arch/powerpc/lib/dma-noncoherent.c - kernel/msm-4.19 - Gitiles

 /*
  *  PowerPC version derived from arch/arm/mm/consistent.c
  *    Copyright (C) 2001 Dan Malek (dmalek@jlc.net)
  *
  *  Copyright (C) 2000 Russell King
  *
  * Consistent memory allocators.  Used for DMA devices that want to
  * share uncached memory with the processor core.  The function return
  * is the virtual address and 'dma_handle' is the physical address.
  * Mostly stolen from the ARM port, with some changes for PowerPC.
  *						-- Dan
  *
  * Reorganized to get rid of the arch-specific consistent_* functions
  * and provide non-coherent implementations for the DMA API. -Matt
  *
  * Added in_interrupt() safe dma_alloc_coherent()/dma_free_coherent()
  * implementation. This is pulled straight from ARM and barely
  * modified. -Matt
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */

 #include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/highmem.h>
 #include <linux/dma-mapping.h>

 #include <asm/tlbflush.h>

 /*
  * This address range defaults to a value that is safe for all
  * platforms which currently set CONFIG_NOT_COHERENT_CACHE. It
  * can be further configured for specific applications under
  * the "Advanced Setup" menu. -Matt
  */
 #define CONSISTENT_BASE	(CONFIG_CONSISTENT_START)
 #define CONSISTENT_END	(CONFIG_CONSISTENT_START + CONFIG_CONSISTENT_SIZE)
 #define CONSISTENT_OFFSET(x)	(((unsigned long)(x) - CONSISTENT_BASE) >> PAGE_SHIFT)

 /*
  * This is the page table (2MB) covering uncached, DMA consistent allocations
  */
 static pte_t *consistent_pte;
 static DEFINE_SPINLOCK(consistent_lock);

 /*
  * VM region handling support.
  *
  * This should become something generic, handling VM region allocations for
  * vmalloc and similar (ioremap, module space, etc).
  *
  * I envisage vmalloc()'s supporting vm_struct becoming:
  *
  *  struct vm_struct {
  *    struct vm_region	region;
  *    unsigned long	flags;
  *    struct page	**pages;
  *    unsigned int	nr_pages;
  *    unsigned long	phys_addr;
  *  };
  *
  * get_vm_area() would then call vm_region_alloc with an appropriate
  * struct vm_region head (eg):
  *
  *  struct vm_region vmalloc_head = {
  *	.vm_list	= LIST_HEAD_INIT(vmalloc_head.vm_list),
  *	.vm_start	= VMALLOC_START,
  *	.vm_end		= VMALLOC_END,
  *  };
  *
  * However, vmalloc_head.vm_start is variable (typically, it is dependent on
  * the amount of RAM found at boot time.)  I would imagine that get_vm_area()
  * would have to initialise this each time prior to calling vm_region_alloc().
  */
 struct ppc_vm_region {
 	struct list_head	vm_list;
 	unsigned long		vm_start;
 	unsigned long		vm_end;
 };

 static struct ppc_vm_region consistent_head = {
 	.vm_list	= LIST_HEAD_INIT(consistent_head.vm_list),
 	.vm_start	= CONSISTENT_BASE,
 	.vm_end		= CONSISTENT_END,
 };

 static struct ppc_vm_region *
 ppc_vm_region_alloc(struct ppc_vm_region *head, size_t size, gfp_t gfp)
 {
 	unsigned long addr = head->vm_start, end = head->vm_end - size;
 	unsigned long flags;
 	struct ppc_vm_region *c, *new;

 	new = kmalloc(sizeof(struct ppc_vm_region), gfp);
 	if (!new)
 		goto out;

 	spin_lock_irqsave(&consistent_lock, flags);

 	list_for_each_entry(c, &head->vm_list, vm_list) {
 		if ((addr + size) < addr)
 			goto nospc;
 		if ((addr + size) <= c->vm_start)
 			goto found;
 		addr = c->vm_end;
 		if (addr > end)
 			goto nospc;
 	}

  found:
 	/*
 	 * Insert this entry _before_ the one we found.
 	 */
 	list_add_tail(&new->vm_list, &c->vm_list);
 	new->vm_start = addr;
 	new->vm_end = addr + size;

 	spin_unlock_irqrestore(&consistent_lock, flags);
 	return new;

  nospc:
 	spin_unlock_irqrestore(&consistent_lock, flags);
 	kfree(new);
  out:
 	return NULL;
 }

 static struct ppc_vm_region *ppc_vm_region_find(struct ppc_vm_region *head, unsigned long addr)
 {
 	struct ppc_vm_region *c;

 	list_for_each_entry(c, &head->vm_list, vm_list) {
 		if (c->vm_start == addr)
 			goto out;
 	}
 	c = NULL;
  out:
 	return c;
 }

 /*
  * Allocate DMA-coherent memory space and return both the kernel remapped
  * virtual and bus address for that space.
  */
 void *
 __dma_alloc_coherent(size_t size, dma_addr_t *handle, gfp_t gfp)
 {
 	struct page *page;
 	struct ppc_vm_region *c;
 	unsigned long order;
 	u64 mask = 0x00ffffff, limit; /* ISA default */

 	if (!consistent_pte) {
 		printk(KERN_ERR "%s: not initialised\n", __func__);
 		dump_stack();
 		return NULL;
 	}

 	size = PAGE_ALIGN(size);
 	limit = (mask + 1) & ~mask;
 	if ((limit && size >= limit) || size >= (CONSISTENT_END - CONSISTENT_BASE)) {
 		printk(KERN_WARNING "coherent allocation too big (requested %#x mask %#Lx)\n",
 		       size, mask);
 		return NULL;
 	}

 	order = get_order(size);

 	if (mask != 0xffffffff)
 		gfp |= GFP_DMA;

 	page = alloc_pages(gfp, order);
 	if (!page)
 		goto no_page;

 	/*
 	 * Invalidate any data that might be lurking in the
 	 * kernel direct-mapped region for device DMA.
 	 */
 	{
 		unsigned long kaddr = (unsigned long)page_address(page);
 		memset(page_address(page), 0, size);
 		flush_dcache_range(kaddr, kaddr + size);
 	}

 	/*
 	 * Allocate a virtual address in the consistent mapping region.
 	 */
 	c = ppc_vm_region_alloc(&consistent_head, size,
 			    gfp & ~(__GFP_DMA | __GFP_HIGHMEM));
 	if (c) {
 		unsigned long vaddr = c->vm_start;
 		pte_t *pte = consistent_pte + CONSISTENT_OFFSET(vaddr);
 		struct page *end = page + (1 << order);

 		split_page(page, order);

 		/*
 		 * Set the "dma handle"
 		 */
 		*handle = page_to_phys(page);

 		do {
 			BUG_ON(!pte_none(*pte));

 			SetPageReserved(page);
 			set_pte_at(&init_mm, vaddr,
 				   pte, mk_pte(page, pgprot_noncached(PAGE_KERNEL)));
 			page++;
 			pte++;
 			vaddr += PAGE_SIZE;
 		} while (size -= PAGE_SIZE);

 		/*
 		 * Free the otherwise unused pages.
 		 */
 		while (page < end) {
 			__free_page(page);
 			page++;
 		}

 		return (void *)c->vm_start;
 	}

 	if (page)
 		__free_pages(page, order);
  no_page:
 	return NULL;
 }
 EXPORT_SYMBOL(__dma_alloc_coherent);

 /*
  * free a page as defined by the above mapping.
  */
 void __dma_free_coherent(size_t size, void *vaddr)
 {
 	struct ppc_vm_region *c;
 	unsigned long flags, addr;
 	pte_t *ptep;

 	size = PAGE_ALIGN(size);

 	spin_lock_irqsave(&consistent_lock, flags);

 	c = ppc_vm_region_find(&consistent_head, (unsigned long)vaddr);
 	if (!c)
 		goto no_area;

 	if ((c->vm_end - c->vm_start) != size) {
 		printk(KERN_ERR "%s: freeing wrong coherent size (%ld != %d)\n",
 		       __func__, c->vm_end - c->vm_start, size);
 		dump_stack();
 		size = c->vm_end - c->vm_start;
 	}

 	ptep = consistent_pte + CONSISTENT_OFFSET(c->vm_start);
 	addr = c->vm_start;
 	do {
 		pte_t pte = ptep_get_and_clear(&init_mm, addr, ptep);
 		unsigned long pfn;

 		ptep++;
 		addr += PAGE_SIZE;

 		if (!pte_none(pte) && pte_present(pte)) {
 			pfn = pte_pfn(pte);

 			if (pfn_valid(pfn)) {
 				struct page *page = pfn_to_page(pfn);
 				ClearPageReserved(page);

 				__free_page(page);
 				continue;
 			}
 		}

 		printk(KERN_CRIT "%s: bad page in kernel page table\n",
 		       __func__);
 	} while (size -= PAGE_SIZE);

 	flush_tlb_kernel_range(c->vm_start, c->vm_end);

 	list_del(&c->vm_list);

 	spin_unlock_irqrestore(&consistent_lock, flags);

 	kfree(c);
 	return;

  no_area:
 	spin_unlock_irqrestore(&consistent_lock, flags);
 	printk(KERN_ERR "%s: trying to free invalid coherent area: %p\n",
 	       __func__, vaddr);
 	dump_stack();
 }
 EXPORT_SYMBOL(__dma_free_coherent);

 /*
  * Initialise the consistent memory allocation.
  */
 static int __init dma_alloc_init(void)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;
 	int ret = 0;

 	do {
 		pgd = pgd_offset(&init_mm, CONSISTENT_BASE);
 		pud = pud_alloc(&init_mm, pgd, CONSISTENT_BASE);
 		pmd = pmd_alloc(&init_mm, pud, CONSISTENT_BASE);
 		if (!pmd) {
 			printk(KERN_ERR "%s: no pmd tables\n", __func__);
 			ret = -ENOMEM;
 			break;
 		}

 		pte = pte_alloc_kernel(pmd, CONSISTENT_BASE);
 		if (!pte) {
 			printk(KERN_ERR "%s: no pte tables\n", __func__);
 			ret = -ENOMEM;
 			break;
 		}

 		consistent_pte = pte;
 	} while (0);

 	return ret;
 }

 core_initcall(dma_alloc_init);

 /*
  * make an area consistent.
  */
 void __dma_sync(void *vaddr, size_t size, int direction)
 {
 	unsigned long start = (unsigned long)vaddr;
 	unsigned long end   = start + size;

 	switch (direction) {
 	case DMA_NONE:
 		BUG();
 	case DMA_FROM_DEVICE:
 		/*
 		 * invalidate only when cache-line aligned otherwise there is
 		 * the potential for discarding uncommitted data from the cache
 		 */
 		if ((start & (L1_CACHE_BYTES - 1)) || (size & (L1_CACHE_BYTES - 1)))
 			flush_dcache_range(start, end);
 		else
 			invalidate_dcache_range(start, end);
 		break;
 	case DMA_TO_DEVICE:		/* writeback only */
 		clean_dcache_range(start, end);
 		break;
 	case DMA_BIDIRECTIONAL:	/* writeback and invalidate */
 		flush_dcache_range(start, end);
 		break;
 	}
 }
 EXPORT_SYMBOL(__dma_sync);

 #ifdef CONFIG_HIGHMEM
 /*
  * __dma_sync_page() implementation for systems using highmem.
  * In this case, each page of a buffer must be kmapped/kunmapped
  * in order to have a virtual address for __dma_sync(). This must
  * not sleep so kmap_atomic()/kunmap_atomic() are used.
  *
  * Note: yes, it is possible and correct to have a buffer extend
  * beyond the first page.
  */
 static inline void __dma_sync_page_highmem(struct page *page,
 		unsigned long offset, size_t size, int direction)
 {
 	size_t seg_size = min((size_t)(PAGE_SIZE - offset), size);
 	size_t cur_size = seg_size;
 	unsigned long flags, start, seg_offset = offset;
 	int nr_segs = 1 + ((size - seg_size) + PAGE_SIZE - 1)/PAGE_SIZE;
 	int seg_nr = 0;

 	local_irq_save(flags);

 	do {
 		start = (unsigned long)kmap_atomic(page + seg_nr,
 				KM_PPC_SYNC_PAGE) + seg_offset;

 		/* Sync this buffer segment */
 		__dma_sync((void *)start, seg_size, direction);
 		kunmap_atomic((void *)start, KM_PPC_SYNC_PAGE);
 		seg_nr++;

 		/* Calculate next buffer segment size */
 		seg_size = min((size_t)PAGE_SIZE, size - cur_size);

 		/* Add the segment size to our running total */
 		cur_size += seg_size;
 		seg_offset = 0;
 	} while (seg_nr < nr_segs);

 	local_irq_restore(flags);
 }
 #endif /* CONFIG_HIGHMEM */

 /*
  * __dma_sync_page makes memory consistent. identical to __dma_sync, but
  * takes a struct page instead of a virtual address
  */
 void __dma_sync_page(struct page *page, unsigned long offset,
 	size_t size, int direction)
 {
 #ifdef CONFIG_HIGHMEM
 	__dma_sync_page_highmem(page, offset, size, direction);
 #else
 	unsigned long start = (unsigned long)page_address(page) + offset;
 	__dma_sync((void *)start, size, direction);
 #endif
 }
 EXPORT_SYMBOL(__dma_sync_page);
	/*
	* PowerPC version derived from arch/arm/mm/consistent.c
	* Copyright (C) 2001 Dan Malek (dmalek@jlc.net)
	*
	* Copyright (C) 2000 Russell King
	*
	* Consistent memory allocators. Used for DMA devices that want to
	* share uncached memory with the processor core. The function return
	* is the virtual address and 'dma_handle' is the physical address.
	* Mostly stolen from the ARM port, with some changes for PowerPC.
	* -- Dan
	*
	* Reorganized to get rid of the arch-specific consistent_* functions
	* and provide non-coherent implementations for the DMA API. -Matt
	*
	* Added in_interrupt() safe dma_alloc_coherent()/dma_free_coherent()
	* implementation. This is pulled straight from ARM and barely
	* modified. -Matt
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*/

	#include <linux/sched.h>
	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/highmem.h>
	#include <linux/dma-mapping.h>

	#include <asm/tlbflush.h>

	/*
	* This address range defaults to a value that is safe for all
	* platforms which currently set CONFIG_NOT_COHERENT_CACHE. It
	* can be further configured for specific applications under
	* the "Advanced Setup" menu. -Matt
	*/
	#define CONSISTENT_BASE (CONFIG_CONSISTENT_START)
	#define CONSISTENT_END (CONFIG_CONSISTENT_START + CONFIG_CONSISTENT_SIZE)
	#define CONSISTENT_OFFSET(x) (((unsigned long)(x) - CONSISTENT_BASE) >> PAGE_SHIFT)

	/*
	* This is the page table (2MB) covering uncached, DMA consistent allocations
	*/
	static pte_t *consistent_pte;
	static DEFINE_SPINLOCK(consistent_lock);

	/*
	* VM region handling support.
	*
	* This should become something generic, handling VM region allocations for
	* vmalloc and similar (ioremap, module space, etc).
	*
	* I envisage vmalloc()'s supporting vm_struct becoming:
	*
	* struct vm_struct {
	* struct vm_region region;
	* unsigned long flags;
	* struct page **pages;
	* unsigned int nr_pages;
	* unsigned long phys_addr;
	* };
	*
	* get_vm_area() would then call vm_region_alloc with an appropriate
	* struct vm_region head (eg):
	*
	* struct vm_region vmalloc_head = {
	* .vm_list = LIST_HEAD_INIT(vmalloc_head.vm_list),
	* .vm_start = VMALLOC_START,
	* .vm_end = VMALLOC_END,
	* };
	*
	* However, vmalloc_head.vm_start is variable (typically, it is dependent on
	* the amount of RAM found at boot time.) I would imagine that get_vm_area()
	* would have to initialise this each time prior to calling vm_region_alloc().
	*/
	struct ppc_vm_region {
	struct list_head vm_list;
	unsigned long vm_start;
	unsigned long vm_end;
	};

	static struct ppc_vm_region consistent_head = {
	.vm_list = LIST_HEAD_INIT(consistent_head.vm_list),
	.vm_start = CONSISTENT_BASE,
	.vm_end = CONSISTENT_END,
	};

	static struct ppc_vm_region *
	ppc_vm_region_alloc(struct ppc_vm_region *head, size_t size, gfp_t gfp)
	{
	unsigned long addr = head->vm_start, end = head->vm_end - size;
	unsigned long flags;
	struct ppc_vm_region c, new;

	new = kmalloc(sizeof(struct ppc_vm_region), gfp);
	if (!new)
	goto out;

	spin_lock_irqsave(&consistent_lock, flags);

	list_for_each_entry(c, &head->vm_list, vm_list) {
	if ((addr + size) < addr)
	goto nospc;
	if ((addr + size) <= c->vm_start)
	goto found;
	addr = c->vm_end;
	if (addr > end)
	goto nospc;
	}

	found:
	/*
	* Insert this entry _before_ the one we found.
	*/
	list_add_tail(&new->vm_list, &c->vm_list);
	new->vm_start = addr;
	new->vm_end = addr + size;

	spin_unlock_irqrestore(&consistent_lock, flags);
	return new;

	nospc:
	spin_unlock_irqrestore(&consistent_lock, flags);
	kfree(new);
	out:
	return NULL;
	}

	static struct ppc_vm_region ppc_vm_region_find(struct ppc_vm_region head, unsigned long addr)
	{
	struct ppc_vm_region *c;

	list_for_each_entry(c, &head->vm_list, vm_list) {
	if (c->vm_start == addr)
	goto out;
	}
	c = NULL;
	out:
	return c;
	}

	/*
	* Allocate DMA-coherent memory space and return both the kernel remapped
	* virtual and bus address for that space.
	*/
	void *
	__dma_alloc_coherent(size_t size, dma_addr_t *handle, gfp_t gfp)
	{
	struct page *page;
	struct ppc_vm_region *c;
	unsigned long order;
	u64 mask = 0x00ffffff, limit; /* ISA default */

	if (!consistent_pte) {
	printk(KERN_ERR "%s: not initialised\n", __func__);
	dump_stack();
	return NULL;
	}

	size = PAGE_ALIGN(size);
	limit = (mask + 1) & ~mask;
	if ((limit && size >= limit) \|\| size >= (CONSISTENT_END - CONSISTENT_BASE)) {
	printk(KERN_WARNING "coherent allocation too big (requested %#x mask %#Lx)\n",
	size, mask);
	return NULL;
	}

	order = get_order(size);

	if (mask != 0xffffffff)
	gfp \|= GFP_DMA;

	page = alloc_pages(gfp, order);
	if (!page)
	goto no_page;

	/*
	* Invalidate any data that might be lurking in the
	* kernel direct-mapped region for device DMA.
	*/
	{
	unsigned long kaddr = (unsigned long)page_address(page);
	memset(page_address(page), 0, size);
	flush_dcache_range(kaddr, kaddr + size);
	}

	/*
	* Allocate a virtual address in the consistent mapping region.
	*/
	c = ppc_vm_region_alloc(&consistent_head, size,
	gfp & ~(__GFP_DMA \| __GFP_HIGHMEM));
	if (c) {
	unsigned long vaddr = c->vm_start;
	pte_t *pte = consistent_pte + CONSISTENT_OFFSET(vaddr);
	struct page *end = page + (1 << order);

	split_page(page, order);

	/*
	* Set the "dma handle"
	*/
	*handle = page_to_phys(page);

	do {
	BUG_ON(!pte_none(*pte));

	SetPageReserved(page);
	set_pte_at(&init_mm, vaddr,
	pte, mk_pte(page, pgprot_noncached(PAGE_KERNEL)));
	page++;
	pte++;
	vaddr += PAGE_SIZE;
	} while (size -= PAGE_SIZE);

	/*
	* Free the otherwise unused pages.
	*/
	while (page < end) {
	__free_page(page);
	page++;
	}

	return (void *)c->vm_start;
	}

	if (page)
	__free_pages(page, order);
	no_page:
	return NULL;
	}
	EXPORT_SYMBOL(__dma_alloc_coherent);

	/*
	* free a page as defined by the above mapping.
	*/
	void __dma_free_coherent(size_t size, void *vaddr)
	{
	struct ppc_vm_region *c;
	unsigned long flags, addr;
	pte_t *ptep;

	size = PAGE_ALIGN(size);

	spin_lock_irqsave(&consistent_lock, flags);

	c = ppc_vm_region_find(&consistent_head, (unsigned long)vaddr);
	if (!c)
	goto no_area;

	if ((c->vm_end - c->vm_start) != size) {
	printk(KERN_ERR "%s: freeing wrong coherent size (%ld != %d)\n",
	__func__, c->vm_end - c->vm_start, size);
	dump_stack();
	size = c->vm_end - c->vm_start;
	}

	ptep = consistent_pte + CONSISTENT_OFFSET(c->vm_start);
	addr = c->vm_start;
	do {
	pte_t pte = ptep_get_and_clear(&init_mm, addr, ptep);
	unsigned long pfn;

	ptep++;
	addr += PAGE_SIZE;

	if (!pte_none(pte) && pte_present(pte)) {
	pfn = pte_pfn(pte);

	if (pfn_valid(pfn)) {
	struct page *page = pfn_to_page(pfn);
	ClearPageReserved(page);

	__free_page(page);
	continue;
	}
	}

	printk(KERN_CRIT "%s: bad page in kernel page table\n",
	__func__);
	} while (size -= PAGE_SIZE);

	flush_tlb_kernel_range(c->vm_start, c->vm_end);

	list_del(&c->vm_list);

	spin_unlock_irqrestore(&consistent_lock, flags);

	kfree(c);
	return;

	no_area:
	spin_unlock_irqrestore(&consistent_lock, flags);
	printk(KERN_ERR "%s: trying to free invalid coherent area: %p\n",
	__func__, vaddr);
	dump_stack();
	}
	EXPORT_SYMBOL(__dma_free_coherent);

	/*
	* Initialise the consistent memory allocation.
	*/
	static int __init dma_alloc_init(void)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
	int ret = 0;

	do {
	pgd = pgd_offset(&init_mm, CONSISTENT_BASE);
	pud = pud_alloc(&init_mm, pgd, CONSISTENT_BASE);
	pmd = pmd_alloc(&init_mm, pud, CONSISTENT_BASE);
	if (!pmd) {
	printk(KERN_ERR "%s: no pmd tables\n", __func__);
	ret = -ENOMEM;
	break;
	}

	pte = pte_alloc_kernel(pmd, CONSISTENT_BASE);
	if (!pte) {
	printk(KERN_ERR "%s: no pte tables\n", __func__);
	ret = -ENOMEM;
	break;
	}

	consistent_pte = pte;
	} while (0);

	return ret;
	}

	core_initcall(dma_alloc_init);

	/*
	* make an area consistent.
	*/
	void __dma_sync(void *vaddr, size_t size, int direction)
	{
	unsigned long start = (unsigned long)vaddr;
	unsigned long end = start + size;

	switch (direction) {
	case DMA_NONE:
	BUG();
	case DMA_FROM_DEVICE:
	/*
	* invalidate only when cache-line aligned otherwise there is
	* the potential for discarding uncommitted data from the cache
	*/
	if ((start & (L1_CACHE_BYTES - 1)) \|\| (size & (L1_CACHE_BYTES - 1)))
	flush_dcache_range(start, end);
	else
	invalidate_dcache_range(start, end);
	break;
	case DMA_TO_DEVICE: /* writeback only */
	clean_dcache_range(start, end);
	break;
	case DMA_BIDIRECTIONAL: /* writeback and invalidate */
	flush_dcache_range(start, end);
	break;
	}
	}
	EXPORT_SYMBOL(__dma_sync);

	#ifdef CONFIG_HIGHMEM
	/*
	* __dma_sync_page() implementation for systems using highmem.
	* In this case, each page of a buffer must be kmapped/kunmapped
	* in order to have a virtual address for __dma_sync(). This must
	* not sleep so kmap_atomic()/kunmap_atomic() are used.
	*
	* Note: yes, it is possible and correct to have a buffer extend
	* beyond the first page.
	*/
	static inline void __dma_sync_page_highmem(struct page *page,
	unsigned long offset, size_t size, int direction)
	{
	size_t seg_size = min((size_t)(PAGE_SIZE - offset), size);
	size_t cur_size = seg_size;
	unsigned long flags, start, seg_offset = offset;
	int nr_segs = 1 + ((size - seg_size) + PAGE_SIZE - 1)/PAGE_SIZE;
	int seg_nr = 0;

	local_irq_save(flags);

	do {
	start = (unsigned long)kmap_atomic(page + seg_nr,
	KM_PPC_SYNC_PAGE) + seg_offset;

	/* Sync this buffer segment */
	__dma_sync((void *)start, seg_size, direction);
	kunmap_atomic((void *)start, KM_PPC_SYNC_PAGE);
	seg_nr++;

	/* Calculate next buffer segment size */
	seg_size = min((size_t)PAGE_SIZE, size - cur_size);

	/* Add the segment size to our running total */
	cur_size += seg_size;
	seg_offset = 0;
	} while (seg_nr < nr_segs);

	local_irq_restore(flags);
	}
	#endif /* CONFIG_HIGHMEM */

	/*
	* __dma_sync_page makes memory consistent. identical to __dma_sync, but
	* takes a struct page instead of a virtual address
	*/
	void __dma_sync_page(struct page *page, unsigned long offset,
	size_t size, int direction)
	{
	#ifdef CONFIG_HIGHMEM
	__dma_sync_page_highmem(page, offset, size, direction);
	#else
	unsigned long start = (unsigned long)page_address(page) + offset;
	__dma_sync((void *)start, size, direction);
	#endif
	}
	EXPORT_SYMBOL(__dma_sync_page);