nt-lite/code/kernel/ke_irq.c

// ke_irq.c - IRQ dispatch, kernel-side
#include <kernel/ke_irq.h>
#include <kernel/ke_sched.h>
#include <kernel/ke_cpu.h>
#include <kernel/ke_idt.h>
#include <kernel/ke_irql.h>
#include <kernel/ke_dpc.h>
#include <ntlite/ddi/hal_api.h>
#include <kernel/ke_debug.h>

#define MAX_IRQS 24
#define MAX_IRQ_HANDLERS 8

typedef struct IRQ_HANDLER_LIST {
    void (*Handlers[MAX_IRQ_HANDLERS])(void);
    uint8_t Count;
} IRQ_HANDLER_LIST;

static IRQ_HANDLER_LIST gIrqHandlers[MAX_IRQS];
static const HAL_API *gHal;

static KIRQL KiIrqToIrql(uint8_t irq) {
    uint32_t level = (uint32_t)DIRQL_BASE + (uint32_t)irq;
    if (level >= HIGH_LEVEL)
        level = (uint32_t)(HIGH_LEVEL - 1);
    return (KIRQL)level;
}

void KeIrqInitialize(const HAL_API *hal) {
    gHal = hal;
}

__declspec(dllexport) void KeIrqRegister(uint8_t irq, void (*handler)(void)) {
    if (irq >= MAX_IRQS || !handler) return;

    IRQ_HANDLER_LIST* list = &gIrqHandlers[irq];
    for (uint8_t i = 0; i < list->Count; i++) {
        if (list->Handlers[i] == handler)
            return;
    }

    if (list->Count >= MAX_IRQ_HANDLERS) {
        DbgPrint("KeIrqRegister: IRQ %u handler table full\n", irq);
        return;
    }

    list->Handlers[list->Count++] = handler;
    gHal->Intc.RouteIrq(irq);
}

void KeIrqDispatch(uint8_t irq) {
    KIRQL targetIrql = KiIrqToIrql(irq);
    KIRQL currentIrql = KeGetCurrentIrql();

    // Do not ever lower IRQL on interrupt entry. Nested IRQs are not expected
    // while IF is clear, but preserving monotonic IRQL keeps nesting safe.
    if (targetIrql < currentIrql)
        targetIrql = currentIrql;

    KIRQL oldIrql = KeRaiseIrql(targetIrql);

    if (irq == KE_VECTOR_RESCHEDULE_IPI) {
        // Nothing to do here. The sender has already set this CPU's
        // ReschedulePending flag. KiExitInterrupt consumes it after EOI and
        // after the interrupted frame unwinds to PASSIVE_LEVEL.
    } else if (irq < MAX_IRQS) {
        IRQ_HANDLER_LIST* list = &gIrqHandlers[irq];
        for (uint8_t i = 0; i < list->Count; i++) {
            if (list->Handlers[i])
                list->Handlers[i]();
        }
    }

    // Handlers are no longer allowed to context-switch directly.  Timer IRQs
    // only request rescheduling; KiExitInterrupt performs the switch after this
    // function returns, so the EOI is guaranteed to be sent first.  Keep the
    // software level at DIRQL until after the controller has been acknowledged.
    gHal->Intc.SendEoi();

    KeLowerIrql(oldIrql);
}

void KiEnterInterrupt(void) {
    KeGetCurrentCpu()->InterruptDepth++;
}

void KiExitInterrupt(void) {
    KCPU* cpu = KeGetCurrentCpu();
    if (cpu->InterruptDepth)
        cpu->InterruptDepth--;

    // A reschedule is only legal after the interrupt unwinds back to the
    // interrupted thread's PASSIVE context. If an interrupt hit DISPATCH/DIRQL
    // code, leave the request pending instead of switching out of a spinlock or
    // high-IRQL region.
    if (cpu->InterruptDepth == 0 && KeGetCurrentIrql() == PASSIVE_LEVEL) {
        KiDrainDpcQueue();
        if (KeGetCurrentIrql() == PASSIVE_LEVEL)
            KiScheduleFromInterrupt();
    }
}