arch/arm/vfp/vfpmodule.c - kernel/panda - Git at Google

 /*
  *  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/kernel.h>
 #include <linux/notifier.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/smp.h>
 #include <linux/init.h>

 #include <asm/cputype.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;

 /*
  * 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.
  */
 union vfp_state *vfp_current_hw_state[NR_CPUS];

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

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

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

 	vfp->hard.fpexc = FPEXC_EN;
 	vfp->hard.fpscr = FPSCR_ROUND_NEAREST;

 	/*
 	 * 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.
 	 */
 	cpu = get_cpu();
 	if (vfp_current_hw_state[cpu] == vfp)
 		vfp_current_hw_state[cpu] = NULL;
 	fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
 	put_cpu();
 }

 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;
 }

 /*
  * 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);
 			vfp_current_hw_state[cpu]->hard.cpu = cpu;
 		}
 		/*
 		 * Thread migration, just force the reloading of the
 		 * state on the new CPU in case the VFP registers
 		 * contain stale data.
 		 */
 		if (thread->vfpstate.hard.cpu != cpu)
 			vfp_current_hw_state[cpu] = NULL;
 #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;

 	printk(KERN_ERR "VFP: Error: %s\n", reason);
 	printk(KERN_ERR "VFP: EXC 0x%08x SCR 0x%08x INST 0x%08x\n",
 		fmrx(FPEXC), fmrx(FPSCR), inst);
 	for (i = 0; i < 32; i += 2)
 		printk(KERN_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 = 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) {
 		printk(KERN_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]) {
 		fmxr(FPEXC, fpexc | FPEXC_EN);
 		vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
 		fmxr(FPEXC, fpexc);
 	}

 	/* clear any information we had about last context state */
 	memset(vfp_current_hw_state, 0, sizeof(vfp_current_hw_state));

 	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 */

 void vfp_sync_hwstate(struct thread_info *thread)
 {
 	unsigned int cpu = get_cpu();

 	/*
 	 * If the thread we're interested in is the current owner of the
 	 * hardware VFP state, then we need to save its state.
 	 */
 	if (vfp_current_hw_state[cpu] == &thread->vfpstate) {
 		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();
 }

 void vfp_flush_hwstate(struct thread_info *thread)
 {
 	unsigned int cpu = get_cpu();

 	/*
 	 * If the thread we're interested in is the current owner of the
 	 * hardware VFP state, then we need to save its state.
 	 */
 	if (vfp_current_hw_state[cpu] == &thread->vfpstate) {
 		u32 fpexc = fmrx(FPEXC);

 		fmxr(FPEXC, fpexc & ~FPEXC_EN);

 		/*
 		 * Set the context to NULL to force a reload the next time
 		 * the thread uses the VFP.
 		 */
 		vfp_current_hw_state[cpu] = NULL;
 	}

 #ifdef CONFIG_SMP
 	/*
 	 * For SMP we still have to take care of the case where the thread
 	 * migrates to another CPU and then back to the original CPU on which
 	 * the last VFP user is still the same thread. Mark the thread VFP
 	 * state as belonging to a non-existent CPU so that the saved one will
 	 * be reloaded in the above case.
 	 */
 	thread->vfpstate.hard.cpu = NR_CPUS;
 #endif
 	put_cpu();
 }

 /*
  * 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) {
 		unsigned int cpu = (long)hcpu;
 		vfp_current_hw_state[cpu] = NULL;
 	} 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)
 		vfp_enable(NULL);

 	/*
 	 * 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;

 	printk(KERN_INFO "VFP support v0.3: ");
 	if (VFP_arch)
 		printk("not present\n");
 	else if (vfpsid & FPSID_NODOUBLE) {
 		printk("no double precision support\n");
 	} else {
 		hotcpu_notifier(vfp_hotplug, 0);

 		smp_call_function(vfp_enable, NULL, 1);

 		VFP_arch = (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT;  /* Extract the architecture version */
 		printk("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. CPUs in this configuration
 			 * only have 16 x 64bit registers.
 			 */
 			if (((fmrx(MVFR0) & MVFR0_A_SIMD_MASK)) == 1)
 				elf_hwcap |= HWCAP_VFPv3D16;
 		}
 #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
 			if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000)
 				elf_hwcap |= HWCAP_VFPv4;
 		}
 	}
 	return 0;
 }

 late_initcall(vfp_init);
	/*
	* 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/kernel.h>
	#include <linux/notifier.h>
	#include <linux/signal.h>
	#include <linux/sched.h>
	#include <linux/smp.h>
	#include <linux/init.h>

	#include <asm/cputype.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;

	/*
	* 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.
	*/
	union vfp_state *vfp_current_hw_state[NR_CPUS];

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

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

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

	vfp->hard.fpexc = FPEXC_EN;
	vfp->hard.fpscr = FPSCR_ROUND_NEAREST;

	/*
	* 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.
	*/
	cpu = get_cpu();
	if (vfp_current_hw_state[cpu] == vfp)
	vfp_current_hw_state[cpu] = NULL;
	fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
	put_cpu();
	}

	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;
	}

	/*
	* 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);
	vfp_current_hw_state[cpu]->hard.cpu = cpu;
	}
	/*
	* Thread migration, just force the reloading of the
	* state on the new CPU in case the VFP registers
	* contain stale data.
	*/
	if (thread->vfpstate.hard.cpu != cpu)
	vfp_current_hw_state[cpu] = NULL;
	#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;

	printk(KERN_ERR "VFP: Error: %s\n", reason);
	printk(KERN_ERR "VFP: EXC 0x%08x SCR 0x%08x INST 0x%08x\n",
	fmrx(FPEXC), fmrx(FPSCR), inst);
	for (i = 0; i < 32; i += 2)
	printk(KERN_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 = 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) {
	printk(KERN_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]) {
	fmxr(FPEXC, fpexc \| FPEXC_EN);
	vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
	fmxr(FPEXC, fpexc);
	}

	/* clear any information we had about last context state */
	memset(vfp_current_hw_state, 0, sizeof(vfp_current_hw_state));

	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 */

	void vfp_sync_hwstate(struct thread_info *thread)
	{
	unsigned int cpu = get_cpu();

	/*
	* If the thread we're interested in is the current owner of the
	* hardware VFP state, then we need to save its state.
	*/
	if (vfp_current_hw_state[cpu] == &thread->vfpstate) {
	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();
	}

	void vfp_flush_hwstate(struct thread_info *thread)
	{
	unsigned int cpu = get_cpu();

	/*
	* If the thread we're interested in is the current owner of the
	* hardware VFP state, then we need to save its state.
	*/
	if (vfp_current_hw_state[cpu] == &thread->vfpstate) {
	u32 fpexc = fmrx(FPEXC);

	fmxr(FPEXC, fpexc & ~FPEXC_EN);

	/*
	* Set the context to NULL to force a reload the next time
	* the thread uses the VFP.
	*/
	vfp_current_hw_state[cpu] = NULL;
	}

	#ifdef CONFIG_SMP
	/*
	* For SMP we still have to take care of the case where the thread
	* migrates to another CPU and then back to the original CPU on which
	* the last VFP user is still the same thread. Mark the thread VFP
	* state as belonging to a non-existent CPU so that the saved one will
	* be reloaded in the above case.
	*/
	thread->vfpstate.hard.cpu = NR_CPUS;
	#endif
	put_cpu();
	}

	/*
	* 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) {
	unsigned int cpu = (long)hcpu;
	vfp_current_hw_state[cpu] = NULL;
	} 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)
	vfp_enable(NULL);

	/*
	* 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;

	printk(KERN_INFO "VFP support v0.3: ");
	if (VFP_arch)
	printk("not present\n");
	else if (vfpsid & FPSID_NODOUBLE) {
	printk("no double precision support\n");
	} else {
	hotcpu_notifier(vfp_hotplug, 0);

	smp_call_function(vfp_enable, NULL, 1);

	VFP_arch = (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT; /* Extract the architecture version */
	printk("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. CPUs in this configuration
	* only have 16 x 64bit registers.
	*/
	if (((fmrx(MVFR0) & MVFR0_A_SIMD_MASK)) == 1)
	elf_hwcap \|= HWCAP_VFPv3D16;
	}
	#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
	if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000)
	elf_hwcap \|= HWCAP_VFPv4;
	}
	}
	return 0;
	}

	late_initcall(vfp_init);