path: root/drivers/pci/pcie/aer/aerdrv_core.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Implement the core part of PCIe AER. When a PCIe error is delivered, an
 * error message will be collected and printed to console, then an error
 * recovery procedure will be executed by following the PCI error recovery
 * rules.
 *
 * Copyright (C) 2006 Intel Corp.
 *	Tom Long Nguyen (tom.l.nguyen@intel.com)
 *	Zhang Yanmin (yanmin.zhang@intel.com)
 */

#include <linux/module.h>
#include <linux/pci.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/pm.h>
#include <linux/suspend.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/kfifo.h>
#include "aerdrv.h"

#define	PCI_EXP_AER_FLAGS	(PCI_EXP_DEVCTL_CERE | PCI_EXP_DEVCTL_NFERE | \
				 PCI_EXP_DEVCTL_FERE | PCI_EXP_DEVCTL_URRE)

int pci_enable_pcie_error_reporting(struct pci_dev *dev)
{
	if (pcie_aer_get_firmware_first(dev))
		return -EIO;

	if (!dev->aer_cap)
		return -EIO;

	return pcie_capability_set_word(dev, PCI_EXP_DEVCTL, PCI_EXP_AER_FLAGS);
}
EXPORT_SYMBOL_GPL(pci_enable_pcie_error_reporting);

int pci_disable_pcie_error_reporting(struct pci_dev *dev)
{
	if (pcie_aer_get_firmware_first(dev))
		return -EIO;

	return pcie_capability_clear_word(dev, PCI_EXP_DEVCTL,
					  PCI_EXP_AER_FLAGS);
}
EXPORT_SYMBOL_GPL(pci_disable_pcie_error_reporting);

int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
{
	int pos;
	u32 status;

	pos = dev->aer_cap;
	if (!pos)
		return -EIO;

	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
	if (status)
		pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);

	return 0;
}
EXPORT_SYMBOL_GPL(pci_cleanup_aer_uncorrect_error_status);

int pci_cleanup_aer_error_status_regs(struct pci_dev *dev)
{
	int pos;
	u32 status;
	int port_type;

	if (!pci_is_pcie(dev))
		return -ENODEV;

	pos = dev->aer_cap;
	if (!pos)
		return -EIO;

	port_type = pci_pcie_type(dev);
	if (port_type == PCI_EXP_TYPE_ROOT_PORT) {
		pci_read_config_dword(dev, pos + PCI_ERR_ROOT_STATUS, &status);
		pci_write_config_dword(dev, pos + PCI_ERR_ROOT_STATUS, status);
	}

	pci_read_config_dword(dev, pos + PCI_ERR_COR_STATUS, &status);
	pci_write_config_dword(dev, pos + PCI_ERR_COR_STATUS, status);

	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
	pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);

	return 0;
}

int pci_aer_init(struct pci_dev *dev)
{
	dev->aer_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ERR);
	return pci_cleanup_aer_error_status_regs(dev);
}

/**
 * add_error_device - list device to be handled
 * @e_info: pointer to error info
 * @dev: pointer to pci_dev to be added
 */
static int add_error_device(struct aer_err_info *e_info, struct pci_dev *dev)
{
	if (e_info->error_dev_num < AER_MAX_MULTI_ERR_DEVICES) {
		e_info->dev[e_info->error_dev_num] = dev;
		e_info->error_dev_num++;
		return 0;
	}
	return -ENOSPC;
}

/**
 * is_error_source - check whether the device is source of reported error
 * @dev: pointer to pci_dev to be checked
 * @e_info: pointer to reported error info
 */
static bool is_error_source(struct pci_dev *dev, struct aer_err_info *e_info)
{
	int pos;
	u32 status, mask;
	u16 reg16;

	/*
	 * When bus id is equal to 0, it might be a bad id
	 * reported by root port.
	 */
	if ((PCI_BUS_NUM(e_info->id) != 0) &&
	    !(dev->bus->bus_flags & PCI_BUS_FLAGS_NO_AERSID)) {
		/* Device ID match? */
		if (e_info->id == ((dev->bus->number << 8) | dev->devfn))
			return true;

		/* Continue id comparing if there is no multiple error */
		if (!e_info->multi_error_valid)
			return false;
	}

	/*
	 * When either
	 *      1) bus id is equal to 0. Some ports might lose the bus
	 *              id of error source id;
	 *      2) bus flag PCI_BUS_FLAGS_NO_AERSID is set
	 *      3) There are multiple errors and prior ID comparing fails;
	 * We check AER status registers to find possible reporter.
	 */
	if (atomic_read(&dev->enable_cnt) == 0)
		return false;

	/* Check if AER is enabled */
	pcie_capability_read_word(dev, PCI_EXP_DEVCTL, &reg16);
	if (!(reg16 & PCI_EXP_AER_FLAGS))
		return false;

	pos = dev->aer_cap;
	if (!pos)
		return false;

	/* Check if error is recorded */
	if (e_info->severity == AER_CORRECTABLE) {
		pci_read_config_dword(dev, pos + PCI_ERR_COR_STATUS, &status);
		pci_read_config_dword(dev, pos + PCI_ERR_COR_MASK, &mask);
	} else {
		pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
		pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_MASK, &mask);
	}
	if (status & ~mask)
		return true;

	return false;
}

static int find_device_iter(struct pci_dev *dev, void *data)
{
	struct aer_err_info *e_info = (struct aer_err_info *)data;

	if (is_error_source(dev, e_info)) {
		/* List this device */
		if (add_error_device(e_info, dev)) {
			/* We cannot handle more... Stop iteration */
			/* TODO: Should print error message here? */
			return 1;
		}

		/* If there is only a single error, stop iteration */
		if (!e_info->multi_error_valid)
			return 1;
	}
	return 0;
}

/**
 * find_source_device - search through device hierarchy for source device
 * @parent: pointer to Root Port pci_dev data structure
 * @e_info: including detailed error information such like id
 *
 * Return true if found.
 *
 * Invoked by DPC when error is detected at the Root Port.
 * Caller of this function must set id, severity, and multi_error_valid of
 * struct aer_err_info pointed by @e_info properly.  This function must fill
 * e_info->error_dev_num and e_info->dev[], based on the given information.
 */
static bool find_source_device(struct pci_dev *parent,
		struct aer_err_info *e_info)
{
	struct pci_dev *dev = parent;
	int result;

	/* Must reset in this function */
	e_info->error_dev_num = 0;

	/* Is Root Port an agent that sends error message? */
	result = find_device_iter(dev, e_info);
	if (result)
		return true;

	pci_walk_bus(parent->subordinate, find_device_iter, e_info);

	if (!e_info->error_dev_num) {
		pci_printk(KERN_DEBUG, parent, "can't find device of ID%04x\n",
			   e_info->id);
		return false;
	}
	return true;
}

static int report_error_detected(struct pci_dev *dev, void *data)
{
	pci_ers_result_t vote;
	const struct pci_error_handlers *err_handler;
	struct aer_broadcast_data *result_data;
	result_data = (struct aer_broadcast_data *) data;

	device_lock(&dev->dev);
	dev->error_state = result_data->state;

	if (!dev->driver ||
		!dev->driver->err_handler ||
		!dev->driver->err_handler->error_detected) {
		if (result_data->state == pci_channel_io_frozen &&
			dev->hdr_type != PCI_HEADER_TYPE_BRIDGE) {
			/*
			 * In case of fatal recovery, if one of down-
			 * stream device has no driver. We might be
			 * unable to recover because a later insmod
			 * of a driver for this device is unaware of
			 * its hw state.
			 */
			pci_printk(KERN_DEBUG, dev, "device has %s\n",
				   dev->driver ?
				   "no AER-aware driver" : "no driver");
		}

		/*
		 * If there's any device in the subtree that does not
		 * have an error_detected callback, returning
		 * PCI_ERS_RESULT_NO_AER_DRIVER prevents calling of
		 * the subsequent mmio_enabled/slot_reset/resume
		 * callbacks of "any" device in the subtree. All the
		 * devices in the subtree are left in the error state
		 * without recovery.
		 */

		if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
			vote = PCI_ERS_RESULT_NO_AER_DRIVER;
		else
			vote = PCI_ERS_RESULT_NONE;
	} else {
		err_handler = dev->driver->err_handler;
		vote = err_handler->error_detected(dev, result_data->state);
		pci_uevent_ers(dev, PCI_ERS_RESULT_NONE);
	}

	result_data->result = merge_result(result_data->result, vote);
	device_unlock(&dev->dev);
	return 0;
}

static int report_mmio_enabled(struct pci_dev *dev, void *data)
{
	pci_ers_result_t vote;
	const struct pci_error_handlers *err_handler;
	struct aer_broadcast_data *result_data;
	result_data = (struct aer_broadcast_data *) data;

	device_lock(&dev->dev);
	if (!dev->driver ||
		!dev->driver->err_handler ||
		!dev->driver->err_handler->mmio_enabled)
		goto out;

	err_handler = dev->driver->err_handler;
	vote = err_handler->mmio_enabled(dev);
	result_data->result = merge_result(result_data->result, vote);
out:
	device_unlock(&dev->dev);
	return 0;
}

static int report_slot_reset(struct pci_dev *dev, void *data)
{
	pci_ers_result_t vote;
	const struct pci_error_handlers *err_handler;
	struct aer_broadcast_data *result_data;
	result_data = (struct aer_broadcast_data *) data;

	device_lock(&dev->dev);
	if (!dev->driver ||
		!dev->driver->err_handler ||
		!dev->driver->err_handler->slot_reset)
		goto out;

	err_handler = dev->driver->err_handler;
	vote = err_handler->slot_reset(dev);
	result_data->result = merge_result(result_data->result, vote);
out:
	device_unlock(&dev->dev);
	return 0;
}

static int report_resume(struct pci_dev *dev, void *data)
{
	const struct pci_error_handlers *err_handler;

	device_lock(&dev->dev);
	dev->error_state = pci_channel_io_normal;

	if (!dev->driver ||
		!dev->driver->err_handler ||
		!dev->driver->err_handler->resume)
		goto out;

	err_handler = dev->driver->err_handler;
	err_handler->resume(dev);
	pci_uevent_ers(dev, PCI_ERS_RESULT_RECOVERED);
out:
	device_unlock(&dev->dev);
	return 0;
}

/**
 * broadcast_error_message - handle message broadcast to downstream drivers
 * @dev: pointer to from where in a hierarchy message is broadcasted down
 * @state: error state
 * @error_mesg: message to print
 * @cb: callback to be broadcasted
 *
 * Invoked during error recovery process. Once being invoked, the content
 * of error severity will be broadcasted to all downstream drivers in a
 * hierarchy in question.
 */
static pci_ers_result_t broadcast_error_message(struct pci_dev *dev,
	enum pci_channel_state state,
	char *error_mesg,
	int (*cb)(struct pci_dev *, void *))
{
	struct aer_broadcast_data result_data;

	pci_printk(KERN_DEBUG, dev, "broadcast %s message\n", error_mesg);
	result_data.state = state;
	if (cb == report_error_detected)
		result_data.result = PCI_ERS_RESULT_CAN_RECOVER;
	else
		result_data.result = PCI_ERS_RESULT_RECOVERED;

	if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
		/*
		 * If the error is reported by a bridge, we think this error
		 * is related to the downstream link of the bridge, so we
		 * do error recovery on all subordinates of the bridge instead
		 * of the bridge and clear the error status of the bridge.
		 */
		if (cb == report_error_detected)
			dev->error_state = state;
		pci_walk_bus(dev->subordinate, cb, &result_data);
		if (cb == report_resume) {
			pci_cleanup_aer_uncorrect_error_status(dev);
			dev->error_state = pci_channel_io_normal;
		}
	} else {
		/*
		 * If the error is reported by an end point, we think this
		 * error is related to the upstream link of the end point.
		 */
		if (state == pci_channel_io_normal)
			/*
			 * the error is non fatal so the bus is ok, just invoke
			 * the callback for the function that logged the error.
			 */
			cb(dev, &result_data);
		else
			pci_walk_bus(dev->bus, cb, &result_data);
	}

	return result_data.result;
}

/**
 * default_reset_link - default reset function
 * @dev: pointer to pci_dev data structure
 *
 * Invoked when performing link reset on a Downstream Port or a
 * Root Port with no aer driver.
 */
static pci_ers_result_t default_reset_link(struct pci_dev *dev)
{
	pci_reset_bridge_secondary_bus(dev);
	pci_printk(KERN_DEBUG, dev, "downstream link has been reset\n");
	return PCI_ERS_RESULT_RECOVERED;
}

static int find_aer_service_iter(struct device *device, void *data)
{
	struct pcie_port_service_driver *service_driver, **drv;

	drv = (struct pcie_port_service_driver **) data;

	if (device->bus == &pcie_port_bus_type && device->driver) {
		service_driver = to_service_driver(device->driver);
		if (service_driver->service == PCIE_PORT_SERVICE_AER) {
			*drv = service_driver;
			return 1;
		}
	}

	return 0;
}

static struct pcie_port_service_driver *find_aer_service(struct pci_dev *dev)
{
	struct pcie_port_service_driver *drv = NULL;

	device_for_each_child(&dev->dev, &drv, find_aer_service_iter);

	return drv;
}

static pci_ers_result_t reset_link(struct pci_dev *dev)
{
	struct pci_dev *udev;
	pci_ers_result_t status;
	struct pcie_port_service_driver *driver;

	if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
		/* Reset this port for all subordinates */
		udev = dev;
	} else {
		/* Reset the upstream component (likely downstream port) */
		udev = dev->bus->self;
	}

	/* Use the aer driver of the component firstly */
	driver = find_aer_service(udev);

	if (driver && driver->reset_link) {
		status = driver->reset_link(udev);
	} else if (udev->has_secondary_link) {
		status = default_reset_link(udev);
	} else {
		pci_printk(KERN_DEBUG, dev, "no link-reset support at upstream device %s\n",
			pci_name(udev));
		return PCI_ERS_RESULT_DISCONNECT;
	}

	if (status != PCI_ERS_RESULT_RECOVERED) {
		pci_printk(KERN_DEBUG, dev, "link reset at upstream device %s failed\n",
			pci_name(udev));
		return PCI_ERS_RESULT_DISCONNECT;
	}

	return status;
}

/**
 * do_recovery - handle nonfatal/fatal error recovery process
 * @dev: pointer to a pci_dev data structure of agent detecting an error
 * @severity: error severity type
 *
 * Invoked when an error is nonfatal/fatal. Once being invoked, broadcast
 * error detected message to all downstream drivers within a hierarchy in
 * question and return the returned code.
 */
static void do_recovery(struct pci_dev *dev, int severity)
{
	pci_ers_result_t status, result = PCI_ERS_RESULT_RECOVERED;
	enum pci_channel_state state;

	if (severity == AER_FATAL)
		state = pci_channel_io_frozen;
	else
		state = pci_channel_io_normal;

	status = broadcast_error_message(dev,
			state,
			"error_detected",
			report_error_detected);

	if (severity == AER_FATAL) {
		result = reset_link(dev);
		if (result != PCI_ERS_RESULT_RECOVERED)
			goto failed;
	}

	if (status == PCI_ERS_RESULT_CAN_RECOVER)
		status = broadcast_error_message(dev,
				state,
				"mmio_enabled",
				report_mmio_enabled);

	if (status == PCI_ERS_RESULT_NEED_RESET) {
		/*
		 * TODO: Should call platform-specific
		 * functions to reset slot before calling
		 * drivers' slot_reset callbacks?
		 */
		status = broadcast_error_message(dev,
				state,
				"slot_reset",
				report_slot_reset);
	}

	if (status != PCI_ERS_RESULT_RECOVERED)
		goto failed;

	broadcast_error_message(dev,
				state,
				"resume",
				report_resume);

	pci_info(dev, "AER: Device recovery successful\n");
	return;

failed:
	pci_uevent_ers(dev, PCI_ERS_RESULT_DISCONNECT);
	/* TODO: Should kernel panic here? */
	pci_info(dev, "AER: Device recovery failed\n");
}

/**
 * handle_error_source - handle logging error into an event log
 * @aerdev: pointer to pcie_device data structure of the root port
 * @dev: pointer to pci_dev data structure of error source device
 * @info: comprehensive error information
 *
 * Invoked when an error being detected by Root Port.
 */
static void handle_error_source(struct pcie_device *aerdev,
	struct pci_dev *dev,
	struct aer_err_info *info)
{
	int pos;

	if (info->severity == AER_CORRECTABLE) {
		/*
		 * Correctable error does not need software intervention.
		 * No need to go through error recovery process.
		 */
		pos = dev->aer_cap;
		if (pos)
			pci_write_config_dword(dev, pos + PCI_ERR_COR_STATUS,
					info->status);
	} else
		do_recovery(dev, info->severity);
}

#ifdef CONFIG_ACPI_APEI_PCIEAER
static void aer_recover_work_func(struct work_struct *work);

#define AER_RECOVER_RING_ORDER		4
#define AER_RECOVER_RING_SIZE		(1 << AER_RECOVER_RING_ORDER)

struct aer_recover_entry {
	u8	bus;
	u8	devfn;
	u16	domain;
	int	severity;
	struct aer_capability_regs *regs;
};

static DEFINE_KFIFO(aer_recover_ring, struct aer_recover_entry,
		    AER_RECOVER_RING_SIZE);
/*
 * Mutual exclusion for writers of aer_recover_ring, reader side don't
 * need lock, because there is only one reader and lock is not needed
 * between reader and writer.
 */
static DEFINE_SPINLOCK(aer_recover_ring_lock);
static DECLARE_WORK(aer_recover_work, aer_recover_work_func);

void aer_recover_queue(int domain, unsigned int bus, unsigned int devfn,
		       int severity, struct aer_capability_regs *aer_regs)
{
	unsigned long flags;
	struct aer_recover_entry entry = {
		.bus		= bus,
		.devfn		= devfn,
		.domain		= domain,
		.severity	= severity,
		.regs		= aer_regs,
	};

	spin_lock_irqsave(&aer_recover_ring_lock, flags);
	if (kfifo_put(&aer_recover_ring, entry))
		schedule_work(&aer_recover_work);
	else
		pr_err("AER recover: Buffer overflow when recovering AER for %04x:%02x:%02x:%x\n",
		       domain, bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
	spin_unlock_irqrestore(&aer_recover_ring_lock, flags);
}
EXPORT_SYMBOL_GPL(aer_recover_queue);

static void aer_recover_work_func(struct work_struct *work)
{
	struct aer_recover_entry entry;
	struct pci_dev *pdev;

	while (kfifo_get(&aer_recover_ring, &entry)) {
		pdev = pci_get_domain_bus_and_slot(entry.domain, entry.bus,
						   entry.devfn);
		if (!pdev) {
			pr_err("AER recover: Can not find pci_dev for %04x:%02x:%02x:%x\n",
			       entry.domain, entry.bus,
			       PCI_SLOT(entry.devfn), PCI_FUNC(entry.devfn));
			continue;
		}
		cper_print_aer(pdev, entry.severity, entry.regs);
		if (entry.severity != AER_CORRECTABLE)
			do_recovery(pdev, entry.severity);
		pci_dev_put(pdev);
	}
}
#endif

/**
 * get_device_error_info - read error status from dev and store it to info
 * @dev: pointer to the device expected to have a error record
 * @info: pointer to structure to store the error record
 *
 * Return 1 on success, 0 on error.
 *
 * Note that @info is reused among all error devices. Clear fields properly.
 */
static int get_device_error_info(struct pci_dev *dev, struct aer_err_info *info)
{
	int pos, temp;

	/* Must reset in this function */
	info->status = 0;
	info->tlp_header_valid = 0;

	pos = dev->aer_cap;

	/* The device might not support AER */
	if (!pos)
		return 0;

	if (info->severity == AER_CORRECTABLE) {
		pci_read_config_dword(dev, pos + PCI_ERR_COR_STATUS,
			&info->status);
		pci_read_config_dword(dev, pos + PCI_ERR_COR_MASK,
			&info->mask);
		if (!(info->status & ~info->mask))
			return 0;
	} else if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE ||
		info->severity == AER_NONFATAL) {

		/* Link is still healthy for IO reads */
		pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS,
			&info->status);
		pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_MASK,
			&info->mask);
		if (!(info->status & ~info->mask))
			return 0;

		/* Get First Error Pointer */
		pci_read_config_dword(dev, pos + PCI_ERR_CAP, &temp);
		info->first_error = PCI_ERR_CAP_FEP(temp);

		if (info->status & AER_LOG_TLP_MASKS) {
			info->tlp_header_valid = 1;
			pci_read_config_dword(dev,
				pos + PCI_ERR_HEADER_LOG, &info->tlp.dw0);
			pci_read_config_dword(dev,
				pos + PCI_ERR_HEADER_LOG + 4, &info->tlp.dw1);
			pci_read_config_dword(dev,
				pos + PCI_ERR_HEADER_LOG + 8, &info->tlp.dw2);
			pci_read_config_dword(dev,
				pos + PCI_ERR_HEADER_LOG + 12, &info->tlp.dw3);
		}
	}

	return 1;
}

static inline void aer_process_err_devices(struct pcie_device *p_device,
			struct aer_err_info *e_info)
{
	int i;

	/* Report all before handle them, not to lost records by reset etc. */
	for (i = 0; i < e_info->error_dev_num && e_info->dev[i]; i++) {
		if (get_device_error_info(e_info->dev[i], e_info))
			aer_print_error(e_info->dev[i], e_info);
	}
	for (i = 0; i < e_info->error_dev_num && e_info->dev[i]; i++) {
		if (get_device_error_info(e_info->dev[i], e_info))
			handle_error_source(p_device, e_info->dev[i], e_info);
	}
}

/**
 * aer_isr_one_error - consume an error detected by root port
 * @p_device: pointer to error root port service device
 * @e_src: pointer to an error source
 */
static void aer_isr_one_error(struct pcie_device *p_device,
		struct aer_err_source *e_src)
{
	struct aer_rpc *rpc = get_service_data(p_device);
	struct aer_err_info *e_info = &rpc->e_info;

	/*
	 * There is a possibility that both correctable error and
	 * uncorrectable error being logged. Report correctable error first.
	 */
	if (e_src->status & PCI_ERR_ROOT_COR_RCV) {
		e_info->id = ERR_COR_ID(e_src->id);
		e_info->severity = AER_CORRECTABLE;

		if (e_src->status & PCI_ERR_ROOT_MULTI_COR_RCV)
			e_info->multi_error_valid = 1;
		else
			e_info->multi_error_valid = 0;

		aer_print_port_info(p_device->port, e_info);

		if (find_source_device(p_device->port, e_info))
			aer_process_err_devices(p_device, e_info);
	}

	if (e_src->status & PCI_ERR_ROOT_UNCOR_RCV) {
		e_info->id = ERR_UNCOR_ID(e_src->id);

		if (e_src->status & PCI_ERR_ROOT_FATAL_RCV)
			e_info->severity = AER_FATAL;
		else
			e_info->severity = AER_NONFATAL;

		if (e_src->status & PCI_ERR_ROOT_MULTI_UNCOR_RCV)
			e_info->multi_error_valid = 1;
		else
			e_info->multi_error_valid = 0;

		aer_print_port_info(p_device->port, e_info);

		if (find_source_device(p_device->port, e_info))
			aer_process_err_devices(p_device, e_info);
	}
}

/**
 * get_e_source - retrieve an error source
 * @rpc: pointer to the root port which holds an error
 * @e_src: pointer to store retrieved error source
 *
 * Return 1 if an error source is retrieved, otherwise 0.
 *
 * Invoked by DPC handler to consume an error.
 */
static int get_e_source(struct aer_rpc *rpc, struct aer_err_source *e_src)
{
	unsigned long flags;

	/* Lock access to Root error producer/consumer index */
	spin_lock_irqsave(&rpc->e_lock, flags);
	if (rpc->prod_idx == rpc->cons_idx) {
		spin_unlock_irqrestore(&rpc->e_lock, flags);
		return 0;
	}

	*e_src = rpc->e_sources[rpc->cons_idx];
	rpc->cons_idx++;
	if (rpc->cons_idx == AER_ERROR_SOURCES_MAX)
		rpc->cons_idx = 0;
	spin_unlock_irqrestore(&rpc->e_lock, flags);

	return 1;
}

/**
 * aer_isr - consume errors detected by root port
 * @work: definition of this work item
 *
 * Invoked, as DPC, when root port records new detected error
 */
void aer_isr(struct work_struct *work)
{
	struct aer_rpc *rpc = container_of(work, struct aer_rpc, dpc_handler);
	struct pcie_device *p_device = rpc->rpd;
	struct aer_err_source uninitialized_var(e_src);

	mutex_lock(&rpc->rpc_mutex);
	while (get_e_source(rpc, &e_src))
		aer_isr_one_error(p_device, &e_src);
	mutex_unlock(&rpc->rpc_mutex);
}