#ifndef _LINUX_MEMREMAP_H_
#define _LINUX_MEMREMAP_H_
#include <linux/mm.h>
#include <linux/ioport.h>
#include <linux/percpu-refcount.h>

struct resource;
struct device;

/**
 * struct vmem_altmap - pre-allocated storage for vmemmap_populate
 * @base_pfn: base of the entire dev_pagemap mapping
 * @reserve: pages mapped, but reserved for driver use (relative to @base)
 * @free: free pages set aside in the mapping for memmap storage
 * @align: pages reserved to meet allocation alignments
 * @alloc: track pages consumed, private to vmemmap_populate()
 */
struct vmem_altmap {
        const unsigned long base_pfn;
        const unsigned long reserve;
        unsigned long free;
        unsigned long align;
        unsigned long alloc;
};

unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns);

#if defined(CONFIG_SPARSEMEM_VMEMMAP) && defined(CONFIG_ZONE_DEVICE)
struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start);
#else
static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
{
        return NULL;
}
#endif

/*
 * Specialize ZONE_DEVICE memory into multiple types each having differents
 * usage.
 *
 * MEMORY_DEVICE_PUBLIC:
 * Persistent device memory (pmem): struct page might be allocated in different
 * memory and architecture might want to perform special actions. It is similar
 * to regular memory, in that the CPU can access it transparently. However,
 * it is likely to have different bandwidth and latency than regular memory.
 * See Documentation/nvdimm/nvdimm.txt for more information.
 *
 * MEMORY_HMM:
 * Device memory that is not directly addressable by the CPU: CPU can neither
 * read nor write _UNADDRESSABLE memory. In this case, we do still have struct
 * pages backing the device memory. Doing so simplifies the implementation, but
 * it is important to remember that there are certain points at which the struct
 * page must be treated as an opaque object, rather than a "normal" struct page.
 * A more complete discussion of unaddressable memory may be found in
 * include/linux/hmm.h and Documentation/vm/hmm.txt.
 */
enum memory_type {
        MEMORY_DEVICE_PUBLIC = 0,
        MEMORY_HMM,
};

/*
 * For MEMORY_HMM we use ZONE_DEVICE and extend it with two callbacks:
 *   page_fault()
 *   page_free()
 *
 * Additional notes about MEMORY_DEVICE_PRIVATE may be found in
 * include/linux/hmm.h and Documentation/vm/hmm.txt. There is also a brief
 * explanation in include/linux/memory_hotplug.h.
 *
 * The page_fault() callback must migrate page back, from device memory to
 * system memory, so that the CPU can access it. This might fail for various
 * reasons (device issues,  device have been unplugged, ...). When such error
 * conditions happen, the page_fault() callback must return VM_FAULT_SIGBUS and
 * set the CPU page table entry to "poisoned".
 *
 * Note that because memory cgroup charges are transferred to the device memory,
 * this should never fail due to memory restrictions. However, allocation
 * of a regular system page might still fail because we are out of memory. If
 * that happens, the page_fault() callback must return VM_FAULT_OOM.
 *
 * The page_fault() callback can also try to migrate back multiple pages in one
 * chunk, as an optimization. It must, however, prioritize the faulting address
 * over all the others.
 *
 *
 * The page_free() callback is called once the page refcount reaches 1
 * (ZONE_DEVICE pages never reach 0 refcount unless there is a refcount bug.
 * This allows the device driver to implement its own memory management.)
 */
typedef int (*dev_page_fault_t)(struct vm_area_struct *vma,
                                unsigned long addr,
                                struct page *page,
                                unsigned int flags,
                                pmd_t *pmdp);
typedef void (*dev_page_free_t)(struct page *page, void *data);

/**
 * struct dev_pagemap - metadata for ZONE_DEVICE mappings
 * @altmap: pre-allocated/reserved memory for vmemmap allocations
 * @page_fault: callback when CPU fault on an un-addressable device page
 * @page_free: free page callback when page refcount reach 1
 * @res: physical address range covered by @ref
 * @ref: reference count that pins the devm_memremap_pages() mapping
 * @dev: host device of the mapping for debug
 * @data: privata data pointer for page_free
 * @type: memory type: see MEMORY_* above
 */
struct dev_pagemap {
        struct vmem_altmap *altmap;
        dev_page_fault_t page_fault;
        dev_page_free_t page_free;
        const struct resource *res;
        struct percpu_ref *ref;
        struct device *dev;
        void *data;
        enum memory_type type;
};

#ifdef CONFIG_ZONE_DEVICE
void *devm_memremap_pages(struct device *dev, struct resource *res,
                struct percpu_ref *ref, struct vmem_altmap *altmap);
struct dev_pagemap *find_dev_pagemap(resource_size_t phys);

static inline bool is_hmm_page(const struct page *page)
{
        /* See MEMORY_DEVICE_PRIVATE in include/linux/memory_hotplug.h */
        return ((page_zonenum(page) == ZONE_DEVICE) &&
                (page->pgmap->type == MEMORY_HMM));
}
#else
static inline void *devm_memremap_pages(struct device *dev,
                struct resource *res, struct percpu_ref *ref,
                struct vmem_altmap *altmap)
{
        /*
         * Fail attempts to call devm_memremap_pages() without
         * ZONE_DEVICE support enabled, this requires callers to fall
         * back to plain devm_memremap() based on config
         */
        WARN_ON_ONCE(1);
        return ERR_PTR(-ENXIO);
}

static inline struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
{
        return NULL;
}

static inline bool is_hmm_page(const struct page *page)
{
        return false;
}
#endif

/**
 * get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn
 * @pfn: page frame number to lookup page_map
 * @pgmap: optional known pgmap that already has a reference
 *
 * @pgmap allows the overhead of a lookup to be bypassed when @pfn lands in the
 * same mapping.
 */
static inline struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
                struct dev_pagemap *pgmap)
{
        const struct resource *res = pgmap ? pgmap->res : NULL;
        resource_size_t phys = PFN_PHYS(pfn);

        /*
         * In the cached case we're already holding a live reference so
         * we can simply do a blind increment
         */
        if (res && phys >= res->start && phys <= res->end) {
                percpu_ref_get(pgmap->ref);
                return pgmap;
        }

        /* fall back to slow path lookup */
        rcu_read_lock();
        pgmap = find_dev_pagemap(phys);
        if (pgmap && !percpu_ref_tryget_live(pgmap->ref))
                pgmap = NULL;
        rcu_read_unlock();

        return pgmap;
}

static inline void put_dev_pagemap(struct dev_pagemap *pgmap)
{
        if (pgmap) {
                WARN_ON(percpu_ref_is_zero(pgmap->ref));
                percpu_ref_put(pgmap->ref);
        }
}
#endif /* _LINUX_MEMREMAP_H_ */