Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1009 insertions, 0 deletions

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
new file mode 100644
index 0000000000..7e8773a2d9
--- /dev/null
+++ b/arch/arm/vfp/vfpmodule.c
@@ -0,0 +1,1009 @@
+// 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 <linux/perf_event.h>
+
+#include <asm/cp15.h>
+#include <asm/cputype.h>
+#include <asm/system_info.h>
+#include <asm/thread_notify.h>
+#include <asm/traps.h>
+#include <asm/vfp.h>
+#include <asm/neon.h>
+
+#include "vfpinstr.h"
+#include "vfp.h"
+
+static bool have_vfp __ro_after_init;
+
+/*
+ * Dual-use variable.
+ * Used in startup: set to non-zero if VFP checks fail
+ * After startup, holds VFP architecture
+ */
+static unsigned int VFP_arch;
+
+#ifdef CONFIG_CPU_FEROCEON
+extern unsigned int VFP_arch_feroceon __alias(VFP_arch);
+#endif
+
+/*
+ * 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.
+		 */
+	}
+	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
+	return exceptions & ~VFP_NAN_FLAG;
+}
+
+/*
+ * Package up a bounce condition.
+ */
+static 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) {
+		/*
+		 * Asynchronous exception. The instruction is read from FPINST
+		 * and the interrupted instruction has to be restarted.
+		 */
+		trigger = fmrx(FPINST);
+		regs->ARM_pc -= 4;
+	} 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);
+		return;
+	}
+
+	/*
+	 * 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))
+		return;
+
+	/*
+	 * 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);
+}
+
+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 __init 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();
+
+	local_bh_disable();
+
+	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);
+	}
+
+	local_bh_enable();
+	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;
+}
+
+static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr)
+{
+	/*
+	 * 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");
+	pr_crit("FPEXC == 0x%08x\n", fmrx(FPEXC));
+	return 1;
+}
+
+/*
+ * vfp_support_entry - Handle VFP exception
+ *
+ * @regs:	pt_regs structure holding the register state at exception entry
+ * @trigger:	The opcode of the instruction that triggered the exception
+ *
+ * Returns 0 if the exception was handled, or an error code otherwise.
+ */
+static int vfp_support_entry(struct pt_regs *regs, u32 trigger)
+{
+	struct thread_info *ti = current_thread_info();
+	u32 fpexc;
+
+	if (unlikely(!have_vfp))
+		return -ENODEV;
+
+	if (!user_mode(regs))
+		return vfp_kmode_exception(regs, trigger);
+
+	local_bh_disable();
+	fpexc = fmrx(FPEXC);
+
+	/*
+	 * If the VFP unit was not enabled yet, we have to check whether the
+	 * VFP state in the CPU's registers is the most recent VFP state
+	 * associated with the process. On UP systems, we don't save the VFP
+	 * state eagerly on a context switch, so we may need to save the
+	 * VFP state to memory first, as it may belong to another process.
+	 */
+	if (!(fpexc & FPEXC_EN)) {
+		/*
+		 * Enable the VFP unit but mask the FP exception flag for the
+		 * time being, so we can access all the registers.
+		 */
+		fpexc |= FPEXC_EN;
+		fmxr(FPEXC, fpexc & ~FPEXC_EX);
+
+		/*
+		 * Check whether or not the VFP state in the CPU's registers is
+		 * the most recent VFP state associated with this task. On SMP,
+		 * migration may result in multiple CPUs holding VFP states
+		 * that belong to the same task, but only the most recent one
+		 * is valid.
+		 */
+		if (!vfp_state_in_hw(ti->cpu, ti)) {
+			if (!IS_ENABLED(CONFIG_SMP) &&
+			    vfp_current_hw_state[ti->cpu] != NULL) {
+				/*
+				 * This CPU is currently holding the most
+				 * recent VFP state associated with another
+				 * task, and we must save that to memory first.
+				 */
+				vfp_save_state(vfp_current_hw_state[ti->cpu],
+					       fpexc);
+			}
+
+			/*
+			 * We can now proceed with loading the task's VFP state
+			 * from memory into the CPU registers.
+			 */
+			fpexc = vfp_load_state(&ti->vfpstate);
+			vfp_current_hw_state[ti->cpu] = &ti->vfpstate;
+#ifdef CONFIG_SMP
+			/*
+			 * Record that this CPU is now the one holding the most
+			 * recent VFP state of the task.
+			 */
+			ti->vfpstate.hard.cpu = ti->cpu;
+#endif
+		}
+
+		if (fpexc & FPEXC_EX)
+			/*
+			 * Might as well handle the pending exception before
+			 * retrying branch out before setting an FPEXC that
+			 * stops us reading stuff.
+			 */
+			goto bounce;
+
+		/*
+		 * No FP exception is pending: just enable the VFP and
+		 * replay the instruction that trapped.
+		 */
+		fmxr(FPEXC, fpexc);
+	} else {
+		/* Check for synchronous or asynchronous exceptions */
+		if (!(fpexc & (FPEXC_EX | FPEXC_DEX))) {
+			u32 fpscr = fmrx(FPSCR);
+
+			/*
+			 * On some implementations of the VFP subarch 1,
+			 * setting FPSCR.IXE causes all the CDP instructions to
+			 * be bounced synchronously without setting the
+			 * FPEXC.EX bit
+			 */
+			if (!(fpscr & FPSCR_IXE)) {
+				if (!(fpscr & FPSCR_LENGTH_MASK)) {
+					pr_debug("not VFP\n");
+					local_bh_enable();
+					return -ENOEXEC;
+				}
+				fpexc |= FPEXC_DEX;
+			}
+		}
+bounce:		regs->ARM_pc += 4;
+		VFP_bounce(trigger, fpexc, regs);
+	}
+
+	local_bh_enable();
+	return 0;
+}
+
+static struct undef_hook neon_support_hook[] = {{
+	.instr_mask	= 0xfe000000,
+	.instr_val	= 0xf2000000,
+	.cpsr_mask	= PSR_T_BIT,
+	.cpsr_val	= 0,
+	.fn		= vfp_support_entry,
+}, {
+	.instr_mask	= 0xff100000,
+	.instr_val	= 0xf4000000,
+	.cpsr_mask	= PSR_T_BIT,
+	.cpsr_val	= 0,
+	.fn		= vfp_support_entry,
+}, {
+	.instr_mask	= 0xef000000,
+	.instr_val	= 0xef000000,
+	.cpsr_mask	= PSR_T_BIT,
+	.cpsr_val	= PSR_T_BIT,
+	.fn		= vfp_support_entry,
+}, {
+	.instr_mask	= 0xff100000,
+	.instr_val	= 0xf9000000,
+	.cpsr_mask	= PSR_T_BIT,
+	.cpsr_val	= PSR_T_BIT,
+	.fn		= vfp_support_entry,
+}};
+
+static struct undef_hook vfp_support_hook = {
+	.instr_mask	= 0x0c000e00,
+	.instr_val	= 0x0c000a00,
+	.fn		= vfp_support_entry,
+};
+
+#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;
+
+	local_bh_disable();
+
+	/*
+	 * Kernel mode NEON is only allowed outside of hardirq context with
+	 * preemption and softirq processing disabled. This will make sure that
+	 * the kernel mode NEON register contents never need to be preserved.
+	 */
+	BUG_ON(in_hardirq());
+	cpu = __smp_processor_id();
+
+	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);
+	local_bh_enable();
+}
+EXPORT_SYMBOL(kernel_neon_end);
+
+#endif /* CONFIG_KERNEL_MODE_NEON */
+
+static int __init vfp_detect(struct pt_regs *regs, unsigned int instr)
+{
+	VFP_arch = UINT_MAX;	/* mark as not present */
+	regs->ARM_pc += 4;
+	return 0;
+}
+
+static struct undef_hook vfp_detect_hook __initdata = {
+	.instr_mask	= 0x0c000e00,
+	.instr_val	= 0x0c000a00,
+	.cpsr_mask	= MODE_MASK,
+	.cpsr_val	= SVC_MODE,
+	.fn		= vfp_detect,
+};
+
+/*
+ * VFP support code initialisation.
+ */
+static int __init vfp_init(void)
+{
+	unsigned int vfpsid;
+	unsigned int cpu_arch = cpu_architecture();
+	unsigned int isar6;
+
+	/*
+	 * 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.
+	 */
+	register_undef_hook(&vfp_detect_hook);
+	barrier();
+	vfpsid = fmrx(FPSID);
+	barrier();
+	unregister_undef_hook(&vfp_detect_hook);
+
+	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;
+			for (int i = 0; i < ARRAY_SIZE(neon_support_hook); i++)
+				register_undef_hook(&neon_support_hook[i]);
+		}
+
+		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;
+			if (((fmrx(MVFR1) & MVFR1_ASIMDHP_MASK) >> MVFR1_ASIMDHP_BIT) == 0x2)
+				elf_hwcap |= HWCAP_ASIMDHP;
+			if (((fmrx(MVFR1) & MVFR1_FPHP_MASK) >> MVFR1_FPHP_BIT) == 0x3)
+				elf_hwcap |= HWCAP_FPHP;
+		}
+
+		/*
+		 * Check for the presence of Advanced SIMD Dot Product
+		 * instructions.
+		 */
+		isar6 = read_cpuid_ext(CPUID_EXT_ISAR6);
+		if (cpuid_feature_extract_field(isar6, 4) == 0x1)
+			elf_hwcap |= HWCAP_ASIMDDP;
+		/*
+		 * Check for the presence of Advanced SIMD Floating point
+		 * half-precision multiplication instructions.
+		 */
+		if (cpuid_feature_extract_field(isar6, 8) == 0x1)
+			elf_hwcap |= HWCAP_ASIMDFHM;
+		/*
+		 * Check for the presence of Advanced SIMD Bfloat16
+		 * floating point instructions.
+		 */
+		if (cpuid_feature_extract_field(isar6, 20) == 0x1)
+			elf_hwcap |= HWCAP_ASIMDBF16;
+		/*
+		 * Check for the presence of Advanced SIMD and floating point
+		 * Int8 matrix multiplication instructions instructions.
+		 */
+		if (cpuid_feature_extract_field(isar6, 24) == 0x1)
+			elf_hwcap |= HWCAP_I8MM;
+
+	/* 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);
+
+	have_vfp = true;
+
+	register_undef_hook(&vfp_support_hook);
+	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);