vfpmodule.c

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/*
 *  linux/arch/arm/vfp/vfpmodule.c
 *
 *  Copyright (C) 2004 ARM Limited.
 *  Written by Deep Blue Solutions Limited.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#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.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/uaccess.h>
#include <linux/user.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)
 */
void vfp_testing_entry(void);
void vfp_support_entry(void);
void vfp_null_entry(void);

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
 *   - 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.
 */
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)
{
    siginfo_t info;

    memset(&info, 0, sizeof(info));

    info.si_signo = SIGFPE;
    info.si_code = sicode;
    info.si_addr = (void __user *)(instruction_pointer(regs) - 4);

    /*
     * 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_info(SIGFPE, &info, 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(0, 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))
        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));
}

#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 __user *ufp,
                    struct user_vfp_exc __user *ufp_exc)
{
    struct thread_info *thread = current_thread_info();
    struct vfp_hard_struct *hwstate = &thread->vfpstate.hard;
    int err = 0;

    /* 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.
     */
    err |= __copy_to_user(&ufp->fpregs, &hwstate->fpregs,
                  sizeof(hwstate->fpregs));
    /*
     * Copy the status and control register.
     */
    __put_user_error(hwstate->fpscr, &ufp->fpscr, err);

    /*
     * Copy the exception registers.
     */
    __put_user_error(hwstate->fpexc, &ufp_exc->fpexc, err);
    __put_user_error(hwstate->fpinst, &ufp_exc->fpinst, err);
    __put_user_error(hwstate->fpinst2, &ufp_exc->fpinst2, err);

    if (err)
        return -EFAULT;

    /* 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 __user *ufp,
                 struct user_vfp_exc __user *ufp_exc)
{
    struct thread_info *thread = current_thread_info();
    struct vfp_hard_struct *hwstate = &thread->vfpstate.hard;
    unsigned long fpexc;
    int err = 0;

    /* 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.
     */
    err |= __copy_from_user(&hwstate->fpregs, &ufp->fpregs,
                sizeof(hwstate->fpregs));
    /*
     * Copy the status and control register.
     */
    __get_user_error(hwstate->fpscr, &ufp->fpscr, err);

    /*
     * Sanitise and restore the exception registers.
     */
    __get_user_error(fpexc, &ufp_exc->fpexc, err);

    /* 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;

    __get_user_error(hwstate->fpinst, &ufp_exc->fpinst, err);
    __get_user_error(hwstate->fpinst2, &ufp_exc->fpinst2, err);

    return err ? -EFAULT : 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.
 *
 * Both CPU_DYING and CPU_STARTING are called on the CPU which
 * is being offlined/onlined.
 */
static int vfp_hotplug(struct notifier_block *b, unsigned long action,
    void *hcpu)
{
    if (action == CPU_DYING || action == CPU_DYING_FROZEN) {
        vfp_force_reload((long)hcpu, current_thread_info());
    } else if (action == CPU_STARTING || action == CPU_STARTING_FROZEN)
        vfp_enable(NULL);
    return NOTIFY_OK;
}

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

    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");
    else if (vfpsid & FPSID_NODOUBLE) {
        pr_cont("no double precision support\n");
    } else {
        hotcpu_notifier(vfp_hotplug, 0);

        VFP_arch = (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT;  /* Extract the architecture version */
        pr_cont("implementor %02x architecture %d part %02x variant %x rev %x\n",
            (vfpsid & FPSID_IMPLEMENTER_MASK) >> FPSID_IMPLEMENTER_BIT,
            (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT,
            (vfpsid & FPSID_PART_MASK) >> FPSID_PART_BIT,
            (vfpsid & FPSID_VARIANT_MASK) >> FPSID_VARIANT_BIT,
            (vfpsid & FPSID_REV_MASK) >> FPSID_REV_BIT);

        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;
#ifdef CONFIG_VFPv3
        if (VFP_arch >= 2) {
            elf_hwcap |= HWCAP_VFPv3;

            /*
             * Check for VFPv3 D16 and VFPv4 D16.  CPUs in
             * this configuration only have 16 x 64bit
             * registers.
             */
            if (((fmrx(MVFR0) & MVFR0_A_SIMD_MASK)) == 1)
                elf_hwcap |= HWCAP_VFPv3D16; /* also v4-D16 */
            else
                elf_hwcap |= HWCAP_VFPD32;
        }
#endif
        /*
         * 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 ((read_cpuid_id() & 0x000f0000) == 0x000f0000) {
#ifdef CONFIG_NEON
            if ((fmrx(MVFR1) & 0x000fff00) == 0x00011100)
                elf_hwcap |= HWCAP_NEON;
#endif
#ifdef CONFIG_VFPv3
            if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000)
                elf_hwcap |= HWCAP_VFPv4;
#endif
        }
    }
    return 0;
}

late_initcall(vfp_init);