// SPDX-License-Identifier: GPL-2.0
/*
 * Xen PCI Frontend
 *
 * Author: Ryan Wilson <hap9@epoch.ncsc.mil>
 */
#include <linux/module.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <xen/xenbus.h>
#include <xen/events.h>
#include <xen/grant_table.h>
#include <xen/page.h>
#include <linux/spinlock.h>
#include <linux/pci.h>
#include <linux/msi.h>
#include <xen/interface/io/pciif.h>
#include <asm/xen/pci.h>
#include <linux/interrupt.h>
#include <linux/atomic.h>
#include <linux/workqueue.h>
#include <linux/bitops.h>
#include <linux/time.h>
#include <linux/ktime.h>
#include <xen/platform_pci.h>

#include <asm/xen/swiotlb-xen.h>

#define INVALID_EVTCHN    (-1)

struct pci_bus_entry {
        struct list_head list;
        struct pci_bus *bus;
};

#define _PDEVB_op_active                (0)
#define PDEVB_op_active                 (1 << (_PDEVB_op_active))

struct pcifront_device {
        struct xenbus_device *xdev;
        struct list_head root_buses;

        int evtchn;
        grant_ref_t gnt_ref;

        int irq;

        /* Lock this when doing any operations in sh_info */
        spinlock_t sh_info_lock;
        struct xen_pci_sharedinfo *sh_info;
        struct work_struct op_work;
        unsigned long flags;

};

struct pcifront_sd {
        struct pci_sysdata sd;
        struct pcifront_device *pdev;
};

static inline struct pcifront_device *
pcifront_get_pdev(struct pcifront_sd *sd)
{
        return sd->pdev;
}

static inline void pcifront_init_sd(struct pcifront_sd *sd,
                                    unsigned int domain, unsigned int bus,
                                    struct pcifront_device *pdev)
{
        /* Because we do not expose that information via XenBus. */
        sd->sd.node = first_online_node;
        sd->sd.domain = domain;
        sd->pdev = pdev;
}

static DEFINE_SPINLOCK(pcifront_dev_lock);
static struct pcifront_device *pcifront_dev;

static int errno_to_pcibios_err(int errno)
{
        switch (errno) {
        case XEN_PCI_ERR_success:
                return PCIBIOS_SUCCESSFUL;

        case XEN_PCI_ERR_dev_not_found:
                return PCIBIOS_DEVICE_NOT_FOUND;

        case XEN_PCI_ERR_invalid_offset:
        case XEN_PCI_ERR_op_failed:
                return PCIBIOS_BAD_REGISTER_NUMBER;

        case XEN_PCI_ERR_not_implemented:
                return PCIBIOS_FUNC_NOT_SUPPORTED;

        case XEN_PCI_ERR_access_denied:
                return PCIBIOS_SET_FAILED;
        }
        return errno;
}

static inline void schedule_pcifront_aer_op(struct pcifront_device *pdev)
{
        if (test_bit(_XEN_PCIB_active, (unsigned long *)&pdev->sh_info->flags)
                && !test_and_set_bit(_PDEVB_op_active, &pdev->flags)) {
                dev_dbg(&pdev->xdev->dev, "schedule aer frontend job\n");
                schedule_work(&pdev->op_work);
        }
}

static int do_pci_op(struct pcifront_device *pdev, struct xen_pci_op *op)
{
        int err = 0;
        struct xen_pci_op *active_op = &pdev->sh_info->op;
        unsigned long irq_flags;
        evtchn_port_t port = pdev->evtchn;
        unsigned int irq = pdev->irq;
        s64 ns, ns_timeout;

        spin_lock_irqsave(&pdev->sh_info_lock, irq_flags);

        memcpy(active_op, op, sizeof(struct xen_pci_op));

        /* Go */
        wmb();
        set_bit(_XEN_PCIF_active, (unsigned long *)&pdev->sh_info->flags);
        notify_remote_via_evtchn(port);

        /*
         * We set a poll timeout of 3 seconds but give up on return after
         * 2 seconds. It is better to time out too late rather than too early
         * (in the latter case we end up continually re-executing poll() with a
         * timeout in the past). 1s difference gives plenty of slack for error.
         */
        ns_timeout = ktime_get_ns() + 2 * (s64)NSEC_PER_SEC;

        xen_clear_irq_pending(irq);

        while (test_bit(_XEN_PCIF_active,
                        (unsigned long *)&pdev->sh_info->flags)) {
                xen_poll_irq_timeout(irq, jiffies + 3*HZ);
                xen_clear_irq_pending(irq);
                ns = ktime_get_ns();
                if (ns > ns_timeout) {
                        dev_err(&pdev->xdev->dev,
                                "pciback not responding!!!\n");
                        clear_bit(_XEN_PCIF_active,
                                  (unsigned long *)&pdev->sh_info->flags);
                        err = XEN_PCI_ERR_dev_not_found;
                        goto out;
                }
        }

        /*
         * We might lose backend service request since we
         * reuse same evtchn with pci_conf backend response. So re-schedule
         * aer pcifront service.
         */
        if (test_bit(_XEN_PCIB_active,
                        (unsigned long *)&pdev->sh_info->flags)) {
                dev_err(&pdev->xdev->dev,
                        "schedule aer pcifront service\n");
                schedule_pcifront_aer_op(pdev);
        }

        memcpy(op, active_op, sizeof(struct xen_pci_op));

        err = op->err;
out:
        spin_unlock_irqrestore(&pdev->sh_info_lock, irq_flags);
        return err;
}

/* Access to this function is spinlocked in drivers/pci/access.c */
static int pcifront_bus_read(struct pci_bus *bus, unsigned int devfn,
                             int where, int size, u32 *val)
{
        int err = 0;
        struct xen_pci_op op = {
                .cmd    = XEN_PCI_OP_conf_read,
                .domain = pci_domain_nr(bus),
                .bus    = bus->number,
                .devfn  = devfn,
                .offset = where,
                .size   = size,
        };
        struct pcifront_sd *sd = bus->sysdata;
        struct pcifront_device *pdev = pcifront_get_pdev(sd);

        dev_dbg(&pdev->xdev->dev,
                "read dev=%04x:%02x:%02x.%d - offset %x size %d\n",
                pci_domain_nr(bus), bus->number, PCI_SLOT(devfn),
                PCI_FUNC(devfn), where, size);

        err = do_pci_op(pdev, &op);

        if (likely(!err)) {
                dev_dbg(&pdev->xdev->dev, "read got back value %x\n",
                        op.value);

                *val = op.value;
        } else if (err == -ENODEV) {
                /* No device here, pretend that it just returned 0 */
                err = 0;
                *val = 0;
        }

        return errno_to_pcibios_err(err);
}

/* Access to this function is spinlocked in drivers/pci/access.c */
static int pcifront_bus_write(struct pci_bus *bus, unsigned int devfn,
                              int where, int size, u32 val)
{
        struct xen_pci_op op = {
                .cmd    = XEN_PCI_OP_conf_write,
                .domain = pci_domain_nr(bus),
                .bus    = bus->number,
                .devfn  = devfn,
                .offset = where,
                .size   = size,
                .value  = val,
        };
        struct pcifront_sd *sd = bus->sysdata;
        struct pcifront_device *pdev = pcifront_get_pdev(sd);

        dev_dbg(&pdev->xdev->dev,
                "write dev=%04x:%02x:%02x.%d - offset %x size %d val %x\n",
                pci_domain_nr(bus), bus->number,
                PCI_SLOT(devfn), PCI_FUNC(devfn), where, size, val);

        return errno_to_pcibios_err(do_pci_op(pdev, &op));
}

static struct pci_ops pcifront_bus_ops = {
        .read = pcifront_bus_read,
        .write = pcifront_bus_write,
};

#ifdef CONFIG_PCI_MSI
static int pci_frontend_enable_msix(struct pci_dev *dev,
                                    int vector[], int nvec)
{
        int err;
        int i;
        struct xen_pci_op op = {
                .cmd    = XEN_PCI_OP_enable_msix,
                .domain = pci_domain_nr(dev->bus),
                .bus = dev->bus->number,
                .devfn = dev->devfn,
                .value = nvec,
        };
        struct pcifront_sd *sd = dev->bus->sysdata;
        struct pcifront_device *pdev = pcifront_get_pdev(sd);
        struct msi_desc *entry;

        if (nvec > SH_INFO_MAX_VEC) {
                pci_err(dev, "too many vectors (0x%x) for PCI frontend:"
                                   " Increase SH_INFO_MAX_VEC\n", nvec);
                return -EINVAL;
        }

        i = 0;
        msi_for_each_desc(entry, &dev->dev, MSI_DESC_NOTASSOCIATED) {
                op.msix_entries[i].entry = entry->msi_index;
                /* Vector is useless at this point. */
                op.msix_entries[i].vector = -1;
                i++;
        }

        err = do_pci_op(pdev, &op);

        if (likely(!err)) {
                if (likely(!op.value)) {
                        /* we get the result */
                        for (i = 0; i < nvec; i++) {
                                if (op.msix_entries[i].vector <= 0) {
                                        pci_warn(dev, "MSI-X entry %d is invalid: %d!\n",
                                                i, op.msix_entries[i].vector);
                                        err = -EINVAL;
                                        vector[i] = -1;
                                        continue;
                                }
                                vector[i] = op.msix_entries[i].vector;
                        }
                } else {
                        pr_info("enable msix get value %x\n", op.value);
                        err = op.value;
                }
        } else {
                pci_err(dev, "enable msix get err %x\n", err);
        }
        return err;
}

static void pci_frontend_disable_msix(struct pci_dev *dev)
{
        int err;
        struct xen_pci_op op = {
                .cmd    = XEN_PCI_OP_disable_msix,
                .domain = pci_domain_nr(dev->bus),
                .bus = dev->bus->number,
                .devfn = dev->devfn,
        };
        struct pcifront_sd *sd = dev->bus->sysdata;
        struct pcifront_device *pdev = pcifront_get_pdev(sd);

        err = do_pci_op(pdev, &op);

        /* What should do for error ? */
        if (err)
                pci_err(dev, "pci_disable_msix get err %x\n", err);
}

static int pci_frontend_enable_msi(struct pci_dev *dev, int vector[])
{
        int err;
        struct xen_pci_op op = {
                .cmd    = XEN_PCI_OP_enable_msi,
                .domain = pci_domain_nr(dev->bus),
                .bus = dev->bus->number,
                .devfn = dev->devfn,
        };
        struct pcifront_sd *sd = dev->bus->sysdata;
        struct pcifront_device *pdev = pcifront_get_pdev(sd);

        err = do_pci_op(pdev, &op);
        if (likely(!err)) {
                vector[0] = op.value;
                if (op.value <= 0) {
                        pci_warn(dev, "MSI entry is invalid: %d!\n",
                                op.value);
                        err = -EINVAL;
                        vector[0] = -1;
                }
        } else {
                pci_err(dev, "pci frontend enable msi failed for dev "
                                    "%x:%x\n", op.bus, op.devfn);
                err = -EINVAL;
        }
        return err;
}

static void pci_frontend_disable_msi(struct pci_dev *dev)
{
        int err;
        struct xen_pci_op op = {
                .cmd    = XEN_PCI_OP_disable_msi,
                .domain = pci_domain_nr(dev->bus),
                .bus = dev->bus->number,
                .devfn = dev->devfn,
        };
        struct pcifront_sd *sd = dev->bus->sysdata;
        struct pcifront_device *pdev = pcifront_get_pdev(sd);

        err = do_pci_op(pdev, &op);
        if (err == XEN_PCI_ERR_dev_not_found) {
                /* XXX No response from backend, what shall we do? */
                pr_info("get no response from backend for disable MSI\n");
                return;
        }
        if (err)
                /* how can pciback notify us fail? */
                pr_info("get fake response from backend\n");
}

static struct xen_pci_frontend_ops pci_frontend_ops = {
        .enable_msi = pci_frontend_enable_msi,
        .disable_msi = pci_frontend_disable_msi,
        .enable_msix = pci_frontend_enable_msix,
        .disable_msix = pci_frontend_disable_msix,
};

static void pci_frontend_registrar(int enable)
{
        if (enable)
                xen_pci_frontend = &pci_frontend_ops;
        else
                xen_pci_frontend = NULL;
};
#else
static inline void pci_frontend_registrar(int enable) { };
#endif /* CONFIG_PCI_MSI */

/* Claim resources for the PCI frontend as-is, backend won't allow changes */
static int pcifront_claim_resource(struct pci_dev *dev, void *data)
{
        struct pcifront_device *pdev = data;
        int i;
        struct resource *r;

        pci_dev_for_each_resource(dev, r, i) {
                if (!r->parent && r->start && r->flags) {
                        dev_info(&pdev->xdev->dev, "claiming resource %s/%d\n",
                                pci_name(dev), i);
                        if (pci_claim_resource(dev, i)) {
                                dev_err(&pdev->xdev->dev, "Could not claim resource %s/%d! "
                                        "Device offline. Try using e820_host=1 in the guest config.\n",
                                        pci_name(dev), i);
                        }
                }
        }

        return 0;
}

static int pcifront_scan_bus(struct pcifront_device *pdev,
                                unsigned int domain, unsigned int bus,
                                struct pci_bus *b)
{
        struct pci_dev *d;
        unsigned int devfn;

        /*
         * Scan the bus for functions and add.
         * We omit handling of PCI bridge attachment because pciback prevents
         * bridges from being exported.
         */
        for (devfn = 0; devfn < 0x100; devfn++) {
                d = pci_get_slot(b, devfn);
                if (d) {
                        /* Device is already known. */
                        pci_dev_put(d);
                        continue;
                }

                d = pci_scan_single_device(b, devfn);
                if (d)
                        dev_info(&pdev->xdev->dev, "New device on "
                                 "%04x:%02x:%02x.%d found.\n", domain, bus,
                                 PCI_SLOT(devfn), PCI_FUNC(devfn));
        }

        return 0;
}

static int pcifront_scan_root(struct pcifront_device *pdev,
                                 unsigned int domain, unsigned int bus)
{
        struct pci_bus *b;
        LIST_HEAD(resources);
        struct pcifront_sd *sd = NULL;
        struct pci_bus_entry *bus_entry = NULL;
        int err = 0;
        static struct resource busn_res = {
                .start = 0,
                .end = 255,
                .flags = IORESOURCE_BUS,
        };

#ifndef CONFIG_PCI_DOMAINS
        if (domain != 0) {
                dev_err(&pdev->xdev->dev,
                        "PCI Root in non-zero PCI Domain! domain=%d\n", domain);
                dev_err(&pdev->xdev->dev,
                        "Please compile with CONFIG_PCI_DOMAINS\n");
                err = -EINVAL;
                goto err_out;
        }
#endif

        dev_info(&pdev->xdev->dev, "Creating PCI Frontend Bus %04x:%02x\n",
                 domain, bus);

        bus_entry = kzalloc_obj(*bus_entry);
        sd = kzalloc_obj(*sd);
        if (!bus_entry || !sd) {
                err = -ENOMEM;
                goto err_out;
        }
        pci_add_resource(&resources, &ioport_resource);
        pci_add_resource(&resources, &iomem_resource);
        pci_add_resource(&resources, &busn_res);
        pcifront_init_sd(sd, domain, bus, pdev);

        pci_lock_rescan_remove();

        b = pci_scan_root_bus(&pdev->xdev->dev, bus,
                                  &pcifront_bus_ops, sd, &resources);
        if (!b) {
                dev_err(&pdev->xdev->dev,
                        "Error creating PCI Frontend Bus!\n");
                err = -ENOMEM;
                pci_unlock_rescan_remove();
                pci_free_resource_list(&resources);
                goto err_out;
        }

        bus_entry->bus = b;

        list_add(&bus_entry->list, &pdev->root_buses);

        /*
         * pci_scan_root_bus skips devices which do not have a
         * devfn==0. The pcifront_scan_bus enumerates all devfn.
         */
        err = pcifront_scan_bus(pdev, domain, bus, b);

        /* Claim resources before going "live" with our devices */
        pci_walk_bus(b, pcifront_claim_resource, pdev);

        /* Create SysFS and notify udev of the devices. Aka: "going live" */
        pci_bus_add_devices(b);

        pci_unlock_rescan_remove();
        return err;

err_out:
        kfree(bus_entry);
        kfree(sd);

        return err;
}

static int pcifront_rescan_root(struct pcifront_device *pdev,
                                   unsigned int domain, unsigned int bus)
{
        int err;
        struct pci_bus *b;

        b = pci_find_bus(domain, bus);
        if (!b)
                /* If the bus is unknown, create it. */
                return pcifront_scan_root(pdev, domain, bus);

        dev_info(&pdev->xdev->dev, "Rescanning PCI Frontend Bus %04x:%02x\n",
                 domain, bus);

        err = pcifront_scan_bus(pdev, domain, bus, b);

        /* Claim resources before going "live" with our devices */
        pci_walk_bus(b, pcifront_claim_resource, pdev);

        /* Create SysFS and notify udev of the devices. Aka: "going live" */
        pci_bus_add_devices(b);

        return err;
}

static void free_root_bus_devs(struct pci_bus *bus)
{
        struct pci_dev *dev;

        while (!list_empty(&bus->devices)) {
                dev = container_of(bus->devices.next, struct pci_dev,
                                   bus_list);
                pci_dbg(dev, "removing device\n");
                pci_stop_and_remove_bus_device(dev);
        }
}

static void pcifront_free_roots(struct pcifront_device *pdev)
{
        struct pci_bus_entry *bus_entry, *t;

        dev_dbg(&pdev->xdev->dev, "cleaning up root buses\n");

        pci_lock_rescan_remove();
        list_for_each_entry_safe(bus_entry, t, &pdev->root_buses, list) {
                list_del(&bus_entry->list);

                free_root_bus_devs(bus_entry->bus);

                kfree(bus_entry->bus->sysdata);

                device_unregister(bus_entry->bus->bridge);
                pci_remove_bus(bus_entry->bus);

                kfree(bus_entry);
        }
        pci_unlock_rescan_remove();
}

static pci_ers_result_t pcifront_common_process(int cmd,
                                                struct pcifront_device *pdev,
                                                pci_channel_state_t state)
{
        struct pci_driver *pdrv;
        int bus = pdev->sh_info->aer_op.bus;
        int devfn = pdev->sh_info->aer_op.devfn;
        int domain = pdev->sh_info->aer_op.domain;
        struct pci_dev *pcidev;

        dev_dbg(&pdev->xdev->dev,
                "pcifront AER process: cmd %x (bus:%x, devfn%x)",
                cmd, bus, devfn);

        pcidev = pci_get_domain_bus_and_slot(domain, bus, devfn);
        if (!pcidev || !pcidev->dev.driver) {
                dev_err(&pdev->xdev->dev, "device or AER driver is NULL\n");
                pci_dev_put(pcidev);
                return PCI_ERS_RESULT_NONE;
        }
        pdrv = to_pci_driver(pcidev->dev.driver);

        if (pdrv->err_handler && pdrv->err_handler->error_detected) {
                pci_dbg(pcidev, "trying to call AER service\n");
                switch (cmd) {
                case XEN_PCI_OP_aer_detected:
                        return pdrv->err_handler->error_detected(pcidev, state);
                case XEN_PCI_OP_aer_mmio:
                        return pdrv->err_handler->mmio_enabled(pcidev);
                case XEN_PCI_OP_aer_slotreset:
                        return pdrv->err_handler->slot_reset(pcidev);
                case XEN_PCI_OP_aer_resume:
                        pdrv->err_handler->resume(pcidev);
                        return PCI_ERS_RESULT_NONE;
                default:
                        dev_err(&pdev->xdev->dev,
                                "bad request in aer recovery operation!\n");
                }
        }

        return PCI_ERS_RESULT_NONE;
}


static void pcifront_do_aer(struct work_struct *data)
{
        struct pcifront_device *pdev =
                container_of(data, struct pcifront_device, op_work);
        int cmd = pdev->sh_info->aer_op.cmd;
        pci_channel_state_t state =
                (pci_channel_state_t)pdev->sh_info->aer_op.err;

        /*
         * If a pci_conf op is in progress, we have to wait until it is done
         * before service aer op
         */
        dev_dbg(&pdev->xdev->dev,
                "pcifront service aer bus %x devfn %x\n",
                pdev->sh_info->aer_op.bus, pdev->sh_info->aer_op.devfn);

        pdev->sh_info->aer_op.err = pcifront_common_process(cmd, pdev, state);

        /* Post the operation to the guest. */
        wmb();
        clear_bit(_XEN_PCIB_active, (unsigned long *)&pdev->sh_info->flags);
        notify_remote_via_evtchn(pdev->evtchn);

        /*in case of we lost an aer request in four lines time_window*/
        smp_mb__before_atomic();
        clear_bit(_PDEVB_op_active, &pdev->flags);
        smp_mb__after_atomic();

        schedule_pcifront_aer_op(pdev);

}

static irqreturn_t pcifront_handler_aer(int irq, void *dev)
{
        struct pcifront_device *pdev = dev;

        schedule_pcifront_aer_op(pdev);
        return IRQ_HANDLED;
}
static int pcifront_connect_and_init_dma(struct pcifront_device *pdev)
{
        int err = 0;

        spin_lock(&pcifront_dev_lock);

        if (!pcifront_dev) {
                dev_info(&pdev->xdev->dev, "Installing PCI frontend\n");
                pcifront_dev = pdev;
        } else
                err = -EEXIST;

        spin_unlock(&pcifront_dev_lock);

        return err;
}

static void pcifront_disconnect(struct pcifront_device *pdev)
{
        spin_lock(&pcifront_dev_lock);

        if (pdev == pcifront_dev) {
                dev_info(&pdev->xdev->dev,
                         "Disconnecting PCI Frontend Buses\n");
                pcifront_dev = NULL;
        }

        spin_unlock(&pcifront_dev_lock);
}
static struct pcifront_device *alloc_pdev(struct xenbus_device *xdev)
{
        struct pcifront_device *pdev;

        pdev = kzalloc_obj(struct pcifront_device);
        if (pdev == NULL)
                goto out;

        if (xenbus_setup_ring(xdev, GFP_KERNEL, (void **)&pdev->sh_info, 1,
                              &pdev->gnt_ref)) {
                kfree(pdev);
                pdev = NULL;
                goto out;
        }
        pdev->sh_info->flags = 0;

        /*Flag for registering PV AER handler*/
        set_bit(_XEN_PCIB_AERHANDLER, (void *)&pdev->sh_info->flags);

        dev_set_drvdata(&xdev->dev, pdev);
        pdev->xdev = xdev;

        INIT_LIST_HEAD(&pdev->root_buses);

        spin_lock_init(&pdev->sh_info_lock);

        pdev->evtchn = INVALID_EVTCHN;
        pdev->irq = -1;

        INIT_WORK(&pdev->op_work, pcifront_do_aer);

        dev_dbg(&xdev->dev, "Allocated pdev @ 0x%p pdev->sh_info @ 0x%p\n",
                pdev, pdev->sh_info);
out:
        return pdev;
}

static void free_pdev(struct pcifront_device *pdev)
{
        dev_dbg(&pdev->xdev->dev, "freeing pdev @ 0x%p\n", pdev);

        pcifront_free_roots(pdev);

        cancel_work_sync(&pdev->op_work);

        if (pdev->irq >= 0)
                unbind_from_irqhandler(pdev->irq, pdev);

        if (pdev->evtchn != INVALID_EVTCHN)
                xenbus_free_evtchn(pdev->xdev, pdev->evtchn);

        xenbus_teardown_ring((void **)&pdev->sh_info, 1, &pdev->gnt_ref);

        dev_set_drvdata(&pdev->xdev->dev, NULL);

        kfree(pdev);
}

static int pcifront_publish_info(struct pcifront_device *pdev)
{
        int err = 0;
        struct xenbus_transaction trans;

        err = xenbus_alloc_evtchn(pdev->xdev, &pdev->evtchn);
        if (err)
                goto out;

        err = bind_evtchn_to_irqhandler(pdev->evtchn, pcifront_handler_aer,
                0, "pcifront", pdev);

        if (err < 0)
                return err;

        pdev->irq = err;

do_publish:
        err = xenbus_transaction_start(&trans);
        if (err) {
                xenbus_dev_fatal(pdev->xdev, err,
                                 "Error writing configuration for backend "
                                 "(start transaction)");
                goto out;
        }

        err = xenbus_printf(trans, pdev->xdev->nodename,
                            "pci-op-ref", "%u", pdev->gnt_ref);
        if (!err)
                err = xenbus_printf(trans, pdev->xdev->nodename,
                                    "event-channel", "%u", pdev->evtchn);
        if (!err)
                err = xenbus_printf(trans, pdev->xdev->nodename,
                                    "magic", XEN_PCI_MAGIC);

        if (err) {
                xenbus_transaction_end(trans, 1);
                xenbus_dev_fatal(pdev->xdev, err,
                                 "Error writing configuration for backend");
                goto out;
        } else {
                err = xenbus_transaction_end(trans, 0);
                if (err == -EAGAIN)
                        goto do_publish;
                else if (err) {
                        xenbus_dev_fatal(pdev->xdev, err,
                                         "Error completing transaction "
                                         "for backend");
                        goto out;
                }
        }

        xenbus_switch_state(pdev->xdev, XenbusStateInitialised);

        dev_dbg(&pdev->xdev->dev, "publishing successful!\n");

out:
        return err;
}

static void pcifront_connect(struct pcifront_device *pdev)
{
        int err;
        int i, num_roots, len;
        char str[64];
        unsigned int domain, bus;

        err = xenbus_scanf(XBT_NIL, pdev->xdev->otherend,
                           "root_num", "%d", &num_roots);
        if (err == -ENOENT) {
                xenbus_dev_error(pdev->xdev, err,
                                 "No PCI Roots found, trying 0000:00");
                err = pcifront_rescan_root(pdev, 0, 0);
                if (err) {
                        xenbus_dev_fatal(pdev->xdev, err,
                                         "Error scanning PCI root 0000:00");
                        return;
                }
                num_roots = 0;
        } else if (err != 1) {
                xenbus_dev_fatal(pdev->xdev, err >= 0 ? -EINVAL : err,
                                 "Error reading number of PCI roots");
                return;
        }

        for (i = 0; i < num_roots; i++) {
                len = snprintf(str, sizeof(str), "root-%d", i);
                if (unlikely(len >= (sizeof(str) - 1)))
                        return;

                err = xenbus_scanf(XBT_NIL, pdev->xdev->otherend, str,
                                   "%x:%x", &domain, &bus);
                if (err != 2) {
                        xenbus_dev_fatal(pdev->xdev, err >= 0 ? -EINVAL : err,
                                         "Error reading PCI root %d", i);
                        return;
                }

                err = pcifront_rescan_root(pdev, domain, bus);
                if (err) {
                        xenbus_dev_fatal(pdev->xdev, err,
                                         "Error scanning PCI root %04x:%02x",
                                         domain, bus);
                        return;
                }
        }

        xenbus_switch_state(pdev->xdev, XenbusStateConnected);
}

static void pcifront_try_connect(struct pcifront_device *pdev)
{
        int err;

        /* Only connect once */
        if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename) !=
            XenbusStateInitialised)
                return;

        err = pcifront_connect_and_init_dma(pdev);
        if (err && err != -EEXIST) {
                xenbus_dev_fatal(pdev->xdev, err,
                                 "Error setting up PCI Frontend");
                return;
        }

        pcifront_connect(pdev);
}

static int pcifront_try_disconnect(struct pcifront_device *pdev)
{
        int err = 0;
        enum xenbus_state prev_state;


        prev_state = xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename);

        if (prev_state >= XenbusStateClosing)
                goto out;

        if (prev_state == XenbusStateConnected) {
                pcifront_free_roots(pdev);
                pcifront_disconnect(pdev);
        }

        err = xenbus_switch_state(pdev->xdev, XenbusStateClosed);

out:

        return err;
}

static void pcifront_attach_devices(struct pcifront_device *pdev)
{
        if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename) ==
            XenbusStateReconfiguring)
                pcifront_connect(pdev);
}

static int pcifront_detach_devices(struct pcifront_device *pdev)
{
        int err = 0;
        int i, num_devs;
        enum xenbus_state state;
        unsigned int domain, bus, slot, func;
        struct pci_dev *pci_dev;
        char str[64];

        state = xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename);
        if (state == XenbusStateInitialised) {
                dev_dbg(&pdev->xdev->dev, "Handle skipped connect.\n");
                /* We missed Connected and need to initialize. */
                err = pcifront_connect_and_init_dma(pdev);
                if (err && err != -EEXIST) {
                        xenbus_dev_fatal(pdev->xdev, err,
                                         "Error setting up PCI Frontend");
                        goto out;
                }

                goto out_switch_state;
        } else if (state != XenbusStateConnected) {
                goto out;
        }

        err = xenbus_scanf(XBT_NIL, pdev->xdev->otherend, "num_devs", "%d",
                           &num_devs);
        if (err != 1) {
                if (err >= 0)
                        err = -EINVAL;
                xenbus_dev_fatal(pdev->xdev, err,
                                 "Error reading number of PCI devices");
                goto out;
        }

        /* Find devices being detached and remove them. */
        for (i = 0; i < num_devs; i++) {
                int l, state;

                l = snprintf(str, sizeof(str), "state-%d", i);
                if (unlikely(l >= (sizeof(str) - 1))) {
                        err = -ENOMEM;
                        goto out;
                }
                state = xenbus_read_unsigned(pdev->xdev->otherend, str,
                                             XenbusStateUnknown);

                if (state != XenbusStateClosing)
                        continue;

                /* Remove device. */
                l = snprintf(str, sizeof(str), "vdev-%d", i);
                if (unlikely(l >= (sizeof(str) - 1))) {
                        err = -ENOMEM;
                        goto out;
                }
                err = xenbus_scanf(XBT_NIL, pdev->xdev->otherend, str,
                                   "%x:%x:%x.%x", &domain, &bus, &slot, &func);
                if (err != 4) {
                        if (err >= 0)
                                err = -EINVAL;
                        xenbus_dev_fatal(pdev->xdev, err,
                                         "Error reading PCI device %d", i);
                        goto out;
                }

                pci_dev = pci_get_domain_bus_and_slot(domain, bus,
                                PCI_DEVFN(slot, func));
                if (!pci_dev) {
                        dev_dbg(&pdev->xdev->dev,
                                "Cannot get PCI device %04x:%02x:%02x.%d\n",
                                domain, bus, slot, func);
                        continue;
                }
                pci_lock_rescan_remove();
                pci_stop_and_remove_bus_device(pci_dev);
                pci_dev_put(pci_dev);
                pci_unlock_rescan_remove();

                dev_dbg(&pdev->xdev->dev,
                        "PCI device %04x:%02x:%02x.%d removed.\n",
                        domain, bus, slot, func);
        }

 out_switch_state:
        err = xenbus_switch_state(pdev->xdev, XenbusStateReconfiguring);

out:
        return err;
}

static void pcifront_backend_changed(struct xenbus_device *xdev,
                                                  enum xenbus_state be_state)
{
        struct pcifront_device *pdev = dev_get_drvdata(&xdev->dev);

        switch (be_state) {
        case XenbusStateUnknown:
        case XenbusStateInitialising:
        case XenbusStateInitWait:
        case XenbusStateInitialised:
                break;

        case XenbusStateConnected:
                pcifront_try_connect(pdev);
                break;

        case XenbusStateClosed:
                if (xdev->state == XenbusStateClosed)
                        break;
                fallthrough;    /* Missed the backend's CLOSING state */
        case XenbusStateClosing:
                dev_warn(&xdev->dev, "backend going away!\n");
                pcifront_try_disconnect(pdev);
                break;

        case XenbusStateReconfiguring:
                pcifront_detach_devices(pdev);
                break;

        case XenbusStateReconfigured:
                pcifront_attach_devices(pdev);
                break;
        }
}

static int pcifront_xenbus_probe(struct xenbus_device *xdev,
                                 const struct xenbus_device_id *id)
{
        int err = 0;
        struct pcifront_device *pdev = alloc_pdev(xdev);

        if (pdev == NULL) {
                err = -ENOMEM;
                xenbus_dev_fatal(xdev, err,
                                 "Error allocating pcifront_device struct");
                goto out;
        }

        err = pcifront_publish_info(pdev);
        if (err)
                free_pdev(pdev);

out:
        return err;
}

static void pcifront_xenbus_remove(struct xenbus_device *xdev)
{
        struct pcifront_device *pdev = dev_get_drvdata(&xdev->dev);

        if (pdev)
                free_pdev(pdev);
}

static const struct xenbus_device_id xenpci_ids[] = {
        {"pci"},
        {""},
};

static struct xenbus_driver xenpci_driver = {
        .name                   = "pcifront",
        .ids                    = xenpci_ids,
        .probe                  = pcifront_xenbus_probe,
        .remove                 = pcifront_xenbus_remove,
        .otherend_changed       = pcifront_backend_changed,
};

static int __init pcifront_init(void)
{
        if (!xen_pv_domain() || xen_initial_domain())
                return -ENODEV;

        if (!xen_has_pv_devices())
                return -ENODEV;

        pci_frontend_registrar(1 /* enable */);

        return xenbus_register_frontend(&xenpci_driver);
}

static void __exit pcifront_cleanup(void)
{
        xenbus_unregister_driver(&xenpci_driver);
        pci_frontend_registrar(0 /* disable */);
}
module_init(pcifront_init);
module_exit(pcifront_cleanup);

MODULE_DESCRIPTION("Xen PCI passthrough frontend.");
MODULE_LICENSE("GPL");
MODULE_ALIAS("xen:pci");