// SPDX-License-Identifier: GPL-2.0
#include <linux/linkage.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/ioport.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/timex.h>
#include <linux/random.h>
#include <linux/init.h>
#include <linux/kernel_stat.h>
#include <linux/syscore_ops.h>
#include <linux/bitops.h>
#include <linux/acpi.h>
#include <linux/io.h>
#include <linux/delay.h>
#include <linux/pgtable.h>

#include <linux/atomic.h>
#include <asm/timer.h>
#include <asm/hw_irq.h>
#include <asm/desc.h>
#include <asm/apic.h>
#include <asm/i8259.h>
#include <asm/io_apic.h>

/*
 * This is the 'legacy' 8259A Programmable Interrupt Controller,
 * present in the majority of PC/AT boxes.
 * plus some generic x86 specific things if generic specifics makes
 * any sense at all.
 */
static void init_8259A(int auto_eoi);

static bool pcat_compat __ro_after_init;
static int i8259A_auto_eoi;
DEFINE_RAW_SPINLOCK(i8259A_lock);

/*
 * 8259A PIC functions to handle ISA devices:
 */

/*
 * This contains the irq mask for both 8259A irq controllers,
 */
unsigned int cached_irq_mask = 0xffff;

/*
 * Not all IRQs can be routed through the IO-APIC, eg. on certain (older)
 * boards the timer interrupt is not really connected to any IO-APIC pin,
 * it's fed to the master 8259A's IR0 line only.
 *
 * Any '1' bit in this mask means the IRQ is routed through the IO-APIC.
 * this 'mixed mode' IRQ handling costs nothing because it's only used
 * at IRQ setup time.
 */
unsigned long io_apic_irqs;

static void mask_8259A_irq(unsigned int irq)
{
        unsigned int mask = 1 << irq;
        unsigned long flags;

        raw_spin_lock_irqsave(&i8259A_lock, flags);
        cached_irq_mask |= mask;
        if (irq & 8)
                outb(cached_slave_mask, PIC_SLAVE_IMR);
        else
                outb(cached_master_mask, PIC_MASTER_IMR);
        raw_spin_unlock_irqrestore(&i8259A_lock, flags);
}

static void disable_8259A_irq(struct irq_data *data)
{
        mask_8259A_irq(data->irq);
}

static void unmask_8259A_irq(unsigned int irq)
{
        unsigned int mask = ~(1 << irq);
        unsigned long flags;

        raw_spin_lock_irqsave(&i8259A_lock, flags);
        cached_irq_mask &= mask;
        if (irq & 8)
                outb(cached_slave_mask, PIC_SLAVE_IMR);
        else
                outb(cached_master_mask, PIC_MASTER_IMR);
        raw_spin_unlock_irqrestore(&i8259A_lock, flags);
}

static void enable_8259A_irq(struct irq_data *data)
{
        unmask_8259A_irq(data->irq);
}

static int i8259A_irq_pending(unsigned int irq)
{
        unsigned int mask = 1<<irq;
        unsigned long flags;
        int ret;

        raw_spin_lock_irqsave(&i8259A_lock, flags);
        if (irq < 8)
                ret = inb(PIC_MASTER_CMD) & mask;
        else
                ret = inb(PIC_SLAVE_CMD) & (mask >> 8);
        raw_spin_unlock_irqrestore(&i8259A_lock, flags);

        return ret;
}

static void make_8259A_irq(unsigned int irq)
{
        disable_irq_nosync(irq);
        io_apic_irqs &= ~(1<<irq);
        irq_set_chip_and_handler(irq, &i8259A_chip, handle_level_irq);
        irq_set_status_flags(irq, IRQ_LEVEL);
        enable_irq(irq);
        lapic_assign_legacy_vector(irq, true);
}

/*
 * This function assumes to be called rarely. Switching between
 * 8259A registers is slow.
 * This has to be protected by the irq controller spinlock
 * before being called.
 */
static inline int i8259A_irq_real(unsigned int irq)
{
        int value;
        int irqmask = 1<<irq;

        if (irq < 8) {
                outb(0x0B, PIC_MASTER_CMD);     /* ISR register */
                value = inb(PIC_MASTER_CMD) & irqmask;
                outb(0x0A, PIC_MASTER_CMD);     /* back to the IRR register */
                return value;
        }
        outb(0x0B, PIC_SLAVE_CMD);      /* ISR register */
        value = inb(PIC_SLAVE_CMD) & (irqmask >> 8);
        outb(0x0A, PIC_SLAVE_CMD);      /* back to the IRR register */
        return value;
}

/*
 * Careful! The 8259A is a fragile beast, it pretty
 * much _has_ to be done exactly like this (mask it
 * first, _then_ send the EOI, and the order of EOI
 * to the two 8259s is important!
 */
static void mask_and_ack_8259A(struct irq_data *data)
{
        unsigned int irq = data->irq;
        unsigned int irqmask = 1 << irq;
        unsigned long flags;

        raw_spin_lock_irqsave(&i8259A_lock, flags);
        /*
         * Lightweight spurious IRQ detection. We do not want
         * to overdo spurious IRQ handling - it's usually a sign
         * of hardware problems, so we only do the checks we can
         * do without slowing down good hardware unnecessarily.
         *
         * Note that IRQ7 and IRQ15 (the two spurious IRQs
         * usually resulting from the 8259A-1|2 PICs) occur
         * even if the IRQ is masked in the 8259A. Thus we
         * can check spurious 8259A IRQs without doing the
         * quite slow i8259A_irq_real() call for every IRQ.
         * This does not cover 100% of spurious interrupts,
         * but should be enough to warn the user that there
         * is something bad going on ...
         */
        if (cached_irq_mask & irqmask)
                goto spurious_8259A_irq;
        cached_irq_mask |= irqmask;

handle_real_irq:
        if (irq & 8) {
                inb(PIC_SLAVE_IMR);     /* DUMMY - (do we need this?) */
                outb(cached_slave_mask, PIC_SLAVE_IMR);
                /* 'Specific EOI' to slave */
                outb(0x60+(irq&7), PIC_SLAVE_CMD);
                 /* 'Specific EOI' to master-IRQ2 */
                outb(0x60+PIC_CASCADE_IR, PIC_MASTER_CMD);
        } else {
                inb(PIC_MASTER_IMR);    /* DUMMY - (do we need this?) */
                outb(cached_master_mask, PIC_MASTER_IMR);
                outb(0x60+irq, PIC_MASTER_CMD); /* 'Specific EOI to master */
        }
        raw_spin_unlock_irqrestore(&i8259A_lock, flags);
        return;

spurious_8259A_irq:
        /*
         * this is the slow path - should happen rarely.
         */
        if (i8259A_irq_real(irq))
                /*
                 * oops, the IRQ _is_ in service according to the
                 * 8259A - not spurious, go handle it.
                 */
                goto handle_real_irq;

        {
                static int spurious_irq_mask;
                /*
                 * At this point we can be sure the IRQ is spurious,
                 * lets ACK and report it. [once per IRQ]
                 */
                if (!(spurious_irq_mask & irqmask)) {
                        printk_deferred(KERN_DEBUG
                               "spurious 8259A interrupt: IRQ%d.\n", irq);
                        spurious_irq_mask |= irqmask;
                }
                atomic_inc(&irq_err_count);
                /*
                 * Theoretically we do not have to handle this IRQ,
                 * but in Linux this does not cause problems and is
                 * simpler for us.
                 */
                goto handle_real_irq;
        }
}

struct irq_chip i8259A_chip = {
        .name           = "XT-PIC",
        .irq_mask       = disable_8259A_irq,
        .irq_disable    = disable_8259A_irq,
        .irq_unmask     = enable_8259A_irq,
        .irq_mask_ack   = mask_and_ack_8259A,
};

static char irq_trigger[2];
/* ELCR registers (0x4d0, 0x4d1) control edge/level of IRQ */
static void restore_ELCR(char *trigger)
{
        outb(trigger[0], PIC_ELCR1);
        outb(trigger[1], PIC_ELCR2);
}

static void save_ELCR(char *trigger)
{
        /* IRQ 0,1,2,8,13 are marked as reserved */
        trigger[0] = inb(PIC_ELCR1) & 0xF8;
        trigger[1] = inb(PIC_ELCR2) & 0xDE;
}

static void i8259A_resume(void *data)
{
        init_8259A(i8259A_auto_eoi);
        restore_ELCR(irq_trigger);
}

static int i8259A_suspend(void *data)
{
        save_ELCR(irq_trigger);
        return 0;
}

static void i8259A_shutdown(void *data)
{
        /* Put the i8259A into a quiescent state that
         * the kernel initialization code can get it
         * out of.
         */
        outb(0xff, PIC_MASTER_IMR);     /* mask all of 8259A-1 */
        outb(0xff, PIC_SLAVE_IMR);      /* mask all of 8259A-2 */
}

static const struct syscore_ops i8259_syscore_ops = {
        .suspend = i8259A_suspend,
        .resume = i8259A_resume,
        .shutdown = i8259A_shutdown,
};

static struct syscore i8259_syscore = {
        .ops = &i8259_syscore_ops,
};

static void mask_8259A(void)
{
        unsigned long flags;

        raw_spin_lock_irqsave(&i8259A_lock, flags);

        outb(0xff, PIC_MASTER_IMR);     /* mask all of 8259A-1 */
        outb(0xff, PIC_SLAVE_IMR);      /* mask all of 8259A-2 */

        raw_spin_unlock_irqrestore(&i8259A_lock, flags);
}

static void unmask_8259A(void)
{
        unsigned long flags;

        raw_spin_lock_irqsave(&i8259A_lock, flags);

        outb(cached_master_mask, PIC_MASTER_IMR); /* restore master IRQ mask */
        outb(cached_slave_mask, PIC_SLAVE_IMR);   /* restore slave IRQ mask */

        raw_spin_unlock_irqrestore(&i8259A_lock, flags);
}

static int probe_8259A(void)
{
        unsigned char new_val, probe_val = ~(1 << PIC_CASCADE_IR);
        unsigned long flags;

        /*
         * If MADT has the PCAT_COMPAT flag set, then do not bother probing
         * for the PIC. Some BIOSes leave the PIC uninitialized and probing
         * fails.
         *
         * Right now this causes problems as quite some code depends on
         * nr_legacy_irqs() > 0 or has_legacy_pic() == true. This is silly
         * when the system has an IO/APIC because then PIC is not required
         * at all, except for really old machines where the timer interrupt
         * must be routed through the PIC. So just pretend that the PIC is
         * there and let legacy_pic->init() initialize it for nothing.
         *
         * Alternatively this could just try to initialize the PIC and
         * repeat the probe, but for cases where there is no PIC that's
         * just pointless.
         */
        if (pcat_compat)
                return nr_legacy_irqs();

        /*
         * Check to see if we have a PIC.  Mask all except the cascade and
         * read back the value we just wrote. If we don't have a PIC, we
         * will read 0xff as opposed to the value we wrote.
         */
        raw_spin_lock_irqsave(&i8259A_lock, flags);

        outb(0xff, PIC_SLAVE_IMR);      /* mask all of 8259A-2 */
        outb(probe_val, PIC_MASTER_IMR);
        new_val = inb(PIC_MASTER_IMR);
        if (new_val != probe_val) {
                printk(KERN_INFO "Using NULL legacy PIC\n");
                legacy_pic = &null_legacy_pic;
        }

        raw_spin_unlock_irqrestore(&i8259A_lock, flags);
        return nr_legacy_irqs();
}

static void init_8259A(int auto_eoi)
{
        unsigned long flags;

        i8259A_auto_eoi = auto_eoi;

        raw_spin_lock_irqsave(&i8259A_lock, flags);

        outb(0xff, PIC_MASTER_IMR);     /* mask all of 8259A-1 */

        /*
         * outb_pic - this has to work on a wide range of PC hardware.
         */
        outb_pic(0x11, PIC_MASTER_CMD); /* ICW1: select 8259A-1 init */

        /* ICW2: 8259A-1 IR0-7 mapped to ISA_IRQ_VECTOR(0) */
        outb_pic(ISA_IRQ_VECTOR(0), PIC_MASTER_IMR);

        /* 8259A-1 (the master) has a slave on IR2 */
        outb_pic(1U << PIC_CASCADE_IR, PIC_MASTER_IMR);

        if (auto_eoi)   /* master does Auto EOI */
                outb_pic(MASTER_ICW4_DEFAULT | PIC_ICW4_AEOI, PIC_MASTER_IMR);
        else            /* master expects normal EOI */
                outb_pic(MASTER_ICW4_DEFAULT, PIC_MASTER_IMR);

        outb_pic(0x11, PIC_SLAVE_CMD);  /* ICW1: select 8259A-2 init */

        /* ICW2: 8259A-2 IR0-7 mapped to ISA_IRQ_VECTOR(8) */
        outb_pic(ISA_IRQ_VECTOR(8), PIC_SLAVE_IMR);
        /* 8259A-2 is a slave on master's IR2 */
        outb_pic(PIC_CASCADE_IR, PIC_SLAVE_IMR);
        /* (slave's support for AEOI in flat mode is to be investigated) */
        outb_pic(SLAVE_ICW4_DEFAULT, PIC_SLAVE_IMR);

        if (auto_eoi)
                /*
                 * In AEOI mode we just have to mask the interrupt
                 * when acking.
                 */
                i8259A_chip.irq_mask_ack = disable_8259A_irq;
        else
                i8259A_chip.irq_mask_ack = mask_and_ack_8259A;

        udelay(100);            /* wait for 8259A to initialize */

        outb(cached_master_mask, PIC_MASTER_IMR); /* restore master IRQ mask */
        outb(cached_slave_mask, PIC_SLAVE_IMR);   /* restore slave IRQ mask */

        raw_spin_unlock_irqrestore(&i8259A_lock, flags);
}

/*
 * make i8259 a driver so that we can select pic functions at run time. the goal
 * is to make x86 binary compatible among pc compatible and non-pc compatible
 * platforms, such as x86 MID.
 */

static void legacy_pic_noop(void) { };
static void legacy_pic_uint_noop(unsigned int unused) { };
static void legacy_pic_int_noop(int unused) { };
static int legacy_pic_irq_pending_noop(unsigned int irq)
{
        return 0;
}
static int legacy_pic_probe(void)
{
        return 0;
}

struct legacy_pic null_legacy_pic = {
        .nr_legacy_irqs = 0,
        .chip = &dummy_irq_chip,
        .mask = legacy_pic_uint_noop,
        .unmask = legacy_pic_uint_noop,
        .mask_all = legacy_pic_noop,
        .restore_mask = legacy_pic_noop,
        .init = legacy_pic_int_noop,
        .probe = legacy_pic_probe,
        .irq_pending = legacy_pic_irq_pending_noop,
        .make_irq = legacy_pic_uint_noop,
};

static struct legacy_pic default_legacy_pic = {
        .nr_legacy_irqs = NR_IRQS_LEGACY,
        .chip  = &i8259A_chip,
        .mask = mask_8259A_irq,
        .unmask = unmask_8259A_irq,
        .mask_all = mask_8259A,
        .restore_mask = unmask_8259A,
        .init = init_8259A,
        .probe = probe_8259A,
        .irq_pending = i8259A_irq_pending,
        .make_irq = make_8259A_irq,
};

struct legacy_pic *legacy_pic = &default_legacy_pic;
EXPORT_SYMBOL(legacy_pic);

static int __init i8259A_init_ops(void)
{
        if (legacy_pic == &default_legacy_pic)
                register_syscore(&i8259_syscore);

        return 0;
}
device_initcall(i8259A_init_ops);

void __init legacy_pic_pcat_compat(void)
{
        pcat_compat = true;
}