsigned int cpu)
{
        vfp_current_hw_state[cpu] = NULL;
        return 0;
}

static int vfp_starting_cpu(unsigned int unused)
{
        vfp_enable(NULL);
        return 0;
}

void vfp_kmode_exception(void)
{
        /*
         * If we reach this point, a floating point exception has been raised
         * while running in kernel mode. If the NEON/VFP unit was enabled at the
         * time, it means a VFP instruction has been issued that requires
         * software assistance to complete, something which is not currently
         * supported in kernel mode.
         * If the NEON/VFP unit was disabled, and the location pointed to below
         * is properly preceded by a call to kernel_neon_begin(), something has
         * caused the task to be scheduled out and back in again. In this case,
         * rebuilding and running with CONFIG_DEBUG_ATOMIC_SLEEP enabled should
         * be helpful in localizing the problem.
         */
        if (fmrx(FPEXC) & FPEXC_EN)
                pr_crit("BUG: unsupported FP instruction in kernel mode\n");
        else
                pr_crit("BUG: FP instruction issued in kernel mode with FP unit disabled\n");
}

#ifdef CONFIG_KERNEL_MODE_NEON

/*
 * Kernel-side NEON support functions
 */
void kernel_neon_begin(void)
{
        struct thread_info *thread = current_thread_info();
        unsigned int cpu;
        u32 fpexc;

        /*
         * Kernel mode NEON is only allowed outside of interrupt context
         * with preemption disabled. This will make sure that the kernel
         * mode NEON register contents never need to be preserved.
         */
        BUG_ON(in_interrupt());
        cpu = get_cpu();

        fpexc = fmrx(FPEXC) | FPEXC_EN;
        fmxr(FPEXC, fpexc);

        /*
         * Save the userland NEON/VFP state. Under UP,
         * the owner could be a task other than 'current'
         */
        if (vfp_state_in_hw(cpu, thread))
                vfp_save_state(&thread->vfpstate, fpexc);
#ifndef CONFIG_SMP
        else if (vfp_current_hw_state[cpu] != NULL)
                vfp_save_state(vfp_current_hw_state[cpu], fpexc);
#endif
        vfp_current_hw_state[cpu] = NULL;
}
EXPORT_SYMBOL(kernel_neon_begin);

void kernel_neon_end(void)
{
        /* Disable the NEON/VFP unit. */
        fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
        put_cpu();
}
EXPORT_SYMBOL(kernel_neon_end);

#endif /* CONFIG_KERNEL_MODE_NEON */

/*
 * VFP support code initialisation.
 */
static int __init vfp_init(void)
{
        unsigned int vfpsid;
        unsigned int cpu_arch = cpu_architecture();

        /*
         * Enable the access to the VFP on all online CPUs so the
         * following test on FPSID will succeed.
         */
        if (cpu_arch >= CPU_ARCH_ARMv6)
                on_each_cpu(vfp_enable, NULL, 1);

        /*
         * First check that there is a VFP that we can use.
         * The handler is already setup to just log calls, so
         * we just need to read the VFPSID register.
         */
        vfp_vector = vfp_testing_entry;
        barrier();
        vfpsid = fmrx(FPSID);
        barrier();
        vfp_vector = vfp_null_entry;

        pr_info("VFP support v0.3: ");
        if (VFP_arch) {
                pr_cont("not present\n");
                return 0;
        /* Extract the architecture on CPUID scheme */
        } else if ((read_cpuid_id() & 0x000f0000) == 0x000f0000) {
                VFP_arch = vfpsid & FPSID_CPUID_ARCH_MASK;
                VFP_arch >>= FPSID_ARCH_BIT;
                /*
                 * Check for the presence of the Advanced SIMD
                 * load/store instructions, integer and single
                 * precision floating point operations. Only check
                 * for NEON if the hardware has the MVFR registers.
                 */
                if (IS_ENABLED(CONFIG_NEON) &&
                   (fmrx(MVFR1) & 0x000fff00) == 0x00011100)
                        elf_hwcap |= HWCAP_NEON;

                if (IS_ENABLED(CONFIG_VFPv3)) {
                        u32 mvfr0 = fmrx(MVFR0);
                        if (((mvfr0 & MVFR0_DP_MASK) >> MVFR0_DP_BIT) == 0x2 ||
                            ((mvfr0 & MVFR0_SP_MASK) >> MVFR0_SP_BIT) == 0x2) {
                                elf_hwcap |= HWCAP_VFPv3;
                                /*
                                 * Check for VFPv3 D16 and VFPv4 D16.  CPUs in
                                 * this configuration only have 16 x 64bit
                                 * registers.
                                 */
                                if ((mvfr0 & MVFR0_A_SIMD_MASK) == 1)
                                        /* also v4-D16 */
                                        elf_hwcap |= HWCAP_VFPv3D16;
                                else
                                        elf_hwcap |= HWCAP_VFPD32;
                        }

                        if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000)
                                elf_hwcap |= HWCAP_VFPv4;
                }
        /* Extract the architecture version on pre-cpuid scheme */
        } else {
                if (vfpsid & FPSID_NODOUBLE) {
                        pr_cont("no double precision support\n");
                        return 0;
                }

                VFP_arch = (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT;
        }

        cpuhp_setup_state_nocalls(CPUHP_AP_ARM_VFP_STARTING,
                                  "arm/vfp:starting", vfp_starting_cpu,
                                  vfp_dying_cpu);

        vfp_vector = vfp_support_entry;

        thread_register_notifier(&vfp_notifier_block);
        vfp_pm_init();

        /*
         * We detected VFP, and the support code is
         * in place; report VFP support to userspace.
         */
        elf_hwcap |= HWCAP_VFP;

        pr_cont("implementor %02x architecture %d part %02x variant %x rev %x\n",
                (vfpsid & FPSID_IMPLEMENTER_MASK) >> FPSID_IMPLEMENTER_BIT,
                VFP_arch,
                (vfpsid & FPSID_PART_MASK) >> FPSID_PART_BIT,
                (vfpsid & FPSID_VARIANT_MASK) >> FPSID_VARIANT_BIT,
                (vfpsid & FPSID_REV_MASK) >> FPSID_REV_BIT);

        return 0;
}

core_initcall(vfp_init);