// SPDX-License-Identifier: GPL-2.0
/*
 * Memory subsystem support
 *
 * Written by Matt Tolentino <matthew.e.tolentino@intel.com>
 *            Dave Hansen <haveblue@us.ibm.com>
 *
 * This file provides the necessary infrastructure to represent
 * a SPARSEMEM-memory-model system's physical memory in /sysfs.
 * All arch-independent code that assumes MEMORY_HOTPLUG requires
 * SPARSEMEM should be contained here, or in mm/memory_hotplug.c.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/topology.h>
#include <linux/capability.h>
#include <linux/device.h>
#include <linux/memory.h>
#include <linux/memory_hotplug.h>
#include <linux/mm.h>
#include <linux/stat.h>
#include <linux/slab.h>

#include <linux/atomic.h>
#include <linux/uaccess.h>

#define MEMORY_CLASS_NAME       "memory"

#define to_memory_block(dev) container_of(dev, struct memory_block, dev)

static int sections_per_block;

static inline unsigned long base_memory_block_id(unsigned long section_nr)
{
        return section_nr / sections_per_block;
}

static inline unsigned long pfn_to_block_id(unsigned long pfn)
{
        return base_memory_block_id(pfn_to_section_nr(pfn));
}

static inline unsigned long phys_to_block_id(unsigned long phys)
{
        return pfn_to_block_id(PFN_DOWN(phys));
}

static int memory_subsys_online(struct device *dev);
static int memory_subsys_offline(struct device *dev);

static struct bus_type memory_subsys = {
        .name = MEMORY_CLASS_NAME,
        .dev_name = MEMORY_CLASS_NAME,
        .online = memory_subsys_online,
        .offline = memory_subsys_offline,
};

static BLOCKING_NOTIFIER_HEAD(memory_chain);

int register_memory_notifier(struct notifier_block *nb)
{
        return blocking_notifier_chain_register(&memory_chain, nb);
}
EXPORT_SYMBOL(register_memory_notifier);

void unregister_memory_notifier(struct notifier_block *nb)
{
        blocking_notifier_chain_unregister(&memory_chain, nb);
}
EXPORT_SYMBOL(unregister_memory_notifier);

static ATOMIC_NOTIFIER_HEAD(memory_isolate_chain);

int register_memory_isolate_notifier(struct notifier_block *nb)
{
        return atomic_notifier_chain_register(&memory_isolate_chain, nb);
}
EXPORT_SYMBOL(register_memory_isolate_notifier);

void unregister_memory_isolate_notifier(struct notifier_block *nb)
{
        atomic_notifier_chain_unregister(&memory_isolate_chain, nb);
}
EXPORT_SYMBOL(unregister_memory_isolate_notifier);

static void memory_block_release(struct device *dev)
{
        struct memory_block *mem = to_memory_block(dev);

        kfree(mem);
}

unsigned long __weak memory_block_size_bytes(void)
{
        return MIN_MEMORY_BLOCK_SIZE;
}
EXPORT_SYMBOL_GPL(memory_block_size_bytes);

/*
 * Show the first physical section index (number) of this memory block.
 */
static ssize_t phys_index_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct memory_block *mem = to_memory_block(dev);
        unsigned long phys_index;

        phys_index = mem->start_section_nr / sections_per_block;
        return sprintf(buf, "%08lx\n", phys_index);
}

/*
 * Show whether the memory block is likely to be offlineable (or is already
 * offline). Once offline, the memory block could be removed. The return
 * value does, however, not indicate that there is a way to remove the
 * memory block.
 */
static ssize_t removable_show(struct device *dev, struct device_attribute *attr,
                              char *buf)
{
        struct memory_block *mem = to_memory_block(dev);
        unsigned long pfn;
        int ret = 1, i;

        if (mem->state != MEM_ONLINE)
                goto out;

        for (i = 0; i < sections_per_block; i++) {
                if (!present_section_nr(mem->start_section_nr + i))
                        continue;
                pfn = section_nr_to_pfn(mem->start_section_nr + i);
                ret &= is_mem_section_removable(pfn, PAGES_PER_SECTION);
        }

out:
        return sprintf(buf, "%d\n", ret);
}

/*
 * online, offline, going offline, etc.
 */
static ssize_t state_show(struct device *dev, struct device_attribute *attr,
                          char *buf)
{
        struct memory_block *mem = to_memory_block(dev);
        ssize_t len = 0;

        /*
         * We can probably put these states in a nice little array
         * so that they're not open-coded
         */
        switch (mem->state) {
        case MEM_ONLINE:
                len = sprintf(buf, "online\n");
                break;
        case MEM_OFFLINE:
                len = sprintf(buf, "offline\n");
                break;
        case MEM_GOING_OFFLINE:
                len = sprintf(buf, "going-offline\n");
                break;
        default:
                len = sprintf(buf, "ERROR-UNKNOWN-%ld\n",
                                mem->state);
                WARN_ON(1);
                break;
        }

        return len;
}

int memory_notify(unsigned long val, void *v)
{
        return blocking_notifier_call_chain(&memory_chain, val, v);
}

int memory_isolate_notify(unsigned long val, void *v)
{
        return atomic_notifier_call_chain(&memory_isolate_chain, val, v);
}

/*
 * The probe routines leave the pages uninitialized, just as the bootmem code
 * does. Make sure we do not access them, but instead use only information from
 * within sections.
 */
static bool pages_correctly_probed(unsigned long start_pfn)
{
        unsigned long section_nr = pfn_to_section_nr(start_pfn);
        unsigned long section_nr_end = section_nr + sections_per_block;
        unsigned long pfn = start_pfn;

        /*
         * memmap between sections is not contiguous except with
         * SPARSEMEM_VMEMMAP. We lookup the page once per section
         * and assume memmap is contiguous within each section
         */
        for (; section_nr < section_nr_end; section_nr++) {
                if (WARN_ON_ONCE(!pfn_valid(pfn)))
                        return false;

                if (!present_section_nr(section_nr)) {
                        pr_warn("section %ld pfn[%lx, %lx) not present\n",
                                section_nr, pfn, pfn + PAGES_PER_SECTION);
                        return false;
                } else if (!valid_section_nr(section_nr)) {
                        pr_warn("section %ld pfn[%lx, %lx) no valid memmap\n",
                                section_nr, pfn, pfn + PAGES_PER_SECTION);
                        return false;
                } else if (online_section_nr(section_nr)) {
                        pr_warn("section %ld pfn[%lx, %lx) is already online\n",
                                section_nr, pfn, pfn + PAGES_PER_SECTION);
                        return false;
                }
                pfn += PAGES_PER_SECTION;
        }

        return true;
}

/*
 * MEMORY_HOTPLUG depends on SPARSEMEM in mm/Kconfig, so it is
 * OK to have direct references to sparsemem variables in here.
 */
static int
memory_block_action(unsigned long start_section_nr, unsigned long action,
                    int online_type)
{
        unsigned long start_pfn;
        unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
        int ret;

        start_pfn = section_nr_to_pfn(start_section_nr);

        switch (action) {
        case MEM_ONLINE:
                if (!pages_correctly_probed(start_pfn))
                        return -EBUSY;

                ret = online_pages(start_pfn, nr_pages, online_type);
                break;
        case MEM_OFFLINE:
                ret = offline_pages(start_pfn, nr_pages);
                break;
        default:
                WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: "
                     "%ld\n", __func__, start_section_nr, action, action);
                ret = -EINVAL;
        }

        return ret;
}

static int memory_block_change_state(struct memory_block *mem,
                unsigned long to_state, unsigned long from_state_req)
{
        int ret = 0;

        if (mem->state != from_state_req)
                return -EINVAL;

        if (to_state == MEM_OFFLINE)
                mem->state = MEM_GOING_OFFLINE;

        ret = memory_block_action(mem->start_section_nr, to_state,
                                mem->online_type);

        mem->state = ret ? from_state_req : to_state;

        return ret;
}

/* The device lock serializes operations on memory_subsys_[online|offline] */
static int memory_subsys_online(struct device *dev)
{
        struct memory_block *mem = to_memory_block(dev);
        int ret;

        if (mem->state == MEM_ONLINE)
                return 0;

        /*
         * If we are called from state_store(), online_type will be
         * set >= 0 Otherwise we were called from the device online
         * attribute and need to set the online_type.
         */
        if (mem->online_type < 0)
                mem->online_type = MMOP_ONLINE_KEEP;

        ret = memory_block_change_state(mem, MEM_ONLINE, MEM_OFFLINE);

        /* clear online_type */
        mem->online_type = -1;

        return ret;
}

static int memory_subsys_offline(struct device *dev)
{
        struct memory_block *mem = to_memory_block(dev);

        if (mem->state == MEM_OFFLINE)
                return 0;

        /* Can't offline block with non-present sections */
        if (mem->section_count != sections_per_block)
                return -EINVAL;

        return memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE);
}

static ssize_t state_store(struct device *dev, struct device_attribute *attr,
                           const char *buf, size_t count)
{
        struct memory_block *mem = to_memory_block(dev);
        int ret, online_type;

        ret = lock_device_hotplug_sysfs();
        if (ret)
                return ret;

        if (sysfs_streq(buf, "online_kernel"))
                online_type = MMOP_ONLINE_KERNEL;
        else if (sysfs_streq(buf, "online_movable"))
                online_type = MMOP_ONLINE_MOVABLE;
        else if (sysfs_streq(buf, "online"))
                online_type = MMOP_ONLINE_KEEP;
        else if (sysfs_streq(buf, "offline"))
                online_type = MMOP_OFFLINE;
        else {
                ret = -EINVAL;
                goto err;
        }

        switch (online_type) {
        case MMOP_ONLINE_KERNEL:
        case MMOP_ONLINE_MOVABLE:
        case MMOP_ONLINE_KEEP:
                /* mem->online_type is protected by device_hotplug_lock */
                mem->online_type = online_type;
                ret = device_online(&mem->dev);
                break;
        case MMOP_OFFLINE:
                ret = device_offline(&mem->dev);
                break;
        default:
                ret = -EINVAL; /* should never happen */
        }

err:
        unlock_device_hotplug();

        if (ret < 0)
                return ret;
        if (ret)
                return -EINVAL;

        return count;
}

/*
 * phys_device is a bad name for this.  What I really want
 * is a way to differentiate between memory ranges that
 * are part of physical devices that constitute
 * a complete removable unit or fru.
 * i.e. do these ranges belong to the same physical device,
 * s.t. if I offline all of these sections I can then
 * remove the physical device?
 */
static ssize_t phys_device_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct memory_block *mem = to_memory_block(dev);
        return sprintf(buf, "%d\n", mem->phys_device);
}

#ifdef CONFIG_MEMORY_HOTREMOVE
static void print_allowed_zone(char *buf, int nid, unsigned long start_pfn,
                unsigned long nr_pages, int online_type,
                struct zone *default_zone)
{
        struct zone *zone;

        zone = zone_for_pfn_range(online_type, nid, start_pfn, nr_pages);
        if (zone != default_zone) {
                strcat(buf, " ");
                strcat(buf, zone->name);
        }
}

static ssize_t valid_zones_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct memory_block *mem = to_memory_block(dev);
        unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
        unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
        unsigned long valid_start_pfn, valid_end_pfn;
        struct zone *default_zone;
        int nid;

        /*
         * Check the existing zone. Make sure that we do that only on the
         * online nodes otherwise the page_zone is not reliable
         */
        if (mem->state == MEM_ONLINE) {
                /*
                 * The block contains more than one zone can not be offlined.
                 * This can happen e.g. for ZONE_DMA and ZONE_DMA32
                 */
                if (!test_pages_in_a_zone(start_pfn, start_pfn + nr_pages,
                                          &valid_start_pfn, &valid_end_pfn))
                        return sprintf(buf, "none\n");
                start_pfn = valid_start_pfn;
                strcat(buf, page_zone(pfn_to_page(start_pfn))->name);
                goto out;
        }

        nid = mem->nid;
        default_zone = zone_for_pfn_range(MMOP_ONLINE_KEEP, nid, start_pfn, nr_pages);
        strcat(buf, default_zone->name);

        print_allowed_zone(buf, nid, start_pfn, nr_pages, MMOP_ONLINE_KERNEL,
                        default_zone);
        print_allowed_zone(buf, nid, start_pfn, nr_pages, MMOP_ONLINE_MOVABLE,
                        default_zone);
out:
        strcat(buf, "\n");

        return strlen(buf);
}
static DEVICE_ATTR_RO(valid_zones);
#endif

static DEVICE_ATTR_RO(phys_index);
static DEVICE_ATTR_RW(state);
static DEVICE_ATTR_RO(phys_device);
static DEVICE_ATTR_RO(removable);

/*
 * Show the memory block size (shared by all memory blocks).
 */
static ssize_t block_size_bytes_show(struct device *dev,
                                     struct device_attribute *attr, char *buf)
{
        return sprintf(buf, "%lx\n", memory_block_size_bytes());
}

static DEVICE_ATTR_RO(block_size_bytes);

/*
 * Memory auto online policy.
 */

static ssize_t auto_online_blocks_show(struct device *dev,
                                       struct device_attribute *attr, char *buf)
{
        if (memhp_auto_online)
                return sprintf(buf, "online\n");
        else
                return sprintf(buf, "offline\n");
}

static ssize_t auto_online_blocks_store(struct device *dev,
                                        struct device_attribute *attr,
                                        const char *buf, size_t count)
{
        if (sysfs_streq(buf, "online"))
                memhp_auto_online = true;
        else if (sysfs_streq(buf, "offline"))
                memhp_auto_online = false;
        else
                return -EINVAL;

        return count;
}

static DEVICE_ATTR_RW(auto_online_blocks);

/*
 * Some architectures will have custom drivers to do this, and
 * will not need to do it from userspace.  The fake hot-add code
 * as well as ppc64 will do all of their discovery in userspace
 * and will require this interface.
 */
#ifdef CONFIG_ARCH_MEMORY_PROBE
static ssize_t probe_store(struct device *dev, struct device_attribute *attr,
                           const char *buf, size_t count)
{
        u64 phys_addr;
        int nid, ret;
        unsigned long pages_per_block = PAGES_PER_SECTION * sections_per_block;

        ret = kstrtoull(buf, 0, &phys_addr);
        if (ret)
                return ret;

        if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
                return -EINVAL;

        ret = lock_device_hotplug_sysfs();
        if (ret)
                return ret;

        nid = memory_add_physaddr_to_nid(phys_addr);
        ret = __add_memory(nid, phys_addr,
                           MIN_MEMORY_BLOCK_SIZE * sections_per_block);

        if (ret)
                goto out;

        ret = count;
out:
        unlock_device_hotplug();
        return ret;
}

static DEVICE_ATTR_WO(probe);
#endif

#ifdef CONFIG_MEMORY_FAILURE
/*
 * Support for offlining pages of memory
 */

/* Soft offline a page */
static ssize_t soft_offline_page_store(struct device *dev,
                                       struct device_attribute *attr,
                                       const char *buf, size_t count)
{
        int ret;
        u64 pfn;
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
        if (kstrtoull(buf, 0, &pfn) < 0)
                return -EINVAL;
        pfn >>= PAGE_SHIFT;
        ret = soft_offline_page(pfn, 0);
        return ret == 0 ? count : ret;
}

/* Forcibly offline a page, including killing processes. */
static ssize_t hard_offline_page_store(struct device *dev,
                                       struct device_attribute *attr,
                                       const char *buf, size_t count)
{
        int ret;
        u64 pfn;
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
        if (kstrtoull(buf, 0, &pfn) < 0)
                return -EINVAL;
        pfn >>= PAGE_SHIFT;
        ret = memory_failure(pfn, 0);
        return ret ? ret : count;
}

static DEVICE_ATTR_WO(soft_offline_page);
static DEVICE_ATTR_WO(hard_offline_page);
#endif

/*
 * Note that phys_device is optional.  It is here to allow for
 * differentiation between which *physical* devices each
 * section belongs to...
 */
int __weak arch_get_memory_phys_device(unsigned long start_pfn)
{
        return 0;
}

/* A reference for the returned memory block device is acquired. */
static struct memory_block *find_memory_block_by_id(unsigned long block_id)
{
        struct device *dev;

        dev = subsys_find_device_by_id(&memory_subsys, block_id, NULL);
        return dev ? to_memory_block(dev) : NULL;
}

/*
 * For now, we have a linear search to go find the appropriate
 * memory_block corresponding to a particular phys_index. If
 * this gets to be a real problem, we can always use a radix
 * tree or something here.
 *
 * This could be made generic for all device subsystems.
 */
struct memory_block *find_memory_block(struct mem_section *section)
{
        unsigned long block_id = base_memory_block_id(__section_nr(section));

        return find_memory_block_by_id(block_id);
}

static struct attribute *memory_memblk_attrs[] = {
        &dev_attr_phys_index.attr,
        &dev_attr_state.attr,
        &dev_attr_phys_device.attr,
        &dev_attr_removable.attr,
#ifdef CONFIG_MEMORY_HOTREMOVE
        &dev_attr_valid_zones.attr,
#endif
        NULL
};

static struct attribute_group memory_memblk_attr_group = {
        .attrs = memory_memblk_attrs,
};

static const struct attribute_group *memory_memblk_attr_groups[] = {
        &memory_memblk_attr_group,
        NULL,
};

/*
 * register_memory - Setup a sysfs device for a memory block
 */
static
int register_memory(struct memory_block *memory)
{
        int ret;

        memory->dev.bus = &memory_subsys;
        memory->dev.id = memory->start_section_nr / sections_per_block;
        memory->dev.release = memory_block_release;
        memory->dev.groups = memory_memblk_attr_groups;
        memory->dev.offline = memory->state == MEM_OFFLINE;

        ret = device_register(&memory->dev);
        if (ret)
                put_device(&memory->dev);

        return ret;
}

static int init_memory_block(struct memory_block **memory,
                             unsigned long block_id, unsigned long state)
{
        struct memory_block *mem;
        unsigned long start_pfn;
        int ret = 0;

        mem = find_memory_block_by_id(block_id);
        if (mem) {
                put_device(&mem->dev);
                return -EEXIST;
        }
        mem = kzalloc(sizeof(*mem), GFP_KERNEL);
        if (!mem)
                return -ENOMEM;

        mem->start_section_nr = block_id * sections_per_block;
        mem->state = state;
        start_pfn = section_nr_to_pfn(mem->start_section_nr);
        mem->phys_device = arch_get_memory_phys_device(start_pfn);
        mem->nid = NUMA_NO_NODE;

        ret = register_memory(mem);

        *memory = mem;
        return ret;
}

static int add_memory_block(unsigned long base_section_nr)
{
        int ret, section_count = 0;
        struct memory_block *mem;
        unsigned long nr;

        for (nr = base_section_nr; nr < base_section_nr + sections_per_block;
             nr++)
                if (present_section_nr(nr))
                        section_count++;

        if (section_count == 0)
                return 0;
        ret = init_memory_block(&mem, base_memory_block_id(base_section_nr),
                                MEM_ONLINE);
        if (ret)
                return ret;
        mem->section_count = section_count;
        return 0;
}

static void unregister_memory(struct memory_block *memory)
{
        if (WARN_ON_ONCE(memory->dev.bus != &memory_subsys))
                return;

        /* drop the ref. we got via find_memory_block() */
        put_device(&memory->dev);
        device_unregister(&memory->dev);
}

/*
 * Create memory block devices for the given memory area. Start and size
 * have to be aligned to memory block granularity. Memory block devices
 * will be initialized as offline.
 *
 * Called under device_hotplug_lock.
 */
int create_memory_block_devices(unsigned long start, unsigned long size)
{
        const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start));
        unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
        struct memory_block *mem;
        unsigned long block_id;
        int ret = 0;

        if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) ||
                         !IS_ALIGNED(size, memory_block_size_bytes())))
                return -EINVAL;

        for (block_id = start_block_id; block_id != end_block_id; block_id++) {
                ret = init_memory_block(&mem, block_id, MEM_OFFLINE);
                if (ret)
                        break;
                mem->section_count = sections_per_block;
        }
        if (ret) {
                end_block_id = block_id;
                for (block_id = start_block_id; block_id != end_block_id;
                     block_id++) {
                        mem = find_memory_block_by_id(block_id);
                        if (WARN_ON_ONCE(!mem))
                                continue;
                        mem->section_count = 0;
                        unregister_memory(mem);
                }
        }
        return ret;
}

/*
 * Remove memory block devices for the given memory area. Start and size
 * have to be aligned to memory block granularity. Memory block devices
 * have to be offline.
 *
 * Called under device_hotplug_lock.
 */
void remove_memory_block_devices(unsigned long start, unsigned long size)
{
        const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start));
        const unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
        struct memory_block *mem;
        unsigned long block_id;

        if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) ||
                         !IS_ALIGNED(size, memory_block_size_bytes())))
                return;

        for (block_id = start_block_id; block_id != end_block_id; block_id++) {
                mem = find_memory_block_by_id(block_id);
                if (WARN_ON_ONCE(!mem))
                        continue;
                mem->section_count = 0;
                unregister_memory_block_under_nodes(mem);
                unregister_memory(mem);
        }
}

/* return true if the memory block is offlined, otherwise, return false */
bool is_memblock_offlined(struct memory_block *mem)
{
        return mem->state == MEM_OFFLINE;
}

static struct attribute *memory_root_attrs[] = {
#ifdef CONFIG_ARCH_MEMORY_PROBE
        &dev_attr_probe.attr,
#endif

#ifdef CONFIG_MEMORY_FAILURE
        &dev_attr_soft_offline_page.attr,
        &dev_attr_hard_offline_page.attr,
#endif

        &dev_attr_block_size_bytes.attr,
        &dev_attr_auto_online_blocks.attr,
        NULL
};

static struct attribute_group memory_root_attr_group = {
        .attrs = memory_root_attrs,
};

static const struct attribute_group *memory_root_attr_groups[] = {
        &memory_root_attr_group,
        NULL,
};

/*
 * Initialize the sysfs support for memory devices. At the time this function
 * is called, we cannot have concurrent creation/deletion of memory block
 * devices, the device_hotplug_lock is not needed.
 */
void __init memory_dev_init(void)
{
        int ret;
        unsigned long block_sz, nr;

        /* Validate the configured memory block size */
        block_sz = memory_block_size_bytes();
        if (!is_power_of_2(block_sz) || block_sz < MIN_MEMORY_BLOCK_SIZE)
                panic("Memory block size not suitable: 0x%lx\n", block_sz);
        sections_per_block = block_sz / MIN_MEMORY_BLOCK_SIZE;

        ret = subsys_system_register(&memory_subsys, memory_root_attr_groups);
        if (ret)
                panic("%s() failed to register subsystem: %d\n", __func__, ret);

        /*
         * Create entries for memory sections that were found
         * during boot and have been initialized
         */
        for (nr = 0; nr <= __highest_present_section_nr;
             nr += sections_per_block) {
                ret = add_memory_block(nr);
                if (ret)
                        panic("%s() failed to add memory block: %d\n", __func__,
                              ret);
        }
}

/**
 * walk_memory_blocks - walk through all present memory blocks overlapped
 *                      by the range [start, start + size)
 *
 * @start: start address of the memory range
 * @size: size of the memory range
 * @arg: argument passed to func
 * @func: callback for each memory section walked
 *
 * This function walks through all present memory blocks overlapped by the
 * range [start, start + size), calling func on each memory block.
 *
 * In case func() returns an error, walking is aborted and the error is
 * returned.
 */
int walk_memory_blocks(unsigned long start, unsigned long size,
                       void *arg, walk_memory_blocks_func_t func)
{
        const unsigned long start_block_id = phys_to_block_id(start);
        const unsigned long end_block_id = phys_to_block_id(start + size - 1);
        struct memory_block *mem;
        unsigned long block_id;
        int ret = 0;

        if (!size)
                return 0;

        for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
                mem = find_memory_block_by_id(block_id);
                if (!mem)
                        continue;

                ret = func(mem, arg);
                put_device(&mem->dev);
                if (ret)
                        break;
        }
        return ret;
}

struct for_each_memory_block_cb_data {
        walk_memory_blocks_func_t func;
        void *arg;
};

static int for_each_memory_block_cb(struct device *dev, void *data)
{
        struct memory_block *mem = to_memory_block(dev);
        struct for_each_memory_block_cb_data *cb_data = data;

        return cb_data->func(mem, cb_data->arg);
}

/**
 * for_each_memory_block - walk through all present memory blocks
 *
 * @arg: argument passed to func
 * @func: callback for each memory block walked
 *
 * This function walks through all present memory blocks, calling func on
 * each memory block.
 *
 * In case func() returns an error, walking is aborted and the error is
 * returned.
 */
int for_each_memory_block(void *arg, walk_memory_blocks_func_t func)
{
        struct for_each_memory_block_cb_data cb_data = {
                .func = func,
                .arg = arg,
        };

        return bus_for_each_dev(&memory_subsys, NULL, &cb_data,
                                for_each_memory_block_cb);
}