nt-lite/code/drivers/rtl8139/rtl8139.c

// rtl8139.c - Realtek RTL8139 / QEMU rtl8139 PCI fast Ethernet driver.
//
// Scope for this first version:
//   * PCI ID 10ec:8139, legacy INTx interrupts.
//   * MMIO preferred, I/O BAR fallback.
//   * Classic RTL8139 register interface: one RX ring buffer and four TX slots.
//   * No checksum offload, C+ mode, VLAN, multicast hash programming, or power mgmt.
//
// This is intentionally a separate mini-driver from rtl816x.sys.  RTL8139 and
// RTL8111/8168 share a vendor but not a useful packet-DMA programming model.

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>
#include <string.h>
#include <intrin.h>

#include <hal_api.h>
#include <ke_status.h>
#include <ke_debug.h>
#include <ke_irq.h>
#include <ke_dpc.h>
#include <ke_spinlock.h>
#include <mm_phys.h>
#include <mm_virt.h>
#include <net_device.h>

#define RTL8139_VENDOR_REALTEK 0x10ECu
#define RTL8139_DEVICE_ID      0x8139u

#define PCI_REG_COMMAND        0x04u
#define PCI_REG_BAR0           0x10u
#define PCI_COMMAND_IO         (1u << 0)
#define PCI_COMMAND_MEMORY     (1u << 1)
#define PCI_COMMAND_MASTER     (1u << 2)
#define PCI_COMMAND_INTX_DISABLE (1u << 10)

#define RTL8139_REG_IDR0       0x00u
#define RTL8139_REG_MAR0       0x08u
#define RTL8139_REG_TSD0       0x10u
#define RTL8139_REG_TSAD0      0x20u
#define RTL8139_REG_RBSTART    0x30u
#define RTL8139_REG_CMD        0x37u
#define RTL8139_REG_CAPR       0x38u
#define RTL8139_REG_CBR        0x3Au
#define RTL8139_REG_IMR        0x3Cu
#define RTL8139_REG_ISR        0x3Eu
#define RTL8139_REG_TCR        0x40u
#define RTL8139_REG_RCR        0x44u
#define RTL8139_REG_CONFIG1    0x52u

#define RTL8139_CMD_BUFE       0x01u
#define RTL8139_CMD_TE         0x04u
#define RTL8139_CMD_RE         0x08u
#define RTL8139_CMD_RST        0x10u

#define RTL8139_ISR_ROK        0x0001u
#define RTL8139_ISR_RER        0x0002u
#define RTL8139_ISR_TOK        0x0004u
#define RTL8139_ISR_TER        0x0008u
#define RTL8139_ISR_RXOVW      0x0010u
#define RTL8139_ISR_PUN        0x0020u
#define RTL8139_ISR_FOVW       0x0040u
#define RTL8139_ISR_LENCHG     0x2000u
#define RTL8139_ISR_TIMEOUT    0x4000u
#define RTL8139_ISR_SYSERR     0x8000u

#define RTL8139_INTR_ENABLES   (RTL8139_ISR_ROK | RTL8139_ISR_RER | RTL8139_ISR_TOK | \
                                RTL8139_ISR_TER | RTL8139_ISR_RXOVW | RTL8139_ISR_PUN | \
                                RTL8139_ISR_FOVW | RTL8139_ISR_LENCHG | RTL8139_ISR_SYSERR)

#define RTL8139_RCR_AAP        (1u << 0)
#define RTL8139_RCR_APM        (1u << 1)
#define RTL8139_RCR_AM         (1u << 2)
#define RTL8139_RCR_AB         (1u << 3)
#define RTL8139_RCR_AR         (1u << 4)
#define RTL8139_RCR_AER        (1u << 5)
#define RTL8139_RCR_WRAP       (1u << 7)
#define RTL8139_RCR_MXDMA_UNLIMITED (7u << 8)
#define RTL8139_RCR_RBLEN_8K   (0u << 11)

#define RTL8139_TCR_MXDMA_UNLIMITED (7u << 8)
#define RTL8139_TCR_IFG_NORMAL      (3u << 24)

#define RTL8139_TSD_SIZE_MASK  0x00001FFFu
#define RTL8139_TSD_OWN        (1u << 13)
#define RTL8139_TSD_TUN        (1u << 14)
#define RTL8139_TSD_TOK        (1u << 15)
#define RTL8139_TSD_TABT       (1u << 30)

#define RTL8139_RX_OK          0x0001u
#define RTL8139_RX_BAD_BITS    0x003Eu // FAE | CRC | LONG | RUNT | ISE; MAR/PAM/BAR are valid match flags.

#define RTL8139_TX_SLOTS       4u
#define RTL8139_TX_BUF_SIZE    2048u
#define RTL8139_RX_RING_SIZE   8192u
#define RTL8139_RX_PAD         16u
#define RTL8139_RX_GUARD       1500u
#define RTL8139_RX_ALLOC_SIZE  (RTL8139_RX_RING_SIZE + RTL8139_RX_PAD + RTL8139_RX_GUARD)
#define RTL8139_RX_PAGES       ((RTL8139_RX_ALLOC_SIZE + 4095u) / 4096u)
#define RTL8139_TX_PAGES       (((RTL8139_TX_SLOTS * RTL8139_TX_BUF_SIZE) + 4095u) / 4096u)
#define RTL8139_MMIO_PAGES     1u
#define RTL8139_RX_WIRE_MAX   (NET_ETHERNET_MAX_FRAME + 4u)

#define RTL8139_REG_TSD(slot)  (RTL8139_REG_TSD0 + ((slot) * 4u))
#define RTL8139_REG_TSAD(slot) (RTL8139_REG_TSAD0 + ((slot) * 4u))

typedef enum RTL8139_BAR_KIND {
    Rtl8139BarNone = 0,
    Rtl8139BarIo,
    Rtl8139BarMmio,
} RTL8139_BAR_KIND;

typedef struct RTL8139_BAR {
    RTL8139_BAR_KIND Kind;
    uint64_t         Base;
    uint8_t          Index;
} RTL8139_BAR;

typedef struct RTL8139_DEVICE {
    uint8_t Bus;
    uint8_t Dev;
    uint8_t Fn;
    uint8_t Irq;

    bool UseMmio;
    volatile uint8_t* Mmio;
    uint16_t IoBase;

    PHYSICAL_ADDRESS RxPhys;
    PHYSICAL_ADDRESS TxPhys;
    uint8_t* RxBuffer;
    uint8_t* TxBuffers;
    uint8_t  RxScratch[RTL8139_TX_BUF_SIZE];

    uint32_t RxOffset;
    uint32_t TxSlot;
    SPINLOCK TxLock;
    KDPC Dpc;
    volatile uint16_t PendingIsr;

    NET_DEVICE NetDevice;
} RTL8139_DEVICE;

static const HAL_API* gHal;
static RTL8139_DEVICE gDevice;
static bool gDevicePresent = false;

static __forceinline void Rtl8139MemoryBarrier(void) {
    _ReadWriteBarrier();
    _mm_mfence();
    _ReadWriteBarrier();
}

static uint8_t Rtl8139Read8(RTL8139_DEVICE* r, uint32_t reg) {
    if (r->UseMmio)
        return *(volatile uint8_t*)(r->Mmio + reg);
    return __inbyte((unsigned short)(r->IoBase + reg));
}

static uint16_t Rtl8139Read16(RTL8139_DEVICE* r, uint32_t reg) {
    if (r->UseMmio)
        return *(volatile uint16_t*)(r->Mmio + reg);
    return __inword((unsigned short)(r->IoBase + reg));
}

static uint32_t Rtl8139Read32(RTL8139_DEVICE* r, uint32_t reg) {
    if (r->UseMmio)
        return *(volatile uint32_t*)(r->Mmio + reg);
    return __indword((unsigned short)(r->IoBase + reg));
}

static void Rtl8139Write8(RTL8139_DEVICE* r, uint32_t reg, uint8_t value) {
    if (r->UseMmio) *(volatile uint8_t*)(r->Mmio + reg) = value;
    else __outbyte((unsigned short)(r->IoBase + reg), value);
}

static void Rtl8139Write16(RTL8139_DEVICE* r, uint32_t reg, uint16_t value) {
    if (r->UseMmio) *(volatile uint16_t*)(r->Mmio + reg) = value;
    else __outword((unsigned short)(r->IoBase + reg), value);
}

static void Rtl8139Write32(RTL8139_DEVICE* r, uint32_t reg, uint32_t value) {
    if (r->UseMmio) *(volatile uint32_t*)(r->Mmio + reg) = value;
    else __outdword((unsigned short)(r->IoBase + reg), value);
}

static bool Rtl8139ReadBar(uint8_t bus, uint8_t dev, uint8_t fn, uint8_t index, RTL8139_BAR* out) {
    uint8_t reg = (uint8_t)(PCI_REG_BAR0 + index * 4u);
    uint32_t lo = gHal->Pci.Read32(bus, dev, fn, reg);

    out->Kind = Rtl8139BarNone;
    out->Base = 0;
    out->Index = index;

    if (lo == 0 || lo == 0xFFFFFFFFu)
        return false;

    if (lo & 1u) {
        uint32_t base = lo & ~0x3u;
        if (!base) return false;
        out->Kind = Rtl8139BarIo;
        out->Base = base;
        return true;
    }

    uint64_t base = (uint64_t)(lo & ~0xFu);
    uint32_t type = (lo >> 1) & 0x3u;
    if (type == 0x2u && index < 5) {
        uint32_t hi = gHal->Pci.Read32(bus, dev, fn, (uint8_t)(reg + 4u));
        base |= ((uint64_t)hi << 32);
    }

    if (!base) return false;
    out->Kind = Rtl8139BarMmio;
    out->Base = base;
    return true;
}

static KSTATUS Rtl8139MapMmio(uint64_t physBase, volatile uint8_t** outMmio) {
    uint64_t pageBase = physBase & PAGE_MASK;
    uint64_t pageOff  = physBase - pageBase;

    for (uint32_t i = 0; i < RTL8139_MMIO_PAGES; i++) {
        PHYSICAL_ADDRESS phys = pageBase + (uint64_t)i * PAGE_SIZE;
        uintptr_t virt = (uintptr_t)gHal->PhysToVirt(phys);
        KSTATUS st = MmMapPage(virt, phys, PAGE_PRESENT | PAGE_WRITE | PAGE_NOCACHE);
        if (st == STATUS_ALREADY_EXISTS)
            st = MmSetPageProtect(virt, PAGE_SIZE, PAGE_PRESENT | PAGE_WRITE | PAGE_NOCACHE);
        if (!KSUCCESS(st))
            return st;
    }

    *outMmio = (volatile uint8_t*)((uintptr_t)gHal->PhysToVirt(pageBase) + pageOff);
    return STATUS_SUCCESS;
}

static KSTATUS Rtl8139SelectRegisterBar(RTL8139_DEVICE* r) {
    RTL8139_BAR best = { Rtl8139BarNone, 0, 0 };
    RTL8139_BAR fallback = { Rtl8139BarNone, 0, 0 };

    for (uint8_t i = 0; i < 6; i++) {
        RTL8139_BAR bar;
        if (!Rtl8139ReadBar(r->Bus, r->Dev, r->Fn, i, &bar))
            continue;

        if (bar.Kind == Rtl8139BarMmio) {
            best = bar;
            break;
        }
        if (bar.Kind == Rtl8139BarIo && fallback.Kind == Rtl8139BarNone)
            fallback = bar;

        if (bar.Kind == Rtl8139BarMmio) {
            uint32_t lo = gHal->Pci.Read32(r->Bus, r->Dev, r->Fn, (uint8_t)(PCI_REG_BAR0 + i * 4u));
            if (((lo >> 1) & 0x3u) == 0x2u)
                i++;
        }
    }

    if (best.Kind == Rtl8139BarNone)
        best = fallback;

    if (best.Kind == Rtl8139BarMmio) {
        KSTATUS st = Rtl8139MapMmio(best.Base, &r->Mmio);
        if (!KSUCCESS(st))
            return st;
        r->UseMmio = true;
        DbgPrint("RTL8139: BAR%u MMIO base=0x%llx virt=%p\n",
                 best.Index, (unsigned long long)best.Base, r->Mmio);
        return STATUS_SUCCESS;
    }

    if (best.Kind == Rtl8139BarIo) {
        if (best.Base > 0xFFFFu)
            return STATUS_NOT_SUPPORTED;
        r->IoBase = (uint16_t)best.Base;
        r->UseMmio = false;
        DbgPrint("RTL8139: BAR%u I/O base=0x%04x\n", best.Index, r->IoBase);
        return STATUS_SUCCESS;
    }

    return STATUS_NOT_FOUND;
}

static void Rtl8139EnablePci(RTL8139_DEVICE* r) {
    uint32_t cmd = gHal->Pci.Read32(r->Bus, r->Dev, r->Fn, PCI_REG_COMMAND);
    cmd |= PCI_COMMAND_MASTER;
    if (r->UseMmio) cmd |= PCI_COMMAND_MEMORY;
    else            cmd |= PCI_COMMAND_IO;
    cmd &= ~PCI_COMMAND_INTX_DISABLE;
    gHal->Pci.Write32(r->Bus, r->Dev, r->Fn, PCI_REG_COMMAND, cmd);
}

static KSTATUS Rtl8139Reset(RTL8139_DEVICE* r) {
    Rtl8139Write8(r, RTL8139_REG_CMD, RTL8139_CMD_RST);
    for (uint32_t i = 0; i < 1000; i++) {
        if ((Rtl8139Read8(r, RTL8139_REG_CMD) & RTL8139_CMD_RST) == 0)
            return STATUS_SUCCESS;
        if (gHal->Timer.Stall)
            gHal->Timer.Stall(1000);
    }
    return STATUS_TIMEOUT;
}

static void Rtl8139ReadMac(RTL8139_DEVICE* r) {
    for (uint32_t i = 0; i < 6; i++)
        r->NetDevice.HardwareAddress[i] = Rtl8139Read8(r, RTL8139_REG_IDR0 + i);
    r->NetDevice.HardwareAddressLength = 6;
}

static KSTATUS Rtl8139AllocateDma(RTL8139_DEVICE* r) {
    r->RxPhys = MmAllocateContiguous(RTL8139_RX_PAGES);
    r->TxPhys = MmAllocateContiguous(RTL8139_TX_PAGES);
    if (!r->RxPhys || !r->TxPhys)
        return STATUS_NO_MEMORY;

    // RTL8139 has 32-bit DMA address registers.  This is fine for typical QEMU
    // and low-memory hobby OS configs, but make failure explicit.
    if ((r->RxPhys + RTL8139_RX_ALLOC_SIZE - 1) > 0xFFFFFFFFULL ||
        (r->TxPhys + RTL8139_TX_SLOTS * RTL8139_TX_BUF_SIZE - 1) > 0xFFFFFFFFULL) {
        DbgPrint("RTL8139: DMA allocation above 4GiB is not supported by this NIC\n");
        return STATUS_NOT_SUPPORTED;
    }

    r->RxBuffer = (uint8_t*)gHal->PhysToVirt(r->RxPhys);
    r->TxBuffers = (uint8_t*)gHal->PhysToVirt(r->TxPhys);
    memset(r->RxBuffer, 0, PAGE_SIZE * RTL8139_RX_PAGES);
    memset(r->TxBuffers, 0, PAGE_SIZE * RTL8139_TX_PAGES);

    DbgPrint("RTL8139: rx=0x%llx tx=0x%llx\n",
             (unsigned long long)r->RxPhys,
             (unsigned long long)r->TxPhys);
    return STATUS_SUCCESS;
}

static uint16_t Rtl8139RxRead16(RTL8139_DEVICE* r, uint32_t offset) {
    offset %= RTL8139_RX_RING_SIZE;
    uint16_t lo = r->RxBuffer[offset];
    uint16_t hi = r->RxBuffer[(offset + 1u) % RTL8139_RX_RING_SIZE];
    return (uint16_t)(lo | (hi << 8));
}

static void Rtl8139RxCopy(RTL8139_DEVICE* r, uint32_t offset, void* dst, uint32_t length) {
    uint8_t* out = (uint8_t*)dst;
    offset %= RTL8139_RX_RING_SIZE;

    uint32_t first = RTL8139_RX_RING_SIZE - offset;
    if (first > length)
        first = length;
    memcpy(out, r->RxBuffer + offset, first);
    if (first < length)
        memcpy(out + first, r->RxBuffer, length - first);
}

static void Rtl8139ProgramHardware(RTL8139_DEVICE* r) {
    // Wake the device and clear stale interrupts before installing buffers.
    Rtl8139Write8(r, RTL8139_REG_CONFIG1, 0x00);
    Rtl8139Write16(r, RTL8139_REG_IMR, 0);
    Rtl8139Write16(r, RTL8139_REG_ISR, 0xFFFFu);

    Rtl8139Write32(r, RTL8139_REG_RBSTART, (uint32_t)r->RxPhys);
    r->RxOffset = 0;
    Rtl8139Write16(r, RTL8139_REG_CAPR, 0xFFF0u); // CAPR is rxOffset - 16.

    for (uint32_t i = 0; i < RTL8139_TX_SLOTS; i++) {
        PHYSICAL_ADDRESS p = r->TxPhys + (PHYSICAL_ADDRESS)i * RTL8139_TX_BUF_SIZE;
        Rtl8139Write32(r, RTL8139_REG_TSAD(i), (uint32_t)p);
    }

    Rtl8139Write32(r, RTL8139_REG_TCR,
                   RTL8139_TCR_IFG_NORMAL | RTL8139_TCR_MXDMA_UNLIMITED);
    Rtl8139Write32(r, RTL8139_REG_RCR,
                   RTL8139_RCR_APM | RTL8139_RCR_AB | RTL8139_RCR_AM |
                   RTL8139_RCR_WRAP | RTL8139_RCR_RBLEN_8K |
                   RTL8139_RCR_MXDMA_UNLIMITED);

    Rtl8139MemoryBarrier();
    Rtl8139Write8(r, RTL8139_REG_CMD, RTL8139_CMD_RE | RTL8139_CMD_TE);
    Rtl8139Write16(r, RTL8139_REG_ISR, 0xFFFFu);
    Rtl8139Write16(r, RTL8139_REG_IMR, RTL8139_INTR_ENABLES);
}

static void Rtl8139HandleRx(RTL8139_DEVICE* r) {
    for (uint32_t budget = 0; budget < 64; budget++) {
        uint8_t cmd = Rtl8139Read8(r, RTL8139_REG_CMD);
        if (cmd & RTL8139_CMD_BUFE)
            break;

        uint32_t off = r->RxOffset % RTL8139_RX_RING_SIZE;
        uint16_t status = Rtl8139RxRead16(r, off);
        uint16_t packetLength = Rtl8139RxRead16(r, off + 2u);

        if (packetLength < 4 || packetLength > RTL8139_RX_WIRE_MAX) {
            DbgPrint("RTL8139: bad rx length %u status=0x%04x, resetting rx pointer\n",
                     packetLength, status);
            r->RxOffset = Rtl8139Read16(r, RTL8139_REG_CBR) % RTL8139_RX_RING_SIZE;
            Rtl8139Write16(r, RTL8139_REG_CAPR, (uint16_t)(r->RxOffset - 16u));
            break;
        }

        uint32_t frameLength = packetLength;
        if (frameLength > 4)
            frameLength -= 4; // Strip Ethernet FCS before upper-layer handoff.

        bool goodFrame = (status & RTL8139_RX_OK) &&
                         !(status & RTL8139_RX_BAD_BITS) &&
                         frameLength >= NET_ETHERNET_HEADER_LENGTH &&
                         frameLength <= NET_ETHERNET_MAX_FRAME;
        if (goodFrame) {
            if ((off + 4u + frameLength) <= RTL8139_RX_RING_SIZE) {
                NetReceiveFrame(&r->NetDevice, r->RxBuffer + off + 4u, frameLength);
            } else {
                Rtl8139RxCopy(r, off + 4u, r->RxScratch, frameLength);
                NetReceiveFrame(&r->NetDevice, r->RxScratch, frameLength);
            }
        } else {
            DbgPrint("RTL8139: rx error status=0x%04x len=%u\n", status, packetLength);
        }

        r->RxOffset = (r->RxOffset + 4u + packetLength + 3u) & ~3u;
        r->RxOffset %= RTL8139_RX_RING_SIZE;
        Rtl8139MemoryBarrier();
        Rtl8139Write16(r, RTL8139_REG_CAPR, (uint16_t)(r->RxOffset - 16u));
    }
}

static void Rtl8139DpcRoutine(KDPC* dpc, void* context, void* systemArgument1, void* systemArgument2) {
    (void)dpc;
    (void)systemArgument1;
    (void)systemArgument2;

    RTL8139_DEVICE* r = (RTL8139_DEVICE*)context;
    uint16_t status = (uint16_t)r->PendingIsr;
    r->PendingIsr = 0;

    if (status & (RTL8139_ISR_ROK | RTL8139_ISR_RER | RTL8139_ISR_RXOVW | RTL8139_ISR_FOVW))
        Rtl8139HandleRx(r);

    if (status & (RTL8139_ISR_PUN | RTL8139_ISR_LENCHG))
        DbgPrint("RTL8139: link/status change isr=0x%04x\n", status);

    if (status & (RTL8139_ISR_RER | RTL8139_ISR_TER | RTL8139_ISR_RXOVW |
                  RTL8139_ISR_FOVW | RTL8139_ISR_SYSERR))
        DbgPrint("RTL8139: interrupt error bits=0x%04x\n", status);
}

static void Rtl8139Isr(void) {
    if (!gDevicePresent)
        return;

    RTL8139_DEVICE* r = &gDevice;
    uint16_t status = Rtl8139Read16(r, RTL8139_REG_ISR);
    status &= RTL8139_INTR_ENABLES;
    if (!status || status == 0xFFFFu)
        return;

    Rtl8139Write16(r, RTL8139_REG_ISR, status);
    r->PendingIsr |= status;
    KeInsertQueueDpc(&r->Dpc, (void*)0, (void*)0);
}

static KSTATUS Rtl8139SendFrame(NET_DEVICE* device, const void* frame, size_t length) {
    if (!device || !frame)
        return STATUS_INVALID_PARAMETER;
    if (length > NET_ETHERNET_MAX_FRAME)
        return STATUS_BUFFER_TOO_SMALL;
    if (length < NET_ETHERNET_HEADER_LENGTH)
        return STATUS_INVALID_PARAMETER;

    RTL8139_DEVICE* r = (RTL8139_DEVICE*)device->DriverContext;
    if (!r)
        return STATUS_INVALID_PARAMETER;

    uintptr_t flags = KeAcquireSpinlock(&r->TxLock);
    uint32_t slot = r->TxSlot;
    uint32_t tsd = Rtl8139Read32(r, RTL8139_REG_TSD(slot));
    // RTL8139 TSD.OWN is 1 when the descriptor is idle/free.
    // Writing a command with OWN cleared hands the slot to the NIC.
    if (!(tsd & RTL8139_TSD_OWN)) {
        KeReleaseSpinlock(&r->TxLock, flags);
        return STATUS_QUEUE_FULL;
    }

    size_t wireLength = length < NET_ETHERNET_MIN_FRAME ? NET_ETHERNET_MIN_FRAME : length;
    uint8_t* buf = r->TxBuffers + slot * RTL8139_TX_BUF_SIZE;
    memcpy(buf, frame, length);
    if (wireLength > length)
        memset(buf + length, 0, wireLength - length);

    Rtl8139MemoryBarrier();
    Rtl8139Write32(r, RTL8139_REG_TSD(slot), (uint32_t)wireLength & RTL8139_TSD_SIZE_MASK);

    r->TxSlot = (slot + 1u) % RTL8139_TX_SLOTS;
    KeReleaseSpinlock(&r->TxLock, flags);
    return STATUS_SUCCESS;
}

static KSTATUS Rtl8139Initialize(const HAL_API* hal) {
    gHal = hal;
    memset(&gDevice, 0, sizeof(gDevice));
    gDevice.TxLock = (SPINLOCK)SPINLOCK_INIT;

    if (!gHal->Pci.FindDevice(RTL8139_VENDOR_REALTEK, RTL8139_DEVICE_ID,
                              &gDevice.Bus, &gDevice.Dev, &gDevice.Fn)) {
        DbgPrint("RTL8139: no PCI device 10ec:8139 found; skipping\n");
        return STATUS_SUCCESS;
    }

    DbgPrint("RTL8139: found Realtek PCI device 10ec:8139 at %u:%u.%u\n",
             gDevice.Bus, gDevice.Dev, gDevice.Fn);

    KSTATUS st = Rtl8139SelectRegisterBar(&gDevice);
    if (!KSUCCESS(st)) {
        DbgPrint("RTL8139: no usable register BAR (0x%x)\n", st);
        return st;
    }

    Rtl8139EnablePci(&gDevice);

    gDevice.Irq = hal->Pci.GetIrqLine(gDevice.Bus, gDevice.Dev, gDevice.Fn);
    if (gDevice.Irq == 0xFFu) {
        DbgPrint("RTL8139: no legacy PCI IRQ line wired\n");
        return STATUS_NOT_SUPPORTED;
    }

    // Wake, reset, then read the station address.
    Rtl8139Write8(&gDevice, RTL8139_REG_CONFIG1, 0x00);
    st = Rtl8139Reset(&gDevice);
    if (!KSUCCESS(st)) {
        DbgPrint("RTL8139: reset timed out\n");
        return st;
    }

    Rtl8139ReadMac(&gDevice);
    DbgPrint("RTL8139: MAC %02x:%02x:%02x:%02x:%02x:%02x irq=%u\n",
             gDevice.NetDevice.HardwareAddress[0], gDevice.NetDevice.HardwareAddress[1],
             gDevice.NetDevice.HardwareAddress[2], gDevice.NetDevice.HardwareAddress[3],
             gDevice.NetDevice.HardwareAddress[4], gDevice.NetDevice.HardwareAddress[5],
             gDevice.Irq);

    st = Rtl8139AllocateDma(&gDevice);
    if (!KSUCCESS(st))
        return st;

    KeInitializeDpc(&gDevice.Dpc, Rtl8139DpcRoutine, &gDevice);

    gDevice.NetDevice.Mtu = NET_MTU_ETHERNET;
    gDevice.NetDevice.DriverContext = &gDevice;
    gDevice.NetDevice.SendFrame = Rtl8139SendFrame;

    Rtl8139ProgramHardware(&gDevice);

    gDevicePresent = true;
    KeIrqRegister(gDevice.Irq, Rtl8139Isr);

    st = NetRegisterDevice(&gDevice.NetDevice);
    if (!KSUCCESS(st))
        return st;

    DbgPrint("RTL8139: initialized; RX/TX enabled on IRQ %u\n", gDevice.Irq);
    return STATUS_SUCCESS;
}

KSTATUS DriverEntry(const HAL_API* hal) {
    DbgPrint("RTL8139: driver loading...\n");
    KSTATUS st = Rtl8139Initialize(hal);
    if (!KSUCCESS(st))
        DbgPrint("RTL8139: init failed: 0x%x\n", st);
    return st;
}