/*
 *      Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
 *
 * This file contains the lowest level x86-specific interrupt
 * entry, irq-stacks and irq statistics code. All the remaining
 * irq logic is done by the generic kernel/irq/ code and
 * by the x86-specific irq controller code. (e.g. i8259.c and
 * io_apic.c.)
 */

#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/uaccess.h>
#include <linux/percpu.h>
#include <linux/mm.h>

#include <asm/apic.h>

DEFINE_PER_CPU_SHARED_ALIGNED(irq_cpustat_t, irq_stat);
EXPORT_PER_CPU_SYMBOL(irq_stat);

DEFINE_PER_CPU(struct pt_regs *, irq_regs);
EXPORT_PER_CPU_SYMBOL(irq_regs);

#ifdef CONFIG_DEBUG_STACKOVERFLOW
/* Debugging check for stack overflow: is there less than 1KB free? */
static int check_stack_overflow(void)
{
        long sp;

        __asm__ __volatile__("andl %%esp,%0" :
                             "=r" (sp) : "0" (THREAD_SIZE - 1));

        return sp < (sizeof(struct thread_info) + STACK_WARN);
}

static void print_stack_overflow(void)
{
        printk(KERN_WARNING "low stack detected by irq handler\n");
        dump_stack();
}

#else
static inline int check_stack_overflow(void) { return 0; }
static inline void print_stack_overflow(void) { }
#endif

/*
 * per-CPU IRQ handling contexts (thread information and stack)
 */
union irq_ctx {
        struct thread_info      tinfo;
        u32                     stack[THREAD_SIZE/sizeof(u32)];
} __attribute__((aligned(THREAD_SIZE)));

static DEFINE_PER_CPU(union irq_ctx *, hardirq_ctx);
static DEFINE_PER_CPU(union irq_ctx *, softirq_ctx);

static void call_on_stack(void *func, void *stack)
{
        asm volatile("xchgl     %%ebx,%%esp     \n"
                     "call      *%%edi          \n"
                     "movl      %%ebx,%%esp     \n"
                     : "=b" (stack)
                     : "0" (stack),
                       "D"(func)
                     : "memory", "cc", "edx", "ecx", "eax");
}

static inline int
execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)
{
        union irq_ctx *curctx, *irqctx;
        u32 *isp, arg1, arg2;

        curctx = (union irq_ctx *) current_thread_info();
        irqctx = __this_cpu_read(hardirq_ctx);

        /*
         * this is where we switch to the IRQ stack. However, if we are
         * already using the IRQ stack (because we interrupted a hardirq
         * handler) we can't do that and just have to keep using the
         * current stack (which is the irq stack already after all)
         */
        if (unlikely(curctx == irqctx))
                return 0;

        /* build the stack frame on the IRQ stack */
        isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));
        irqctx->tinfo.task = curctx->tinfo.task;
        irqctx->tinfo.previous_esp = current_stack_pointer;

        /*
         * Copy the softirq bits in preempt_count so that the
         * softirq checks work in the hardirq context.
         */
        irqctx->tinfo.preempt_count =
                (irqctx->tinfo.preempt_count & ~SOFTIRQ_MASK) |
                (curctx->tinfo.preempt_count & SOFTIRQ_MASK);

        if (unlikely(overflow))
                call_on_stack(print_stack_overflow, isp);

        asm volatile("xchgl     %%ebx,%%esp     \n"
                     "call      *%%edi          \n"
                     "movl      %%ebx,%%esp     \n"
                     : "=a" (arg1), "=d" (arg2), "=b" (isp)
                     :  "0" (irq),   "1" (desc),  "2" (isp),
                        "D" (desc->handle_irq)
                     : "memory", "cc", "ecx");
        return 1;
}

/*
 * allocate per-cpu stacks for hardirq and for softirq processing
 */
void __cpuinit irq_ctx_init(int cpu)
{
        union irq_ctx *irqctx;

        if (per_cpu(hardirq_ctx, cpu))
                return;

        irqctx = page_address(alloc_pages_node(cpu_to_node(cpu),
                                               THREAD_FLAGS,
                                               THREAD_ORDER));
        memset(&irqctx->tinfo, 0, sizeof(struct thread_info));
        irqctx->tinfo.cpu               = cpu;
        irqctx->tinfo.preempt_count     = HARDIRQ_OFFSET;
        irqctx->tinfo.addr_limit        = MAKE_MM_SEG(0);

        per_cpu(hardirq_ctx, cpu) = irqctx;

        irqctx = page_address(alloc_pages_node(cpu_to_node(cpu),
                                               THREAD_FLAGS,
                                               THREAD_ORDER));
        memset(&irqctx->tinfo, 0, sizeof(struct thread_info));
        irqctx->tinfo.cpu               = cpu;
        irqctx->tinfo.addr_limit        = MAKE_MM_SEG(0);

        per_cpu(softirq_ctx, cpu) = irqctx;

        printk(KERN_DEBUG "CPU %u irqstacks, hard=%p soft=%p\n",
               cpu, per_cpu(hardirq_ctx, cpu),  per_cpu(softirq_ctx, cpu));
}

asmlinkage void do_softirq(void)
{
        unsigned long flags;
        struct thread_info *curctx;
        union irq_ctx *irqctx;
        u32 *isp;

        if (in_interrupt())
                return;

        local_irq_save(flags);

        if (local_softirq_pending()) {
                curctx = current_thread_info();
                irqctx = __this_cpu_read(softirq_ctx);
                irqctx->tinfo.task = curctx->task;
                irqctx->tinfo.previous_esp = current_stack_pointer;

                /* build the stack frame on the softirq stack */
                isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));

                call_on_stack(__do_softirq, isp);
                /*
                 * Shouldn't happen, we returned above if in_interrupt():
                 */
                WARN_ON_ONCE(softirq_count());
        }

        local_irq_restore(flags);
}

bool handle_irq(unsigned irq, struct pt_regs *regs)
{
        struct irq_desc *desc;
        int overflow;

        overflow = check_stack_overflow();

        desc = irq_to_desc(irq);
        if (unlikely(!desc))
                return false;

        if (!execute_on_irq_stack(overflow, desc, irq)) {
                if (unlikely(overflow))
                        print_stack_overflow();
                desc->handle_irq(irq, desc);
        }

        return true;
}