path: root/hw/pci/pcie.c

/*
 * pcie.c
 *
 * Copyright (c) 2010 Isaku Yamahata <yamahata at valinux co jp>
 *                    VA Linux Systems Japan K.K.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include "qemu-common.h"
#include "hw/pci/pci_bridge.h"
#include "hw/pci/pcie.h"
#include "hw/pci/msix.h"
#include "hw/pci/msi.h"
#include "hw/pci/pci_bus.h"
#include "hw/pci/pcie_regs.h"
#include "qemu/range.h"

//#define DEBUG_PCIE
#ifdef DEBUG_PCIE
# define PCIE_DPRINTF(fmt, ...)                                         \
    fprintf(stderr, "%s:%d " fmt, __func__, __LINE__, ## __VA_ARGS__)
#else
# define PCIE_DPRINTF(fmt, ...) do {} while (0)
#endif
#define PCIE_DEV_PRINTF(dev, fmt, ...)                                  \
    PCIE_DPRINTF("%s:%x "fmt, (dev)->name, (dev)->devfn, ## __VA_ARGS__)


/***************************************************************************
 * pci express capability helper functions
 */
int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
{
    int pos;
    uint8_t *exp_cap;

    assert(pci_is_express(dev));

    pos = pci_add_capability(dev, PCI_CAP_ID_EXP, offset,
                                 PCI_EXP_VER2_SIZEOF);
    if (pos < 0) {
        return pos;
    }
    dev->exp.exp_cap = pos;
    exp_cap = dev->config + pos;

    /* capability register
       interrupt message number defaults to 0 */
    pci_set_word(exp_cap + PCI_EXP_FLAGS,
                 ((type << PCI_EXP_FLAGS_TYPE_SHIFT) & PCI_EXP_FLAGS_TYPE) |
                 PCI_EXP_FLAGS_VER2);

    /* device capability register
     * table 7-12:
     * roll based error reporting bit must be set by all
     * Functions conforming to the ECN, PCI Express Base
     * Specification, Revision 1.1., or subsequent PCI Express Base
     * Specification revisions.
     */
    pci_set_long(exp_cap + PCI_EXP_DEVCAP, PCI_EXP_DEVCAP_RBER);

    pci_set_long(exp_cap + PCI_EXP_LNKCAP,
                 (port << PCI_EXP_LNKCAP_PN_SHIFT) |
                 PCI_EXP_LNKCAP_ASPMS_0S |
                 PCI_EXP_LNK_MLW_1 |
                 PCI_EXP_LNK_LS_25);

    pci_set_word(exp_cap + PCI_EXP_LNKSTA,
                 PCI_EXP_LNK_MLW_1 | PCI_EXP_LNK_LS_25 |PCI_EXP_LNKSTA_DLLLA);

    pci_set_long(exp_cap + PCI_EXP_DEVCAP2,
                 PCI_EXP_DEVCAP2_EFF | PCI_EXP_DEVCAP2_EETLPP);

    pci_set_word(dev->wmask + pos + PCI_EXP_DEVCTL2, PCI_EXP_DEVCTL2_EETLPPB);
    return pos;
}

int pcie_endpoint_cap_init(PCIDevice *dev, uint8_t offset)
{
    uint8_t type = PCI_EXP_TYPE_ENDPOINT;

    /*
     * Windows guests will report Code 10, device cannot start, if
     * a regular Endpoint type is exposed on a root complex.  These
     * should instead be Root Complex Integrated Endpoints.
     */
    if (pci_bus_is_express(dev->bus) && pci_bus_is_root(dev->bus)) {
        type = PCI_EXP_TYPE_RC_END;
    }

    return pcie_cap_init(dev, offset, type, 0);
}

void pcie_cap_exit(PCIDevice *dev)
{
    pci_del_capability(dev, PCI_CAP_ID_EXP, PCI_EXP_VER2_SIZEOF);
}

uint8_t pcie_cap_get_type(const PCIDevice *dev)
{
    uint32_t pos = dev->exp.exp_cap;
    assert(pos > 0);
    return (pci_get_word(dev->config + pos + PCI_EXP_FLAGS) &
            PCI_EXP_FLAGS_TYPE) >> PCI_EXP_FLAGS_TYPE_SHIFT;
}

/* MSI/MSI-X */
/* pci express interrupt message number */
/* 7.8.2 PCI Express Capabilities Register: Interrupt Message Number */
void pcie_cap_flags_set_vector(PCIDevice *dev, uint8_t vector)
{
    uint8_t *exp_cap = dev->config + dev->exp.exp_cap;
    assert(vector < 32);
    pci_word_test_and_clear_mask(exp_cap + PCI_EXP_FLAGS, PCI_EXP_FLAGS_IRQ);
    pci_word_test_and_set_mask(exp_cap + PCI_EXP_FLAGS,
                               vector << PCI_EXP_FLAGS_IRQ_SHIFT);
}

uint8_t pcie_cap_flags_get_vector(PCIDevice *dev)
{
    return (pci_get_word(dev->config + dev->exp.exp_cap + PCI_EXP_FLAGS) &
            PCI_EXP_FLAGS_IRQ) >> PCI_EXP_FLAGS_IRQ_SHIFT;
}

void pcie_cap_deverr_init(PCIDevice *dev)
{
    uint32_t pos = dev->exp.exp_cap;
    pci_long_test_and_set_mask(dev->config + pos + PCI_EXP_DEVCAP,
                               PCI_EXP_DEVCAP_RBER);
    pci_long_test_and_set_mask(dev->wmask + pos + PCI_EXP_DEVCTL,
                               PCI_EXP_DEVCTL_CERE | PCI_EXP_DEVCTL_NFERE |
                               PCI_EXP_DEVCTL_FERE | PCI_EXP_DEVCTL_URRE);
    pci_long_test_and_set_mask(dev->w1cmask + pos + PCI_EXP_DEVSTA,
                               PCI_EXP_DEVSTA_CED | PCI_EXP_DEVSTA_NFED |
                               PCI_EXP_DEVSTA_FED | PCI_EXP_DEVSTA_URD);
}

void pcie_cap_deverr_reset(PCIDevice *dev)
{
    uint8_t *devctl = dev->config + dev->exp.exp_cap + PCI_EXP_DEVCTL;
    pci_long_test_and_clear_mask(devctl,
                                 PCI_EXP_DEVCTL_CERE | PCI_EXP_DEVCTL_NFERE |
                                 PCI_EXP_DEVCTL_FERE | PCI_EXP_DEVCTL_URRE);
}

static void hotplug_event_update_event_status(PCIDevice *dev)
{
    uint32_t pos = dev->exp.exp_cap;
    uint8_t *exp_cap = dev->config + pos;
    uint16_t sltctl = pci_get_word(exp_cap + PCI_EXP_SLTCTL);
    uint16_t sltsta = pci_get_word(exp_cap + PCI_EXP_SLTSTA);

    dev->exp.hpev_notified = (sltctl & PCI_EXP_SLTCTL_HPIE) &&
        (sltsta & sltctl & PCI_EXP_HP_EV_SUPPORTED);
}

static void hotplug_event_notify(PCIDevice *dev)
{
    bool prev = dev->exp.hpev_notified;

    hotplug_event_update_event_status(dev);

    if (prev == dev->exp.hpev_notified) {
        return;
    }

    /* Note: the logic above does not take into account whether interrupts
     * are masked. The result is that interrupt will be sent when it is
     * subsequently unmasked. This appears to be legal: Section 6.7.3.4:
     * The Port may optionally send an MSI when there are hot-plug events that
     * occur while interrupt generation is disabled, and interrupt generation is
     * subsequently enabled. */
    if (msix_enabled(dev)) {
        msix_notify(dev, pcie_cap_flags_get_vector(dev));
    } else if (msi_enabled(dev)) {
        msi_notify(dev, pcie_cap_flags_get_vector(dev));
    } else {
        pci_set_irq(dev, dev->exp.hpev_notified);
    }
}

static void hotplug_event_clear(PCIDevice *dev)
{
    hotplug_event_update_event_status(dev);
    if (!msix_enabled(dev) && !msi_enabled(dev) && !dev->exp.hpev_notified) {
        pci_irq_deassert(dev);
    }
}

/*
 * A PCI Express Hot-Plug Event has occurred, so update slot status register
 * and notify OS of the event if necessary.
 *
 * 6.7.3 PCI Express Hot-Plug Events
 * 6.7.3.4 Software Notification of Hot-Plug Events
 */
static void pcie_cap_slot_event(PCIDevice *dev, PCIExpressHotPlugEvent event)
{
    /* Minor optimization: if nothing changed - no event is needed. */
    if (pci_word_test_and_set_mask(dev->config + dev->exp.exp_cap +
                                   PCI_EXP_SLTSTA, event)) {
        return;
    }
    hotplug_event_notify(dev);
}

static void pcie_cap_slot_hotplug_common(PCIDevice *hotplug_dev,
                                         DeviceState *dev,
                                         uint8_t **exp_cap, Error **errp)
{
    *exp_cap = hotplug_dev->config + hotplug_dev->exp.exp_cap;
    uint16_t sltsta = pci_get_word(*exp_cap + PCI_EXP_SLTSTA);

    PCIE_DEV_PRINTF(PCI_DEVICE(dev), "hotplug state: 0x%x\n", sltsta);
    if (sltsta & PCI_EXP_SLTSTA_EIS) {
        /* the slot is electromechanically locked.
         * This error is propagated up to qdev and then to HMP/QMP.
         */
        error_setg_errno(errp, EBUSY, "slot is electromechanically locked");
    }
}

void pcie_cap_slot_hotplug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
                              Error **errp)
{
    uint8_t *exp_cap;
    PCIDevice *pci_dev = PCI_DEVICE(dev);

    pcie_cap_slot_hotplug_common(PCI_DEVICE(hotplug_dev), dev, &exp_cap, errp);

    /* Don't send event when device is enabled during qemu machine creation:
     * it is present on boot, no hotplug event is necessary. We do send an
     * event when the device is disabled later. */
    if (!dev->hotplugged) {
        pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
                                   PCI_EXP_SLTSTA_PDS);
        return;
    }

    /* To enable multifunction hot-plug, we just ensure the function
     * 0 added last. When function 0 is added, we set the sltsta and
     * inform OS via event notification.
     */
    if (pci_get_function_0(pci_dev)) {
        pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
                                   PCI_EXP_SLTSTA_PDS);
        pcie_cap_slot_event(PCI_DEVICE(hotplug_dev),
                            PCI_EXP_HP_EV_PDC | PCI_EXP_HP_EV_ABP);
    }
}

static void pcie_unplug_device(PCIBus *bus, PCIDevice *dev, void *opaque)
{
    object_unparent(OBJECT(dev));
}

void pcie_cap_slot_hot_unplug_request_cb(HotplugHandler *hotplug_dev,
                                         DeviceState *dev, Error **errp)
{
    uint8_t *exp_cap;
    PCIDevice *pci_dev = PCI_DEVICE(dev);
    PCIBus *bus = pci_dev->bus;

    pcie_cap_slot_hotplug_common(PCI_DEVICE(hotplug_dev), dev, &exp_cap, errp);

    /* In case user cancel the operation of multi-function hot-add,
     * remove the function that is unexposed to guest individually,
     * without interaction with guest.
     */
    if (pci_dev->devfn &&
        !bus->devices[0]) {
        pcie_unplug_device(bus, pci_dev, NULL);

        return;
    }

    pcie_cap_slot_push_attention_button(PCI_DEVICE(hotplug_dev));
}

/* pci express slot for pci express root/downstream port
   PCI express capability slot registers */
void pcie_cap_slot_init(PCIDevice *dev, uint16_t slot)
{
    uint32_t pos = dev->exp.exp_cap;

    pci_word_test_and_set_mask(dev->config + pos + PCI_EXP_FLAGS,
                               PCI_EXP_FLAGS_SLOT);

    pci_long_test_and_clear_mask(dev->config + pos + PCI_EXP_SLTCAP,
                                 ~PCI_EXP_SLTCAP_PSN);
    pci_long_test_and_set_mask(dev->config + pos + PCI_EXP_SLTCAP,
                               (slot << PCI_EXP_SLTCAP_PSN_SHIFT) |
                               PCI_EXP_SLTCAP_EIP |
                               PCI_EXP_SLTCAP_HPS |
                               PCI_EXP_SLTCAP_HPC |
                               PCI_EXP_SLTCAP_PIP |
                               PCI_EXP_SLTCAP_AIP |
                               PCI_EXP_SLTCAP_ABP);

    if (dev->cap_present & QEMU_PCIE_SLTCAP_PCP) {
        pci_long_test_and_set_mask(dev->config + pos + PCI_EXP_SLTCAP,
                                   PCI_EXP_SLTCAP_PCP);
        pci_word_test_and_clear_mask(dev->config + pos + PCI_EXP_SLTCTL,
                                     PCI_EXP_SLTCTL_PCC);
        pci_word_test_and_set_mask(dev->wmask + pos + PCI_EXP_SLTCTL,
                                   PCI_EXP_SLTCTL_PCC);
    }

    pci_word_test_and_clear_mask(dev->config + pos + PCI_EXP_SLTCTL,
                                 PCI_EXP_SLTCTL_PIC |
                                 PCI_EXP_SLTCTL_AIC);
    pci_word_test_and_set_mask(dev->config + pos + PCI_EXP_SLTCTL,
                               PCI_EXP_SLTCTL_PIC_OFF |
                               PCI_EXP_SLTCTL_AIC_OFF);
    pci_word_test_and_set_mask(dev->wmask + pos + PCI_EXP_SLTCTL,
                               PCI_EXP_SLTCTL_PIC |
                               PCI_EXP_SLTCTL_AIC |
                               PCI_EXP_SLTCTL_HPIE |
                               PCI_EXP_SLTCTL_CCIE |
                               PCI_EXP_SLTCTL_PDCE |
                               PCI_EXP_SLTCTL_ABPE);
    /* Although reading PCI_EXP_SLTCTL_EIC returns always 0,
     * make the bit writable here in order to detect 1b is written.
     * pcie_cap_slot_write_config() test-and-clear the bit, so
     * this bit always returns 0 to the guest.
     */
    pci_word_test_and_set_mask(dev->wmask + pos + PCI_EXP_SLTCTL,
                               PCI_EXP_SLTCTL_EIC);

    pci_word_test_and_set_mask(dev->w1cmask + pos + PCI_EXP_SLTSTA,
                               PCI_EXP_HP_EV_SUPPORTED);

    dev->exp.hpev_notified = false;

    qbus_set_hotplug_handler(BUS(pci_bridge_get_sec_bus(PCI_BRIDGE(dev))),
                             DEVICE(dev), NULL);
}

void pcie_cap_slot_reset(PCIDevice *dev)
{
    uint8_t *exp_cap = dev->config + dev->exp.exp_cap;
    uint8_t port_type = pcie_cap_get_type(dev);

    assert(port_type == PCI_EXP_TYPE_DOWNSTREAM ||
           port_type == PCI_EXP_TYPE_ROOT_PORT);

    PCIE_DEV_PRINTF(dev, "reset\n");

    pci_word_test_and_clear_mask(exp_cap + PCI_EXP_SLTCTL,
                                 PCI_EXP_SLTCTL_EIC |
                                 PCI_EXP_SLTCTL_PIC |
                                 PCI_EXP_SLTCTL_AIC |
                                 PCI_EXP_SLTCTL_HPIE |
                                 PCI_EXP_SLTCTL_CCIE |
                                 PCI_EXP_SLTCTL_PDCE |
                                 PCI_EXP_SLTCTL_ABPE);
    pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTCTL,
                               PCI_EXP_SLTCTL_AIC_OFF);

    if (dev->cap_present & QEMU_PCIE_SLTCAP_PCP) {
        /* Downstream ports enforce device number 0. */
        bool populated = pci_bridge_get_sec_bus(PCI_BRIDGE(dev))->devices[0];
        uint16_t pic;

        if (populated) {
            pci_word_test_and_clear_mask(exp_cap + PCI_EXP_SLTCTL,
                                         PCI_EXP_SLTCTL_PCC);
        } else {
            pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTCTL,
                                       PCI_EXP_SLTCTL_PCC);
        }

        pic = populated ? PCI_EXP_SLTCTL_PIC_ON : PCI_EXP_SLTCTL_PIC_OFF;
        pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTCTL, pic);
    }

    pci_word_test_and_clear_mask(exp_cap + PCI_EXP_SLTSTA,
                                 PCI_EXP_SLTSTA_EIS |/* on reset,
                                                        the lock is released */
                                 PCI_EXP_SLTSTA_CC |
                                 PCI_EXP_SLTSTA_PDC |
                                 PCI_EXP_SLTSTA_ABP);

    hotplug_event_update_event_status(dev);
}

void pcie_cap_slot_write_config(PCIDevice *dev,
                                uint32_t addr, uint32_t val, int len)
{
    uint32_t pos = dev->exp.exp_cap;
    uint8_t *exp_cap = dev->config + pos;
    uint16_t sltsta = pci_get_word(exp_cap + PCI_EXP_SLTSTA);

    if (ranges_overlap(addr, len, pos + PCI_EXP_SLTSTA, 2)) {
        hotplug_event_clear(dev);
    }

    if (!ranges_overlap(addr, len, pos + PCI_EXP_SLTCTL, 2)) {
        return;
    }

    if (pci_word_test_and_clear_mask(exp_cap + PCI_EXP_SLTCTL,
                                     PCI_EXP_SLTCTL_EIC)) {
        sltsta ^= PCI_EXP_SLTSTA_EIS; /* toggle PCI_EXP_SLTSTA_EIS bit */
        pci_set_word(exp_cap + PCI_EXP_SLTSTA, sltsta);
        PCIE_DEV_PRINTF(dev, "PCI_EXP_SLTCTL_EIC: "
                        "sltsta -> 0x%02"PRIx16"\n",
                        sltsta);
    }

    /*
     * If the slot is polulated, power indicator is off and power
     * controller is off, it is safe to detach the devices.
     */
    if ((sltsta & PCI_EXP_SLTSTA_PDS) && (val & PCI_EXP_SLTCTL_PCC) &&
        ((val & PCI_EXP_SLTCTL_PIC_OFF) == PCI_EXP_SLTCTL_PIC_OFF)) {
            PCIBus *sec_bus = pci_bridge_get_sec_bus(PCI_BRIDGE(dev));
            pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
                                pcie_unplug_device, NULL);

            pci_word_test_and_clear_mask(exp_cap + PCI_EXP_SLTSTA,
                                         PCI_EXP_SLTSTA_PDS);
            pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
                                       PCI_EXP_SLTSTA_PDC);
    }

    hotplug_event_notify(dev);

    /* 
     * 6.7.3.2 Command Completed Events
     *
     * Software issues a command to a hot-plug capable Downstream Port by
     * issuing a write transaction that targets any portion of the Port’s Slot
     * Control register. A single write to the Slot Control register is
     * considered to be a single command, even if the write affects more than
     * one field in the Slot Control register. In response to this transaction,
     * the Port must carry out the requested actions and then set the
     * associated status field for the command completed event. */

    /* Real hardware might take a while to complete requested command because
     * physical movement would be involved like locking the electromechanical
     * lock.  However in our case, command is completed instantaneously above,
     * so send a command completion event right now.
     */
    pcie_cap_slot_event(dev, PCI_EXP_HP_EV_CCI);
}

int pcie_cap_slot_post_load(void *opaque, int version_id)
{
    PCIDevice *dev = opaque;
    hotplug_event_update_event_status(dev);
    return 0;
}

void pcie_cap_slot_push_attention_button(PCIDevice *dev)
{
    pcie_cap_slot_event(dev, PCI_EXP_HP_EV_ABP);
}

/* root control/capabilities/status. PME isn't emulated for now */
void pcie_cap_root_init(PCIDevice *dev)
{
    pci_set_word(dev->wmask + dev->exp.exp_cap + PCI_EXP_RTCTL,
                 PCI_EXP_RTCTL_SECEE | PCI_EXP_RTCTL_SENFEE |
                 PCI_EXP_RTCTL_SEFEE);
}

void pcie_cap_root_reset(PCIDevice *dev)
{
    pci_set_word(dev->config + dev->exp.exp_cap + PCI_EXP_RTCTL, 0);
}

/* function level reset(FLR) */
void pcie_cap_flr_init(PCIDevice *dev)
{
    pci_long_test_and_set_mask(dev->config + dev->exp.exp_cap + PCI_EXP_DEVCAP,
                               PCI_EXP_DEVCAP_FLR);

    /* Although reading BCR_FLR returns always 0,
     * the bit is made writable here in order to detect the 1b is written
     * pcie_cap_flr_write_config() test-and-clear the bit, so
     * this bit always returns 0 to the guest.
     */
    pci_word_test_and_set_mask(dev->wmask + dev->exp.exp_cap + PCI_EXP_DEVCTL,
                               PCI_EXP_DEVCTL_BCR_FLR);
}

void pcie_cap_flr_write_config(PCIDevice *dev,
                               uint32_t addr, uint32_t val, int len)
{
    uint8_t *devctl = dev->config + dev->exp.exp_cap + PCI_EXP_DEVCTL;
    if (pci_get_word(devctl) & PCI_EXP_DEVCTL_BCR_FLR) {
        /* Clear PCI_EXP_DEVCTL_BCR_FLR after invoking the reset handler
           so the handler can detect FLR by looking at this bit. */
        pci_device_reset(dev);
        pci_word_test_and_clear_mask(devctl, PCI_EXP_DEVCTL_BCR_FLR);
    }
}

/* Alternative Routing-ID Interpretation (ARI)
 * forwarding support for root and downstream ports
 */
void pcie_cap_arifwd_init(PCIDevice *dev)
{
    uint32_t pos = dev->exp.exp_cap;
    pci_long_test_and_set_mask(dev->config + pos + PCI_EXP_DEVCAP2,
                               PCI_EXP_DEVCAP2_ARI);
    pci_long_test_and_set_mask(dev->wmask + pos + PCI_EXP_DEVCTL2,
                               PCI_EXP_DEVCTL2_ARI);
}

void pcie_cap_arifwd_reset(PCIDevice *dev)
{
    uint8_t *devctl2 = dev->config + dev->exp.exp_cap + PCI_EXP_DEVCTL2;
    pci_long_test_and_clear_mask(devctl2, PCI_EXP_DEVCTL2_ARI);
}

bool pcie_cap_is_arifwd_enabled(const PCIDevice *dev)
{
    if (!pci_is_express(dev)) {
        return false;
    }
    if (!dev->exp.exp_cap) {
        return false;
    }

    return pci_get_long(dev->config + dev->exp.exp_cap + PCI_EXP_DEVCTL2) &
        PCI_EXP_DEVCTL2_ARI;
}

/**************************************************************************
 * pci express extended capability list management functions
 * uint16_t ext_cap_id (16 bit)
 * uint8_t cap_ver (4 bit)
 * uint16_t cap_offset (12 bit)
 * uint16_t ext_cap_size
 */

static uint16_t pcie_find_capability_list(PCIDevice *dev, uint16_t cap_id,
                                          uint16_t *prev_p)
{
    uint16_t prev = 0;
    uint16_t next;
    uint32_t header = pci_get_long(dev->config + PCI_CONFIG_SPACE_SIZE);

    if (!header) {
        /* no extended capability */
        next = 0;
        goto out;
    }
    for (next = PCI_CONFIG_SPACE_SIZE; next;
         prev = next, next = PCI_EXT_CAP_NEXT(header)) {

        assert(next >= PCI_CONFIG_SPACE_SIZE);
        assert(next <= PCIE_CONFIG_SPACE_SIZE - 8);

        header = pci_get_long(dev->config + next);
        if (PCI_EXT_CAP_ID(header) == cap_id) {
            break;
        }
    }

out:
    if (prev_p) {
        *prev_p = prev;
    }
    return next;
}

uint16_t pcie_find_capability(PCIDevice *dev, uint16_t cap_id)
{
    return pcie_find_capability_list(dev, cap_id, NULL);
}

static void pcie_ext_cap_set_next(PCIDevice *dev, uint16_t pos, uint16_t next)
{
    uint32_t header = pci_get_long(dev->config + pos);
    assert(!(next & (PCI_EXT_CAP_ALIGN - 1)));
    header = (header & ~PCI_EXT_CAP_NEXT_MASK) |
        ((next << PCI_EXT_CAP_NEXT_SHIFT) & PCI_EXT_CAP_NEXT_MASK);
    pci_set_long(dev->config + pos, header);
}

/*
 * caller must supply valid (offset, size) * such that the range shouldn't
 * overlap with other capability or other registers.
 * This function doesn't check it.
 */
void pcie_add_capability(PCIDevice *dev,
                         uint16_t cap_id, uint8_t cap_ver,
                         uint16_t offset, uint16_t size)
{
    uint32_t header;
    uint16_t next;

    assert(offset >= PCI_CONFIG_SPACE_SIZE);
    assert(offset < offset + size);
    assert(offset + size < PCIE_CONFIG_SPACE_SIZE);
    assert(size >= 8);
    assert(pci_is_express(dev));

    if (offset == PCI_CONFIG_SPACE_SIZE) {
        header = pci_get_long(dev->config + offset);
        next = PCI_EXT_CAP_NEXT(header);
    } else {
        uint16_t prev;

        /* 0 is reserved cap id. use internally to find the last capability
           in the linked list */
        next = pcie_find_capability_list(dev, 0, &prev);

        assert(prev >= PCI_CONFIG_SPACE_SIZE);
        assert(next == 0);
        pcie_ext_cap_set_next(dev, prev, offset);
    }
    pci_set_long(dev->config + offset, PCI_EXT_CAP(cap_id, cap_ver, next));

    /* Make capability read-only by default */
    memset(dev->wmask + offset, 0, size);
    memset(dev->w1cmask + offset, 0, size);
    /* Check capability by default */
    memset(dev->cmask + offset, 0xFF, size);
}

/**************************************************************************
 * pci express extended capability helper functions
 */

/* ARI */
void pcie_ari_init(PCIDevice *dev, uint16_t offset, uint16_t nextfn)
{
    pcie_add_capability(dev, PCI_EXT_CAP_ID_ARI, PCI_ARI_VER,
                        offset, PCI_ARI_SIZEOF);
    pci_set_long(dev->config + offset + PCI_ARI_CAP, (nextfn & 0xff) << 8);
}