xref: /linux/kernel/dma/swiotlb.c (revision 1553a1c48281243359a9529a10ddb551f3b967ab)

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Dynamic DMA mapping support.
 *
 * This implementation is a fallback for platforms that do not support
 * I/O TLBs (aka DMA address translation hardware).
 * Copyright (C) 2000 Asit Mallick <Asit.K.Mallick@intel.com>
 * Copyright (C) 2000 Goutham Rao <goutham.rao@intel.com>
 * Copyright (C) 2000, 2003 Hewlett-Packard Co
 *	David Mosberger-Tang <davidm@hpl.hp.com>
 *
 * 03/05/07 davidm	Switch from PCI-DMA to generic device DMA API.
 * 00/12/13 davidm	Rename to swiotlb.c and add mark_clean() to avoid
 *			unnecessary i-cache flushing.
 * 04/07/.. ak		Better overflow handling. Assorted fixes.
 * 05/09/10 linville	Add support for syncing ranges, support syncing for
 *			DMA_BIDIRECTIONAL mappings, miscellaneous cleanup.
 * 08/12/11 beckyb	Add highmem support
 */

#define pr_fmt(fmt) "software IO TLB: " fmt

#include <linux/cache.h>
#include <linux/cc_platform.h>
#include <linux/ctype.h>
#include <linux/debugfs.h>
#include <linux/dma-direct.h>
#include <linux/dma-map-ops.h>
#include <linux/export.h>
#include <linux/gfp.h>
#include <linux/highmem.h>
#include <linux/io.h>
#include <linux/iommu-helper.h>
#include <linux/init.h>
#include <linux/memblock.h>
#include <linux/mm.h>
#include <linux/pfn.h>
#include <linux/rculist.h>
#include <linux/scatterlist.h>
#include <linux/set_memory.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/swiotlb.h>
#include <linux/types.h>
#ifdef CONFIG_DMA_RESTRICTED_POOL
#include <linux/of.h>
#include <linux/of_fdt.h>
#include <linux/of_reserved_mem.h>
#include <linux/slab.h>
#endif

#define CREATE_TRACE_POINTS
#include <trace/events/swiotlb.h>

#define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))

/*
 * Minimum IO TLB size to bother booting with.  Systems with mainly
 * 64bit capable cards will only lightly use the swiotlb.  If we can't
 * allocate a contiguous 1MB, we're probably in trouble anyway.
 */
#define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)

#define INVALID_PHYS_ADDR (~(phys_addr_t)0)

/**
 * struct io_tlb_slot - IO TLB slot descriptor
 * @orig_addr:	The original address corresponding to a mapped entry.
 * @alloc_size:	Size of the allocated buffer.
 * @list:	The free list describing the number of free entries available
 *		from each index.
 */
struct io_tlb_slot {
	phys_addr_t orig_addr;
	size_t alloc_size;
	unsigned int list;
};

static bool swiotlb_force_bounce;
static bool swiotlb_force_disable;

#ifdef CONFIG_SWIOTLB_DYNAMIC

static void swiotlb_dyn_alloc(struct work_struct *work);

static struct io_tlb_mem io_tlb_default_mem = {
	.lock = __SPIN_LOCK_UNLOCKED(io_tlb_default_mem.lock),
	.pools = LIST_HEAD_INIT(io_tlb_default_mem.pools),
	.dyn_alloc = __WORK_INITIALIZER(io_tlb_default_mem.dyn_alloc,
					swiotlb_dyn_alloc),
};

#else  /* !CONFIG_SWIOTLB_DYNAMIC */

static struct io_tlb_mem io_tlb_default_mem;

#endif	/* CONFIG_SWIOTLB_DYNAMIC */

static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
static unsigned long default_nareas;

/**
 * struct io_tlb_area - IO TLB memory area descriptor
 *
 * This is a single area with a single lock.
 *
 * @used:	The number of used IO TLB block.
 * @index:	The slot index to start searching in this area for next round.
 * @lock:	The lock to protect the above data structures in the map and
 *		unmap calls.
 */
struct io_tlb_area {
	unsigned long used;
	unsigned int index;
	spinlock_t lock;
};

/*
 * Round up number of slabs to the next power of 2. The last area is going
 * be smaller than the rest if default_nslabs is not power of two.
 * The number of slot in an area should be a multiple of IO_TLB_SEGSIZE,
 * otherwise a segment may span two or more areas. It conflicts with free
 * contiguous slots tracking: free slots are treated contiguous no matter
 * whether they cross an area boundary.
 *
 * Return true if default_nslabs is rounded up.
 */
static bool round_up_default_nslabs(void)
{
	if (!default_nareas)
		return false;

	if (default_nslabs < IO_TLB_SEGSIZE * default_nareas)
		default_nslabs = IO_TLB_SEGSIZE * default_nareas;
	else if (is_power_of_2(default_nslabs))
		return false;
	default_nslabs = roundup_pow_of_two(default_nslabs);
	return true;
}

/**
 * swiotlb_adjust_nareas() - adjust the number of areas and slots
 * @nareas:	Desired number of areas. Zero is treated as 1.
 *
 * Adjust the default number of areas in a memory pool.
 * The default size of the memory pool may also change to meet minimum area
 * size requirements.
 */
static void swiotlb_adjust_nareas(unsigned int nareas)
{
	if (!nareas)
		nareas = 1;
	else if (!is_power_of_2(nareas))
		nareas = roundup_pow_of_two(nareas);

	default_nareas = nareas;

	pr_info("area num %d.\n", nareas);
	if (round_up_default_nslabs())
		pr_info("SWIOTLB bounce buffer size roundup to %luMB",
			(default_nslabs << IO_TLB_SHIFT) >> 20);
}

/**
 * limit_nareas() - get the maximum number of areas for a given memory pool size
 * @nareas:	Desired number of areas.
 * @nslots:	Total number of slots in the memory pool.
 *
 * Limit the number of areas to the maximum possible number of areas in
 * a memory pool of the given size.
 *
 * Return: Maximum possible number of areas.
 */
static unsigned int limit_nareas(unsigned int nareas, unsigned long nslots)
{
	if (nslots < nareas * IO_TLB_SEGSIZE)
		return nslots / IO_TLB_SEGSIZE;
	return nareas;
}

static int __init
setup_io_tlb_npages(char *str)
{
	if (isdigit(*str)) {
		/* avoid tail segment of size < IO_TLB_SEGSIZE */
		default_nslabs =
			ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE);
	}
	if (*str == ',')
		++str;
	if (isdigit(*str))
		swiotlb_adjust_nareas(simple_strtoul(str, &str, 0));
	if (*str == ',')
		++str;
	if (!strcmp(str, "force"))
		swiotlb_force_bounce = true;
	else if (!strcmp(str, "noforce"))
		swiotlb_force_disable = true;

	return 0;
}
early_param("swiotlb", setup_io_tlb_npages);

unsigned long swiotlb_size_or_default(void)
{
	return default_nslabs << IO_TLB_SHIFT;
}

void __init swiotlb_adjust_size(unsigned long size)
{
	/*
	 * If swiotlb parameter has not been specified, give a chance to
	 * architectures such as those supporting memory encryption to
	 * adjust/expand SWIOTLB size for their use.
	 */
	if (default_nslabs != IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT)
		return;

	size = ALIGN(size, IO_TLB_SIZE);
	default_nslabs = ALIGN(size >> IO_TLB_SHIFT, IO_TLB_SEGSIZE);
	if (round_up_default_nslabs())
		size = default_nslabs << IO_TLB_SHIFT;
	pr_info("SWIOTLB bounce buffer size adjusted to %luMB", size >> 20);
}

void swiotlb_print_info(void)
{
	struct io_tlb_pool *mem = &io_tlb_default_mem.defpool;

	if (!mem->nslabs) {
		pr_warn("No low mem\n");
		return;
	}

	pr_info("mapped [mem %pa-%pa] (%luMB)\n", &mem->start, &mem->end,
	       (mem->nslabs << IO_TLB_SHIFT) >> 20);
}

static inline unsigned long io_tlb_offset(unsigned long val)
{
	return val & (IO_TLB_SEGSIZE - 1);
}

static inline unsigned long nr_slots(u64 val)
{
	return DIV_ROUND_UP(val, IO_TLB_SIZE);
}

/*
 * Early SWIOTLB allocation may be too early to allow an architecture to
 * perform the desired operations.  This function allows the architecture to
 * call SWIOTLB when the operations are possible.  It needs to be called
 * before the SWIOTLB memory is used.
 */
void __init swiotlb_update_mem_attributes(void)
{
	struct io_tlb_pool *mem = &io_tlb_default_mem.defpool;
	unsigned long bytes;

	if (!mem->nslabs || mem->late_alloc)
		return;
	bytes = PAGE_ALIGN(mem->nslabs << IO_TLB_SHIFT);
	set_memory_decrypted((unsigned long)mem->vaddr, bytes >> PAGE_SHIFT);
}

static void swiotlb_init_io_tlb_pool(struct io_tlb_pool *mem, phys_addr_t start,
		unsigned long nslabs, bool late_alloc, unsigned int nareas)
{
	void *vaddr = phys_to_virt(start);
	unsigned long bytes = nslabs << IO_TLB_SHIFT, i;

	mem->nslabs = nslabs;
	mem->start = start;
	mem->end = mem->start + bytes;
	mem->late_alloc = late_alloc;
	mem->nareas = nareas;
	mem->area_nslabs = nslabs / mem->nareas;

	for (i = 0; i < mem->nareas; i++) {
		spin_lock_init(&mem->areas[i].lock);
		mem->areas[i].index = 0;
		mem->areas[i].used = 0;
	}

	for (i = 0; i < mem->nslabs; i++) {
		mem->slots[i].list = min(IO_TLB_SEGSIZE - io_tlb_offset(i),
					 mem->nslabs - i);
		mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
		mem->slots[i].alloc_size = 0;
	}

	memset(vaddr, 0, bytes);
	mem->vaddr = vaddr;
	return;
}

/**
 * add_mem_pool() - add a memory pool to the allocator
 * @mem:	Software IO TLB allocator.
 * @pool:	Memory pool to be added.
 */
static void add_mem_pool(struct io_tlb_mem *mem, struct io_tlb_pool *pool)
{
#ifdef CONFIG_SWIOTLB_DYNAMIC
	spin_lock(&mem->lock);
	list_add_rcu(&pool->node, &mem->pools);
	mem->nslabs += pool->nslabs;
	spin_unlock(&mem->lock);
#else
	mem->nslabs = pool->nslabs;
#endif
}

static void __init *swiotlb_memblock_alloc(unsigned long nslabs,
		unsigned int flags,
		int (*remap)(void *tlb, unsigned long nslabs))
{
	size_t bytes = PAGE_ALIGN(nslabs << IO_TLB_SHIFT);
	void *tlb;

	/*
	 * By default allocate the bounce buffer memory from low memory, but
	 * allow to pick a location everywhere for hypervisors with guest
	 * memory encryption.
	 */
	if (flags & SWIOTLB_ANY)
		tlb = memblock_alloc(bytes, PAGE_SIZE);
	else
		tlb = memblock_alloc_low(bytes, PAGE_SIZE);

	if (!tlb) {
		pr_warn("%s: Failed to allocate %zu bytes tlb structure\n",
			__func__, bytes);
		return NULL;
	}

	if (remap && remap(tlb, nslabs) < 0) {
		memblock_free(tlb, PAGE_ALIGN(bytes));
		pr_warn("%s: Failed to remap %zu bytes\n", __func__, bytes);
		return NULL;
	}

	return tlb;
}

/*
 * Statically reserve bounce buffer space and initialize bounce buffer data
 * structures for the software IO TLB used to implement the DMA API.
 */
void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
		int (*remap)(void *tlb, unsigned long nslabs))
{
	struct io_tlb_pool *mem = &io_tlb_default_mem.defpool;
	unsigned long nslabs;
	unsigned int nareas;
	size_t alloc_size;
	void *tlb;

	if (!addressing_limit && !swiotlb_force_bounce)
		return;
	if (swiotlb_force_disable)
		return;

	io_tlb_default_mem.force_bounce =
		swiotlb_force_bounce || (flags & SWIOTLB_FORCE);

#ifdef CONFIG_SWIOTLB_DYNAMIC
	if (!remap)
		io_tlb_default_mem.can_grow = true;
	if (flags & SWIOTLB_ANY)
		io_tlb_default_mem.phys_limit = virt_to_phys(high_memory - 1);
	else
		io_tlb_default_mem.phys_limit = ARCH_LOW_ADDRESS_LIMIT;
#endif

	if (!default_nareas)
		swiotlb_adjust_nareas(num_possible_cpus());

	nslabs = default_nslabs;
	nareas = limit_nareas(default_nareas, nslabs);
	while ((tlb = swiotlb_memblock_alloc(nslabs, flags, remap)) == NULL) {
		if (nslabs <= IO_TLB_MIN_SLABS)
			return;
		nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
		nareas = limit_nareas(nareas, nslabs);
	}

	if (default_nslabs != nslabs) {
		pr_info("SWIOTLB bounce buffer size adjusted %lu -> %lu slabs",
			default_nslabs, nslabs);
		default_nslabs = nslabs;
	}

	alloc_size = PAGE_ALIGN(array_size(sizeof(*mem->slots), nslabs));
	mem->slots = memblock_alloc(alloc_size, PAGE_SIZE);
	if (!mem->slots) {
		pr_warn("%s: Failed to allocate %zu bytes align=0x%lx\n",
			__func__, alloc_size, PAGE_SIZE);
		return;
	}

	mem->areas = memblock_alloc(array_size(sizeof(struct io_tlb_area),
		nareas), SMP_CACHE_BYTES);
	if (!mem->areas) {
		pr_warn("%s: Failed to allocate mem->areas.\n", __func__);
		return;
	}

	swiotlb_init_io_tlb_pool(mem, __pa(tlb), nslabs, false, nareas);
	add_mem_pool(&io_tlb_default_mem, mem);

	if (flags & SWIOTLB_VERBOSE)
		swiotlb_print_info();
}

void __init swiotlb_init(bool addressing_limit, unsigned int flags)
{
	swiotlb_init_remap(addressing_limit, flags, NULL);
}

/*
 * Systems with larger DMA zones (those that don't support ISA) can
 * initialize the swiotlb later using the slab allocator if needed.
 * This should be just like above, but with some error catching.
 */
int swiotlb_init_late(size_t size, gfp_t gfp_mask,
		int (*remap)(void *tlb, unsigned long nslabs))
{
	struct io_tlb_pool *mem = &io_tlb_default_mem.defpool;
	unsigned long nslabs = ALIGN(size >> IO_TLB_SHIFT, IO_TLB_SEGSIZE);
	unsigned int nareas;
	unsigned char *vstart = NULL;
	unsigned int order, area_order;
	bool retried = false;
	int rc = 0;

	if (io_tlb_default_mem.nslabs)
		return 0;

	if (swiotlb_force_disable)
		return 0;

	io_tlb_default_mem.force_bounce = swiotlb_force_bounce;

#ifdef CONFIG_SWIOTLB_DYNAMIC
	if (!remap)
		io_tlb_default_mem.can_grow = true;
	if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp_mask & __GFP_DMA))
		io_tlb_default_mem.phys_limit = DMA_BIT_MASK(zone_dma_bits);
	else if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp_mask & __GFP_DMA32))
		io_tlb_default_mem.phys_limit = DMA_BIT_MASK(32);
	else
		io_tlb_default_mem.phys_limit = virt_to_phys(high_memory - 1);
#endif

	if (!default_nareas)
		swiotlb_adjust_nareas(num_possible_cpus());

retry:
	order = get_order(nslabs << IO_TLB_SHIFT);
	nslabs = SLABS_PER_PAGE << order;

	while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
		vstart = (void *)__get_free_pages(gfp_mask | __GFP_NOWARN,
						  order);
		if (vstart)
			break;
		order--;
		nslabs = SLABS_PER_PAGE << order;
		retried = true;
	}

	if (!vstart)
		return -ENOMEM;

	if (remap)
		rc = remap(vstart, nslabs);
	if (rc) {
		free_pages((unsigned long)vstart, order);

		nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
		if (nslabs < IO_TLB_MIN_SLABS)
			return rc;
		retried = true;
		goto retry;
	}

	if (retried) {
		pr_warn("only able to allocate %ld MB\n",
			(PAGE_SIZE << order) >> 20);
	}

	nareas = limit_nareas(default_nareas, nslabs);
	area_order = get_order(array_size(sizeof(*mem->areas), nareas));
	mem->areas = (struct io_tlb_area *)
		__get_free_pages(GFP_KERNEL | __GFP_ZERO, area_order);
	if (!mem->areas)
		goto error_area;

	mem->slots = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
		get_order(array_size(sizeof(*mem->slots), nslabs)));
	if (!mem->slots)
		goto error_slots;

	set_memory_decrypted((unsigned long)vstart,
			     (nslabs << IO_TLB_SHIFT) >> PAGE_SHIFT);
	swiotlb_init_io_tlb_pool(mem, virt_to_phys(vstart), nslabs, true,
				 nareas);
	add_mem_pool(&io_tlb_default_mem, mem);

	swiotlb_print_info();
	return 0;

error_slots:
	free_pages((unsigned long)mem->areas, area_order);
error_area:
	free_pages((unsigned long)vstart, order);
	return -ENOMEM;
}

void __init swiotlb_exit(void)
{
	struct io_tlb_pool *mem = &io_tlb_default_mem.defpool;
	unsigned long tbl_vaddr;
	size_t tbl_size, slots_size;
	unsigned int area_order;

	if (swiotlb_force_bounce)
		return;

	if (!mem->nslabs)
		return;

	pr_info("tearing down default memory pool\n");
	tbl_vaddr = (unsigned long)phys_to_virt(mem->start);
	tbl_size = PAGE_ALIGN(mem->end - mem->start);
	slots_size = PAGE_ALIGN(array_size(sizeof(*mem->slots), mem->nslabs));

	set_memory_encrypted(tbl_vaddr, tbl_size >> PAGE_SHIFT);
	if (mem->late_alloc) {
		area_order = get_order(array_size(sizeof(*mem->areas),
			mem->nareas));
		free_pages((unsigned long)mem->areas, area_order);
		free_pages(tbl_vaddr, get_order(tbl_size));
		free_pages((unsigned long)mem->slots, get_order(slots_size));
	} else {
		memblock_free_late(__pa(mem->areas),
			array_size(sizeof(*mem->areas), mem->nareas));
		memblock_free_late(mem->start, tbl_size);
		memblock_free_late(__pa(mem->slots), slots_size);
	}

	memset(mem, 0, sizeof(*mem));
}

#ifdef CONFIG_SWIOTLB_DYNAMIC

/**
 * alloc_dma_pages() - allocate pages to be used for DMA
 * @gfp:	GFP flags for the allocation.
 * @bytes:	Size of the buffer.
 * @phys_limit:	Maximum allowed physical address of the buffer.
 *
 * Allocate pages from the buddy allocator. If successful, make the allocated
 * pages decrypted that they can be used for DMA.
 *
 * Return: Decrypted pages, %NULL on allocation failure, or ERR_PTR(-EAGAIN)
 * if the allocated physical address was above @phys_limit.
 */
static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
{
	unsigned int order = get_order(bytes);
	struct page *page;
	phys_addr_t paddr;
	void *vaddr;

	page = alloc_pages(gfp, order);
	if (!page)
		return NULL;

	paddr = page_to_phys(page);
	if (paddr + bytes - 1 > phys_limit) {
		__free_pages(page, order);
		return ERR_PTR(-EAGAIN);
	}

	vaddr = phys_to_virt(paddr);
	if (set_memory_decrypted((unsigned long)vaddr, PFN_UP(bytes)))
		goto error;
	return page;

error:
	/* Intentional leak if pages cannot be encrypted again. */
	if (!set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
		__free_pages(page, order);
	return NULL;
}

/**
 * swiotlb_alloc_tlb() - allocate a dynamic IO TLB buffer
 * @dev:	Device for which a memory pool is allocated.
 * @bytes:	Size of the buffer.
 * @phys_limit:	Maximum allowed physical address of the buffer.
 * @gfp:	GFP flags for the allocation.
 *
 * Return: Allocated pages, or %NULL on allocation failure.
 */
static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
		u64 phys_limit, gfp_t gfp)
{
	struct page *page;

	/*
	 * Allocate from the atomic pools if memory is encrypted and
	 * the allocation is atomic, because decrypting may block.
	 */
	if (!gfpflags_allow_blocking(gfp) && dev && force_dma_unencrypted(dev)) {
		void *vaddr;

		if (!IS_ENABLED(CONFIG_DMA_COHERENT_POOL))
			return NULL;

		return dma_alloc_from_pool(dev, bytes, &vaddr, gfp,
					   dma_coherent_ok);
	}

	gfp &= ~GFP_ZONEMASK;
	if (phys_limit <= DMA_BIT_MASK(zone_dma_bits))
		gfp |= __GFP_DMA;
	else if (phys_limit <= DMA_BIT_MASK(32))
		gfp |= __GFP_DMA32;

	while (IS_ERR(page = alloc_dma_pages(gfp, bytes, phys_limit))) {
		if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
		    phys_limit < DMA_BIT_MASK(64) &&
		    !(gfp & (__GFP_DMA32 | __GFP_DMA)))
			gfp |= __GFP_DMA32;
		else if (IS_ENABLED(CONFIG_ZONE_DMA) &&
			 !(gfp & __GFP_DMA))
			gfp = (gfp & ~__GFP_DMA32) | __GFP_DMA;
		else
			return NULL;
	}

	return page;
}

/**
 * swiotlb_free_tlb() - free a dynamically allocated IO TLB buffer
 * @vaddr:	Virtual address of the buffer.
 * @bytes:	Size of the buffer.
 */
static void swiotlb_free_tlb(void *vaddr, size_t bytes)
{
	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
	    dma_free_from_pool(NULL, vaddr, bytes))
		return;

	/* Intentional leak if pages cannot be encrypted again. */
	if (!set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
		__free_pages(virt_to_page(vaddr), get_order(bytes));
}

/**
 * swiotlb_alloc_pool() - allocate a new IO TLB memory pool
 * @dev:	Device for which a memory pool is allocated.
 * @minslabs:	Minimum number of slabs.
 * @nslabs:	Desired (maximum) number of slabs.
 * @nareas:	Number of areas.
 * @phys_limit:	Maximum DMA buffer physical address.
 * @gfp:	GFP flags for the allocations.
 *
 * Allocate and initialize a new IO TLB memory pool. The actual number of
 * slabs may be reduced if allocation of @nslabs fails. If even
 * @minslabs cannot be allocated, this function fails.
 *
 * Return: New memory pool, or %NULL on allocation failure.
 */
static struct io_tlb_pool *swiotlb_alloc_pool(struct device *dev,
		unsigned long minslabs, unsigned long nslabs,
		unsigned int nareas, u64 phys_limit, gfp_t gfp)
{
	struct io_tlb_pool *pool;
	unsigned int slot_order;
	struct page *tlb;
	size_t pool_size;
	size_t tlb_size;

	if (nslabs > SLABS_PER_PAGE << MAX_PAGE_ORDER) {
		nslabs = SLABS_PER_PAGE << MAX_PAGE_ORDER;
		nareas = limit_nareas(nareas, nslabs);
	}

	pool_size = sizeof(*pool) + array_size(sizeof(*pool->areas), nareas);
	pool = kzalloc(pool_size, gfp);
	if (!pool)
		goto error;
	pool->areas = (void *)pool + sizeof(*pool);

	tlb_size = nslabs << IO_TLB_SHIFT;
	while (!(tlb = swiotlb_alloc_tlb(dev, tlb_size, phys_limit, gfp))) {
		if (nslabs <= minslabs)
			goto error_tlb;
		nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
		nareas = limit_nareas(nareas, nslabs);
		tlb_size = nslabs << IO_TLB_SHIFT;
	}

	slot_order = get_order(array_size(sizeof(*pool->slots), nslabs));
	pool->slots = (struct io_tlb_slot *)
		__get_free_pages(gfp, slot_order);
	if (!pool->slots)
		goto error_slots;

	swiotlb_init_io_tlb_pool(pool, page_to_phys(tlb), nslabs, true, nareas);
	return pool;

error_slots:
	swiotlb_free_tlb(page_address(tlb), tlb_size);
error_tlb:
	kfree(pool);
error:
	return NULL;
}

/**
 * swiotlb_dyn_alloc() - dynamic memory pool allocation worker
 * @work:	Pointer to dyn_alloc in struct io_tlb_mem.
 */
static void swiotlb_dyn_alloc(struct work_struct *work)
{
	struct io_tlb_mem *mem =
		container_of(work, struct io_tlb_mem, dyn_alloc);
	struct io_tlb_pool *pool;

	pool = swiotlb_alloc_pool(NULL, IO_TLB_MIN_SLABS, default_nslabs,
				  default_nareas, mem->phys_limit, GFP_KERNEL);
	if (!pool) {
		pr_warn_ratelimited("Failed to allocate new pool");
		return;
	}

	add_mem_pool(mem, pool);
}

/**
 * swiotlb_dyn_free() - RCU callback to free a memory pool
 * @rcu:	RCU head in the corresponding struct io_tlb_pool.
 */
static void swiotlb_dyn_free(struct rcu_head *rcu)
{
	struct io_tlb_pool *pool = container_of(rcu, struct io_tlb_pool, rcu);
	size_t slots_size = array_size(sizeof(*pool->slots), pool->nslabs);
	size_t tlb_size = pool->end - pool->start;

	free_pages((unsigned long)pool->slots, get_order(slots_size));
	swiotlb_free_tlb(pool->vaddr, tlb_size);
	kfree(pool);
}

/**
 * swiotlb_find_pool() - find the IO TLB pool for a physical address
 * @dev:        Device which has mapped the DMA buffer.
 * @paddr:      Physical address within the DMA buffer.
 *
 * Find the IO TLB memory pool descriptor which contains the given physical
 * address, if any.
 *
 * Return: Memory pool which contains @paddr, or %NULL if none.
 */
struct io_tlb_pool *swiotlb_find_pool(struct device *dev, phys_addr_t paddr)
{
	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
	struct io_tlb_pool *pool;

	rcu_read_lock();
	list_for_each_entry_rcu(pool, &mem->pools, node) {
		if (paddr >= pool->start && paddr < pool->end)
			goto out;
	}

	list_for_each_entry_rcu(pool, &dev->dma_io_tlb_pools, node) {
		if (paddr >= pool->start && paddr < pool->end)
			goto out;
	}
	pool = NULL;
out:
	rcu_read_unlock();
	return pool;
}

/**
 * swiotlb_del_pool() - remove an IO TLB pool from a device
 * @dev:	Owning device.
 * @pool:	Memory pool to be removed.
 */
static void swiotlb_del_pool(struct device *dev, struct io_tlb_pool *pool)
{
	unsigned long flags;

	spin_lock_irqsave(&dev->dma_io_tlb_lock, flags);
	list_del_rcu(&pool->node);
	spin_unlock_irqrestore(&dev->dma_io_tlb_lock, flags);

	call_rcu(&pool->rcu, swiotlb_dyn_free);
}

#endif	/* CONFIG_SWIOTLB_DYNAMIC */

/**
 * swiotlb_dev_init() - initialize swiotlb fields in &struct device
 * @dev:	Device to be initialized.
 */
void swiotlb_dev_init(struct device *dev)
{
	dev->dma_io_tlb_mem = &io_tlb_default_mem;
#ifdef CONFIG_SWIOTLB_DYNAMIC
	INIT_LIST_HEAD(&dev->dma_io_tlb_pools);
	spin_lock_init(&dev->dma_io_tlb_lock);
	dev->dma_uses_io_tlb = false;
#endif
}

/*
 * Return the offset into a iotlb slot required to keep the device happy.
 */
static unsigned int swiotlb_align_offset(struct device *dev, u64 addr)
{
	return addr & dma_get_min_align_mask(dev) & (IO_TLB_SIZE - 1);
}

/*
 * Bounce: copy the swiotlb buffer from or back to the original dma location
 */
static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size,
			   enum dma_data_direction dir)
{
	struct io_tlb_pool *mem = swiotlb_find_pool(dev, tlb_addr);
	int index = (tlb_addr - mem->start) >> IO_TLB_SHIFT;
	phys_addr_t orig_addr = mem->slots[index].orig_addr;
	size_t alloc_size = mem->slots[index].alloc_size;
	unsigned long pfn = PFN_DOWN(orig_addr);
	unsigned char *vaddr = mem->vaddr + tlb_addr - mem->start;
	unsigned int tlb_offset, orig_addr_offset;

	if (orig_addr == INVALID_PHYS_ADDR)
		return;

	tlb_offset = tlb_addr & (IO_TLB_SIZE - 1);
	orig_addr_offset = swiotlb_align_offset(dev, orig_addr);
	if (tlb_offset < orig_addr_offset) {
		dev_WARN_ONCE(dev, 1,
			"Access before mapping start detected. orig offset %u, requested offset %u.\n",
			orig_addr_offset, tlb_offset);
		return;
	}

	tlb_offset -= orig_addr_offset;
	if (tlb_offset > alloc_size) {
		dev_WARN_ONCE(dev, 1,
			"Buffer overflow detected. Allocation size: %zu. Mapping size: %zu+%u.\n",
			alloc_size, size, tlb_offset);
		return;
	}

	orig_addr += tlb_offset;
	alloc_size -= tlb_offset;

	if (size > alloc_size) {
		dev_WARN_ONCE(dev, 1,
			"Buffer overflow detected. Allocation size: %zu. Mapping size: %zu.\n",
			alloc_size, size);
		size = alloc_size;
	}

	if (PageHighMem(pfn_to_page(pfn))) {
		unsigned int offset = orig_addr & ~PAGE_MASK;
		struct page *page;
		unsigned int sz = 0;
		unsigned long flags;

		while (size) {
			sz = min_t(size_t, PAGE_SIZE - offset, size);

			local_irq_save(flags);
			page = pfn_to_page(pfn);
			if (dir == DMA_TO_DEVICE)
				memcpy_from_page(vaddr, page, offset, sz);
			else
				memcpy_to_page(page, offset, vaddr, sz);
			local_irq_restore(flags);

			size -= sz;
			pfn++;
			vaddr += sz;
			offset = 0;
		}
	} else if (dir == DMA_TO_DEVICE) {
		memcpy(vaddr, phys_to_virt(orig_addr), size);
	} else {
		memcpy(phys_to_virt(orig_addr), vaddr, size);
	}
}

static inline phys_addr_t slot_addr(phys_addr_t start, phys_addr_t idx)
{
	return start + (idx << IO_TLB_SHIFT);
}

/*
 * Carefully handle integer overflow which can occur when boundary_mask == ~0UL.
 */
static inline unsigned long get_max_slots(unsigned long boundary_mask)
{
	return (boundary_mask >> IO_TLB_SHIFT) + 1;
}

static unsigned int wrap_area_index(struct io_tlb_pool *mem, unsigned int index)
{
	if (index >= mem->area_nslabs)
		return 0;
	return index;
}

/*
 * Track the total used slots with a global atomic value in order to have
 * correct information to determine the high water mark. The mem_used()
 * function gives imprecise results because there's no locking across
 * multiple areas.
 */
#ifdef CONFIG_DEBUG_FS
static void inc_used_and_hiwater(struct io_tlb_mem *mem, unsigned int nslots)
{
	unsigned long old_hiwater, new_used;

	new_used = atomic_long_add_return(nslots, &mem->total_used);
	old_hiwater = atomic_long_read(&mem->used_hiwater);
	do {
		if (new_used <= old_hiwater)
			break;
	} while (!atomic_long_try_cmpxchg(&mem->used_hiwater,
					  &old_hiwater, new_used));
}

static void dec_used(struct io_tlb_mem *mem, unsigned int nslots)
{
	atomic_long_sub(nslots, &mem->total_used);
}

#else /* !CONFIG_DEBUG_FS */
static void inc_used_and_hiwater(struct io_tlb_mem *mem, unsigned int nslots)
{
}
static void dec_used(struct io_tlb_mem *mem, unsigned int nslots)
{
}
#endif /* CONFIG_DEBUG_FS */

#ifdef CONFIG_SWIOTLB_DYNAMIC
#ifdef CONFIG_DEBUG_FS
static void inc_transient_used(struct io_tlb_mem *mem, unsigned int nslots)
{
	atomic_long_add(nslots, &mem->transient_nslabs);
}

static void dec_transient_used(struct io_tlb_mem *mem, unsigned int nslots)
{
	atomic_long_sub(nslots, &mem->transient_nslabs);
}

#else /* !CONFIG_DEBUG_FS */
static void inc_transient_used(struct io_tlb_mem *mem, unsigned int nslots)
{
}
static void dec_transient_used(struct io_tlb_mem *mem, unsigned int nslots)
{
}
#endif /* CONFIG_DEBUG_FS */
#endif /* CONFIG_SWIOTLB_DYNAMIC */

/**
 * swiotlb_search_pool_area() - search one memory area in one pool
 * @dev:	Device which maps the buffer.
 * @pool:	Memory pool to be searched.
 * @area_index:	Index of the IO TLB memory area to be searched.
 * @orig_addr:	Original (non-bounced) IO buffer address.
 * @alloc_size: Total requested size of the bounce buffer,
 *		including initial alignment padding.
 * @alloc_align_mask:	Required alignment of the allocated buffer.
 *
 * Find a suitable sequence of IO TLB entries for the request and allocate
 * a buffer from the given IO TLB memory area.
 * This function takes care of locking.
 *
 * Return: Index of the first allocated slot, or -1 on error.
 */
static int swiotlb_search_pool_area(struct device *dev, struct io_tlb_pool *pool,
		int area_index, phys_addr_t orig_addr, size_t alloc_size,
		unsigned int alloc_align_mask)
{
	struct io_tlb_area *area = pool->areas + area_index;
	unsigned long boundary_mask = dma_get_seg_boundary(dev);
	dma_addr_t tbl_dma_addr =
		phys_to_dma_unencrypted(dev, pool->start) & boundary_mask;
	unsigned long max_slots = get_max_slots(boundary_mask);
	unsigned int iotlb_align_mask = dma_get_min_align_mask(dev);
	unsigned int nslots = nr_slots(alloc_size), stride;
	unsigned int offset = swiotlb_align_offset(dev, orig_addr);
	unsigned int index, slots_checked, count = 0, i;
	unsigned long flags;
	unsigned int slot_base;
	unsigned int slot_index;

	BUG_ON(!nslots);
	BUG_ON(area_index >= pool->nareas);

	/*
	 * Historically, swiotlb allocations >= PAGE_SIZE were guaranteed to be
	 * page-aligned in the absence of any other alignment requirements.
	 * 'alloc_align_mask' was later introduced to specify the alignment
	 * explicitly, however this is passed as zero for streaming mappings
	 * and so we preserve the old behaviour there in case any drivers are
	 * relying on it.
	 */
	if (!alloc_align_mask && !iotlb_align_mask && alloc_size >= PAGE_SIZE)
		alloc_align_mask = PAGE_SIZE - 1;

	/*
	 * Ensure that the allocation is at least slot-aligned and update
	 * 'iotlb_align_mask' to ignore bits that will be preserved when
	 * offsetting into the allocation.
	 */
	alloc_align_mask |= (IO_TLB_SIZE - 1);
	iotlb_align_mask &= ~alloc_align_mask;

	/*
	 * For mappings with an alignment requirement don't bother looping to
	 * unaligned slots once we found an aligned one.
	 */
	stride = get_max_slots(max(alloc_align_mask, iotlb_align_mask));

	spin_lock_irqsave(&area->lock, flags);
	if (unlikely(nslots > pool->area_nslabs - area->used))
		goto not_found;

	slot_base = area_index * pool->area_nslabs;
	index = area->index;

	for (slots_checked = 0; slots_checked < pool->area_nslabs; ) {
		phys_addr_t tlb_addr;

		slot_index = slot_base + index;
		tlb_addr = slot_addr(tbl_dma_addr, slot_index);

		if ((tlb_addr & alloc_align_mask) ||
		    (orig_addr && (tlb_addr & iotlb_align_mask) !=
				  (orig_addr & iotlb_align_mask))) {
			index = wrap_area_index(pool, index + 1);
			slots_checked++;
			continue;
		}

		if (!iommu_is_span_boundary(slot_index, nslots,
					    nr_slots(tbl_dma_addr),
					    max_slots)) {
			if (pool->slots[slot_index].list >= nslots)
				goto found;
		}
		index = wrap_area_index(pool, index + stride);
		slots_checked += stride;
	}

not_found:
	spin_unlock_irqrestore(&area->lock, flags);
	return -1;

found:
	/*
	 * If we find a slot that indicates we have 'nslots' number of
	 * contiguous buffers, we allocate the buffers from that slot onwards
	 * and set the list of free entries to '0' indicating unavailable.
	 */
	for (i = slot_index; i < slot_index + nslots; i++) {
		pool->slots[i].list = 0;
		pool->slots[i].alloc_size = alloc_size - (offset +
				((i - slot_index) << IO_TLB_SHIFT));
	}
	for (i = slot_index - 1;
	     io_tlb_offset(i) != IO_TLB_SEGSIZE - 1 &&
	     pool->slots[i].list; i--)
		pool->slots[i].list = ++count;

	/*
	 * Update the indices to avoid searching in the next round.
	 */
	area->index = wrap_area_index(pool, index + nslots);
	area->used += nslots;
	spin_unlock_irqrestore(&area->lock, flags);

	inc_used_and_hiwater(dev->dma_io_tlb_mem, nslots);
	return slot_index;
}

#ifdef CONFIG_SWIOTLB_DYNAMIC

/**
 * swiotlb_search_area() - search one memory area in all pools
 * @dev:	Device which maps the buffer.
 * @start_cpu:	Start CPU number.
 * @cpu_offset:	Offset from @start_cpu.
 * @orig_addr:	Original (non-bounced) IO buffer address.
 * @alloc_size: Total requested size of the bounce buffer,
 *		including initial alignment padding.
 * @alloc_align_mask:	Required alignment of the allocated buffer.
 * @retpool:	Used memory pool, updated on return.
 *
 * Search one memory area in all pools for a sequence of slots that match the
 * allocation constraints.
 *
 * Return: Index of the first allocated slot, or -1 on error.
 */
static int swiotlb_search_area(struct device *dev, int start_cpu,
		int cpu_offset, phys_addr_t orig_addr, size_t alloc_size,
		unsigned int alloc_align_mask, struct io_tlb_pool **retpool)
{
	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
	struct io_tlb_pool *pool;
	int area_index;
	int index = -1;

	rcu_read_lock();
	list_for_each_entry_rcu(pool, &mem->pools, node) {
		if (cpu_offset >= pool->nareas)
			continue;
		area_index = (start_cpu + cpu_offset) & (pool->nareas - 1);
		index = swiotlb_search_pool_area(dev, pool, area_index,
						 orig_addr, alloc_size,
						 alloc_align_mask);
		if (index >= 0) {
			*retpool = pool;
			break;
		}
	}
	rcu_read_unlock();
	return index;
}

/**
 * swiotlb_find_slots() - search for slots in the whole swiotlb
 * @dev:	Device which maps the buffer.
 * @orig_addr:	Original (non-bounced) IO buffer address.
 * @alloc_size: Total requested size of the bounce buffer,
 *		including initial alignment padding.
 * @alloc_align_mask:	Required alignment of the allocated buffer.
 * @retpool:	Used memory pool, updated on return.
 *
 * Search through the whole software IO TLB to find a sequence of slots that
 * match the allocation constraints.
 *
 * Return: Index of the first allocated slot, or -1 on error.
 */
static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
		size_t alloc_size, unsigned int alloc_align_mask,
		struct io_tlb_pool **retpool)
{
	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
	struct io_tlb_pool *pool;
	unsigned long nslabs;
	unsigned long flags;
	u64 phys_limit;
	int cpu, i;
	int index;

	if (alloc_size > IO_TLB_SEGSIZE * IO_TLB_SIZE)
		return -1;

	cpu = raw_smp_processor_id();
	for (i = 0; i < default_nareas; ++i) {
		index = swiotlb_search_area(dev, cpu, i, orig_addr, alloc_size,
					    alloc_align_mask, &pool);
		if (index >= 0)
			goto found;
	}

	if (!mem->can_grow)
		return -1;

	schedule_work(&mem->dyn_alloc);

	nslabs = nr_slots(alloc_size);
	phys_limit = min_not_zero(*dev->dma_mask, dev->bus_dma_limit);
	pool = swiotlb_alloc_pool(dev, nslabs, nslabs, 1, phys_limit,
				  GFP_NOWAIT | __GFP_NOWARN);
	if (!pool)
		return -1;

	index = swiotlb_search_pool_area(dev, pool, 0, orig_addr,
					 alloc_size, alloc_align_mask);
	if (index < 0) {
		swiotlb_dyn_free(&pool->rcu);
		return -1;
	}

	pool->transient = true;
	spin_lock_irqsave(&dev->dma_io_tlb_lock, flags);
	list_add_rcu(&pool->node, &dev->dma_io_tlb_pools);
	spin_unlock_irqrestore(&dev->dma_io_tlb_lock, flags);
	inc_transient_used(mem, pool->nslabs);

found:
	WRITE_ONCE(dev->dma_uses_io_tlb, true);

	/*
	 * The general barrier orders reads and writes against a presumed store
	 * of the SWIOTLB buffer address by a device driver (to a driver private
	 * data structure). It serves two purposes.
	 *
	 * First, the store to dev->dma_uses_io_tlb must be ordered before the
	 * presumed store. This guarantees that the returned buffer address
	 * cannot be passed to another CPU before updating dev->dma_uses_io_tlb.
	 *
	 * Second, the load from mem->pools must be ordered before the same
	 * presumed store. This guarantees that the returned buffer address
	 * cannot be observed by another CPU before an update of the RCU list
	 * that was made by swiotlb_dyn_alloc() on a third CPU (cf. multicopy
	 * atomicity).
	 *
	 * See also the comment in is_swiotlb_buffer().
	 */
	smp_mb();

	*retpool = pool;
	return index;
}

#else  /* !CONFIG_SWIOTLB_DYNAMIC */

static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
		size_t alloc_size, unsigned int alloc_align_mask,
		struct io_tlb_pool **retpool)
{
	struct io_tlb_pool *pool;
	int start, i;
	int index;

	*retpool = pool = &dev->dma_io_tlb_mem->defpool;
	i = start = raw_smp_processor_id() & (pool->nareas - 1);
	do {
		index = swiotlb_search_pool_area(dev, pool, i, orig_addr,
						 alloc_size, alloc_align_mask);
		if (index >= 0)
			return index;
		if (++i >= pool->nareas)
			i = 0;
	} while (i != start);
	return -1;
}

#endif /* CONFIG_SWIOTLB_DYNAMIC */

#ifdef CONFIG_DEBUG_FS

/**
 * mem_used() - get number of used slots in an allocator
 * @mem:	Software IO TLB allocator.
 *
 * The result is accurate in this version of the function, because an atomic
 * counter is available if CONFIG_DEBUG_FS is set.
 *
 * Return: Number of used slots.
 */
static unsigned long mem_used(struct io_tlb_mem *mem)
{
	return atomic_long_read(&mem->total_used);
}

#else /* !CONFIG_DEBUG_FS */

/**
 * mem_pool_used() - get number of used slots in a memory pool
 * @pool:	Software IO TLB memory pool.
 *
 * The result is not accurate, see mem_used().
 *
 * Return: Approximate number of used slots.
 */
static unsigned long mem_pool_used(struct io_tlb_pool *pool)
{
	int i;
	unsigned long used = 0;

	for (i = 0; i < pool->nareas; i++)
		used += pool->areas[i].used;
	return used;
}

/**
 * mem_used() - get number of used slots in an allocator
 * @mem:	Software IO TLB allocator.
 *
 * The result is not accurate, because there is no locking of individual
 * areas.
 *
 * Return: Approximate number of used slots.
 */
static unsigned long mem_used(struct io_tlb_mem *mem)
{
#ifdef CONFIG_SWIOTLB_DYNAMIC
	struct io_tlb_pool *pool;
	unsigned long used = 0;

	rcu_read_lock();
	list_for_each_entry_rcu(pool, &mem->pools, node)
		used += mem_pool_used(pool);
	rcu_read_unlock();

	return used;
#else
	return mem_pool_used(&mem->defpool);
#endif
}

#endif /* CONFIG_DEBUG_FS */

phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
		size_t mapping_size, size_t alloc_size,
		unsigned int alloc_align_mask, enum dma_data_direction dir,
		unsigned long attrs)
{
	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
	unsigned int offset = swiotlb_align_offset(dev, orig_addr);
	struct io_tlb_pool *pool;
	unsigned int i;
	int index;
	phys_addr_t tlb_addr;

	if (!mem || !mem->nslabs) {
		dev_warn_ratelimited(dev,
			"Can not allocate SWIOTLB buffer earlier and can't now provide you with the DMA bounce buffer");
		return (phys_addr_t)DMA_MAPPING_ERROR;
	}

	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
		pr_warn_once("Memory encryption is active and system is using DMA bounce buffers\n");

	if (mapping_size > alloc_size) {
		dev_warn_once(dev, "Invalid sizes (mapping: %zd bytes, alloc: %zd bytes)",
			      mapping_size, alloc_size);
		return (phys_addr_t)DMA_MAPPING_ERROR;
	}

	index = swiotlb_find_slots(dev, orig_addr,
				   alloc_size + offset, alloc_align_mask, &pool);
	if (index == -1) {
		if (!(attrs & DMA_ATTR_NO_WARN))
			dev_warn_ratelimited(dev,
	"swiotlb buffer is full (sz: %zd bytes), total %lu (slots), used %lu (slots)\n",
				 alloc_size, mem->nslabs, mem_used(mem));
		return (phys_addr_t)DMA_MAPPING_ERROR;
	}

	/*
	 * Save away the mapping from the original address to the DMA address.
	 * This is needed when we sync the memory.  Then we sync the buffer if
	 * needed.
	 */
	for (i = 0; i < nr_slots(alloc_size + offset); i++)
		pool->slots[index + i].orig_addr = slot_addr(orig_addr, i);
	tlb_addr = slot_addr(pool->start, index) + offset;
	/*
	 * When the device is writing memory, i.e. dir == DMA_FROM_DEVICE, copy
	 * the original buffer to the TLB buffer before initiating DMA in order
	 * to preserve the original's data if the device does a partial write,
	 * i.e. if the device doesn't overwrite the entire buffer.  Preserving
	 * the original data, even if it's garbage, is necessary to match
	 * hardware behavior.  Use of swiotlb is supposed to be transparent,
	 * i.e. swiotlb must not corrupt memory by clobbering unwritten bytes.
	 */
	swiotlb_bounce(dev, tlb_addr, mapping_size, DMA_TO_DEVICE);
	return tlb_addr;
}

static void swiotlb_release_slots(struct device *dev, phys_addr_t tlb_addr)
{
	struct io_tlb_pool *mem = swiotlb_find_pool(dev, tlb_addr);
	unsigned long flags;
	unsigned int offset = swiotlb_align_offset(dev, tlb_addr);
	int index = (tlb_addr - offset - mem->start) >> IO_TLB_SHIFT;
	int nslots = nr_slots(mem->slots[index].alloc_size + offset);
	int aindex = index / mem->area_nslabs;
	struct io_tlb_area *area = &mem->areas[aindex];
	int count, i;

	/*
	 * Return the buffer to the free list by setting the corresponding
	 * entries to indicate the number of contiguous entries available.
	 * While returning the entries to the free list, we merge the entries
	 * with slots below and above the pool being returned.
	 */
	BUG_ON(aindex >= mem->nareas);

	spin_lock_irqsave(&area->lock, flags);
	if (index + nslots < ALIGN(index + 1, IO_TLB_SEGSIZE))
		count = mem->slots[index + nslots].list;
	else
		count = 0;

	/*
	 * Step 1: return the slots to the free list, merging the slots with
	 * superceeding slots
	 */
	for (i = index + nslots - 1; i >= index; i--) {
		mem->slots[i].list = ++count;
		mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
		mem->slots[i].alloc_size = 0;
	}

	/*
	 * Step 2: merge the returned slots with the preceding slots, if
	 * available (non zero)
	 */
	for (i = index - 1;
	     io_tlb_offset(i) != IO_TLB_SEGSIZE - 1 && mem->slots[i].list;
	     i--)
		mem->slots[i].list = ++count;
	area->used -= nslots;
	spin_unlock_irqrestore(&area->lock, flags);

	dec_used(dev->dma_io_tlb_mem, nslots);
}

#ifdef CONFIG_SWIOTLB_DYNAMIC

/**
 * swiotlb_del_transient() - delete a transient memory pool
 * @dev:	Device which mapped the buffer.
 * @tlb_addr:	Physical address within a bounce buffer.
 *
 * Check whether the address belongs to a transient SWIOTLB memory pool.
 * If yes, then delete the pool.
 *
 * Return: %true if @tlb_addr belonged to a transient pool that was released.
 */
static bool swiotlb_del_transient(struct device *dev, phys_addr_t tlb_addr)
{
	struct io_tlb_pool *pool;

	pool = swiotlb_find_pool(dev, tlb_addr);
	if (!pool->transient)
		return false;

	dec_used(dev->dma_io_tlb_mem, pool->nslabs);
	swiotlb_del_pool(dev, pool);
	dec_transient_used(dev->dma_io_tlb_mem, pool->nslabs);
	return true;
}

#else  /* !CONFIG_SWIOTLB_DYNAMIC */

static inline bool swiotlb_del_transient(struct device *dev,
					 phys_addr_t tlb_addr)
{
	return false;
}

#endif	/* CONFIG_SWIOTLB_DYNAMIC */

/*
 * tlb_addr is the physical address of the bounce buffer to unmap.
 */
void swiotlb_tbl_unmap_single(struct device *dev, phys_addr_t tlb_addr,
			      size_t mapping_size, enum dma_data_direction dir,
			      unsigned long attrs)
{
	/*
	 * First, sync the memory before unmapping the entry
	 */
	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
	    (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL))
		swiotlb_bounce(dev, tlb_addr, mapping_size, DMA_FROM_DEVICE);

	if (swiotlb_del_transient(dev, tlb_addr))
		return;
	swiotlb_release_slots(dev, tlb_addr);
}

void swiotlb_sync_single_for_device(struct device *dev, phys_addr_t tlb_addr,
		size_t size, enum dma_data_direction dir)
{
	if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
		swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
	else
		BUG_ON(dir != DMA_FROM_DEVICE);
}

void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_addr,
		size_t size, enum dma_data_direction dir)
{
	if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)
		swiotlb_bounce(dev, tlb_addr, size, DMA_FROM_DEVICE);
	else
		BUG_ON(dir != DMA_TO_DEVICE);
}

/*
 * Create a swiotlb mapping for the buffer at @paddr, and in case of DMAing
 * to the device copy the data into it as well.
 */
dma_addr_t swiotlb_map(struct device *dev, phys_addr_t paddr, size_t size,
		enum dma_data_direction dir, unsigned long attrs)
{
	phys_addr_t swiotlb_addr;
	dma_addr_t dma_addr;

	trace_swiotlb_bounced(dev, phys_to_dma(dev, paddr), size);

	swiotlb_addr = swiotlb_tbl_map_single(dev, paddr, size, size, 0, dir,
			attrs);
	if (swiotlb_addr == (phys_addr_t)DMA_MAPPING_ERROR)
		return DMA_MAPPING_ERROR;

	/* Ensure that the address returned is DMA'ble */
	dma_addr = phys_to_dma_unencrypted(dev, swiotlb_addr);
	if (unlikely(!dma_capable(dev, dma_addr, size, true))) {
		swiotlb_tbl_unmap_single(dev, swiotlb_addr, size, dir,
			attrs | DMA_ATTR_SKIP_CPU_SYNC);
		dev_WARN_ONCE(dev, 1,
			"swiotlb addr %pad+%zu overflow (mask %llx, bus limit %llx).\n",
			&dma_addr, size, *dev->dma_mask, dev->bus_dma_limit);
		return DMA_MAPPING_ERROR;
	}

	if (!dev_is_dma_coherent(dev) && !(attrs & DMA_ATTR_SKIP_CPU_SYNC))
		arch_sync_dma_for_device(swiotlb_addr, size, dir);
	return dma_addr;
}

size_t swiotlb_max_mapping_size(struct device *dev)
{
	int min_align_mask = dma_get_min_align_mask(dev);
	int min_align = 0;

	/*
	 * swiotlb_find_slots() skips slots according to
	 * min align mask. This affects max mapping size.
	 * Take it into acount here.
	 */
	if (min_align_mask)
		min_align = roundup(min_align_mask, IO_TLB_SIZE);

	return ((size_t)IO_TLB_SIZE) * IO_TLB_SEGSIZE - min_align;
}

/**
 * is_swiotlb_allocated() - check if the default software IO TLB is initialized
 */
bool is_swiotlb_allocated(void)
{
	return io_tlb_default_mem.nslabs;
}

bool is_swiotlb_active(struct device *dev)
{
	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;

	return mem && mem->nslabs;
}

/**
 * default_swiotlb_base() - get the base address of the default SWIOTLB
 *
 * Get the lowest physical address used by the default software IO TLB pool.
 */
phys_addr_t default_swiotlb_base(void)
{
#ifdef CONFIG_SWIOTLB_DYNAMIC
	io_tlb_default_mem.can_grow = false;
#endif
	return io_tlb_default_mem.defpool.start;
}

/**
 * default_swiotlb_limit() - get the address limit of the default SWIOTLB
 *
 * Get the highest physical address used by the default software IO TLB pool.
 */
phys_addr_t default_swiotlb_limit(void)
{
#ifdef CONFIG_SWIOTLB_DYNAMIC
	return io_tlb_default_mem.phys_limit;
#else
	return io_tlb_default_mem.defpool.end - 1;
#endif
}

#ifdef CONFIG_DEBUG_FS
#ifdef CONFIG_SWIOTLB_DYNAMIC
static unsigned long mem_transient_used(struct io_tlb_mem *mem)
{
	return atomic_long_read(&mem->transient_nslabs);
}

static int io_tlb_transient_used_get(void *data, u64 *val)
{
	struct io_tlb_mem *mem = data;

	*val = mem_transient_used(mem);
	return 0;
}

DEFINE_DEBUGFS_ATTRIBUTE(fops_io_tlb_transient_used, io_tlb_transient_used_get,
			 NULL, "%llu\n");
#endif /* CONFIG_SWIOTLB_DYNAMIC */

static int io_tlb_used_get(void *data, u64 *val)
{
	struct io_tlb_mem *mem = data;

	*val = mem_used(mem);
	return 0;
}

static int io_tlb_hiwater_get(void *data, u64 *val)
{
	struct io_tlb_mem *mem = data;

	*val = atomic_long_read(&mem->used_hiwater);
	return 0;
}

static int io_tlb_hiwater_set(void *data, u64 val)
{
	struct io_tlb_mem *mem = data;

	/* Only allow setting to zero */
	if (val != 0)
		return -EINVAL;

	atomic_long_set(&mem->used_hiwater, val);
	return 0;
}

DEFINE_DEBUGFS_ATTRIBUTE(fops_io_tlb_used, io_tlb_used_get, NULL, "%llu\n");
DEFINE_DEBUGFS_ATTRIBUTE(fops_io_tlb_hiwater, io_tlb_hiwater_get,
				io_tlb_hiwater_set, "%llu\n");

static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem,
					 const char *dirname)
{
	atomic_long_set(&mem->total_used, 0);
	atomic_long_set(&mem->used_hiwater, 0);

	mem->debugfs = debugfs_create_dir(dirname, io_tlb_default_mem.debugfs);
	if (!mem->nslabs)
		return;

	debugfs_create_ulong("io_tlb_nslabs", 0400, mem->debugfs, &mem->nslabs);
	debugfs_create_file("io_tlb_used", 0400, mem->debugfs, mem,
			&fops_io_tlb_used);
	debugfs_create_file("io_tlb_used_hiwater", 0600, mem->debugfs, mem,
			&fops_io_tlb_hiwater);
#ifdef CONFIG_SWIOTLB_DYNAMIC
	atomic_long_set(&mem->transient_nslabs, 0);
	debugfs_create_file("io_tlb_transient_nslabs", 0400, mem->debugfs,
			    mem, &fops_io_tlb_transient_used);
#endif
}

static int __init swiotlb_create_default_debugfs(void)
{
	swiotlb_create_debugfs_files(&io_tlb_default_mem, "swiotlb");
	return 0;
}

late_initcall(swiotlb_create_default_debugfs);

#else  /* !CONFIG_DEBUG_FS */

static inline void swiotlb_create_debugfs_files(struct io_tlb_mem *mem,
						const char *dirname)
{
}

#endif	/* CONFIG_DEBUG_FS */

#ifdef CONFIG_DMA_RESTRICTED_POOL

struct page *swiotlb_alloc(struct device *dev, size_t size)
{
	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
	struct io_tlb_pool *pool;
	phys_addr_t tlb_addr;
	unsigned int align;
	int index;

	if (!mem)
		return NULL;

	align = (1 << (get_order(size) + PAGE_SHIFT)) - 1;
	index = swiotlb_find_slots(dev, 0, size, align, &pool);
	if (index == -1)
		return NULL;

	tlb_addr = slot_addr(pool->start, index);
	if (unlikely(!PAGE_ALIGNED(tlb_addr))) {
		dev_WARN_ONCE(dev, 1, "Cannot allocate pages from non page-aligned swiotlb addr 0x%pa.\n",
			      &tlb_addr);
		swiotlb_release_slots(dev, tlb_addr);
		return NULL;
	}

	return pfn_to_page(PFN_DOWN(tlb_addr));
}

bool swiotlb_free(struct device *dev, struct page *page, size_t size)
{
	phys_addr_t tlb_addr = page_to_phys(page);

	if (!is_swiotlb_buffer(dev, tlb_addr))
		return false;

	swiotlb_release_slots(dev, tlb_addr);

	return true;
}

static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
				    struct device *dev)
{
	struct io_tlb_mem *mem = rmem->priv;
	unsigned long nslabs = rmem->size >> IO_TLB_SHIFT;

	/* Set Per-device io tlb area to one */
	unsigned int nareas = 1;

	if (PageHighMem(pfn_to_page(PHYS_PFN(rmem->base)))) {
		dev_err(dev, "Restricted DMA pool must be accessible within the linear mapping.");
		return -EINVAL;
	}

	/*
	 * Since multiple devices can share the same pool, the private data,
	 * io_tlb_mem struct, will be initialized by the first device attached
	 * to it.
	 */
	if (!mem) {
		struct io_tlb_pool *pool;

		mem = kzalloc(sizeof(*mem), GFP_KERNEL);
		if (!mem)
			return -ENOMEM;
		pool = &mem->defpool;

		pool->slots = kcalloc(nslabs, sizeof(*pool->slots), GFP_KERNEL);
		if (!pool->slots) {
			kfree(mem);
			return -ENOMEM;
		}

		pool->areas = kcalloc(nareas, sizeof(*pool->areas),
				GFP_KERNEL);
		if (!pool->areas) {
			kfree(pool->slots);
			kfree(mem);
			return -ENOMEM;
		}

		set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
				     rmem->size >> PAGE_SHIFT);
		swiotlb_init_io_tlb_pool(pool, rmem->base, nslabs,
					 false, nareas);
		mem->force_bounce = true;
		mem->for_alloc = true;
#ifdef CONFIG_SWIOTLB_DYNAMIC
		spin_lock_init(&mem->lock);
#endif
		add_mem_pool(mem, pool);

		rmem->priv = mem;

		swiotlb_create_debugfs_files(mem, rmem->name);
	}

	dev->dma_io_tlb_mem = mem;

	return 0;
}

static void rmem_swiotlb_device_release(struct reserved_mem *rmem,
					struct device *dev)
{
	dev->dma_io_tlb_mem = &io_tlb_default_mem;
}

static const struct reserved_mem_ops rmem_swiotlb_ops = {
	.device_init = rmem_swiotlb_device_init,
	.device_release = rmem_swiotlb_device_release,
};

static int __init rmem_swiotlb_setup(struct reserved_mem *rmem)
{
	unsigned long node = rmem->fdt_node;

	if (of_get_flat_dt_prop(node, "reusable", NULL) ||
	    of_get_flat_dt_prop(node, "linux,cma-default", NULL) ||
	    of_get_flat_dt_prop(node, "linux,dma-default", NULL) ||
	    of_get_flat_dt_prop(node, "no-map", NULL))
		return -EINVAL;

	rmem->ops = &rmem_swiotlb_ops;
	pr_info("Reserved memory: created restricted DMA pool at %pa, size %ld MiB\n",
		&rmem->base, (unsigned long)rmem->size / SZ_1M);
	return 0;
}

RESERVEDMEM_OF_DECLARE(dma, "restricted-dma-pool", rmem_swiotlb_setup);
#endif /* CONFIG_DMA_RESTRICTED_POOL */