drivers/media/v4l2-core/videobuf-dma-contig.c - maze/linux - Git at Google

 /*
  * helper functions for physically contiguous capture buffers
  *
  * The functions support hardware lacking scatter gather support
  * (i.e. the buffers must be linear in physical memory)
  *
  * Copyright (c) 2008 Magnus Damm
  *
  * Based on videobuf-vmalloc.c,
  * (c) 2007 Mauro Carvalho Chehab, <mchehab@infradead.org>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2
  */

 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/dma-mapping.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <media/videobuf-dma-contig.h>

 struct videobuf_dma_contig_memory {
 	u32 magic;
 	void *vaddr;
 	dma_addr_t dma_handle;
 	unsigned long size;
 };

 #define MAGIC_DC_MEM 0x0733ac61
 #define MAGIC_CHECK(is, should)						    \
 	if (unlikely((is) != (should)))	{				    \
 		pr_err("magic mismatch: %x expected %x\n", (is), (should)); \
 		BUG();							    \
 	}

 static int __videobuf_dc_alloc(struct device *dev,
 			       struct videobuf_dma_contig_memory *mem,
 			       unsigned long size, gfp_t flags)
 {
 	mem->size = size;
 	mem->vaddr = dma_alloc_coherent(dev, mem->size,
 					&mem->dma_handle, flags);

 	if (!mem->vaddr) {
 		dev_err(dev, "memory alloc size %ld failed\n", mem->size);
 		return -ENOMEM;
 	}

 	dev_dbg(dev, "dma mapped data is at %p (%ld)\n", mem->vaddr, mem->size);

 	return 0;
 }

 static void __videobuf_dc_free(struct device *dev,
 			       struct videobuf_dma_contig_memory *mem)
 {
 	dma_free_coherent(dev, mem->size, mem->vaddr, mem->dma_handle);

 	mem->vaddr = NULL;
 }

 static void videobuf_vm_open(struct vm_area_struct *vma)
 {
 	struct videobuf_mapping *map = vma->vm_private_data;
 	struct videobuf_queue *q = map->q;

 	dev_dbg(q->dev, "vm_open %p [count=%u,vma=%08lx-%08lx]\n",
 		map, map->count, vma->vm_start, vma->vm_end);

 	videobuf_queue_lock(q);
 	map->count++;
 	videobuf_queue_unlock(q);
 }

 static void videobuf_vm_close(struct vm_area_struct *vma)
 {
 	struct videobuf_mapping *map = vma->vm_private_data;
 	struct videobuf_queue *q = map->q;
 	int i;

 	dev_dbg(q->dev, "vm_close %p [count=%u,vma=%08lx-%08lx]\n",
 		map, map->count, vma->vm_start, vma->vm_end);

 	videobuf_queue_lock(q);
 	if (!--map->count) {
 		struct videobuf_dma_contig_memory *mem;

 		dev_dbg(q->dev, "munmap %p q=%p\n", map, q);

 		/* We need first to cancel streams, before unmapping */
 		if (q->streaming)
 			videobuf_queue_cancel(q);

 		for (i = 0; i < VIDEO_MAX_FRAME; i++) {
 			if (NULL == q->bufs[i])
 				continue;

 			if (q->bufs[i]->map != map)
 				continue;

 			mem = q->bufs[i]->priv;
 			if (mem) {
 				/* This callback is called only if kernel has
 				   allocated memory and this memory is mmapped.
 				   In this case, memory should be freed,
 				   in order to do memory unmap.
 				 */

 				MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

 				/* vfree is not atomic - can't be
 				   called with IRQ's disabled
 				 */
 				dev_dbg(q->dev, "buf[%d] freeing %p\n",
 					i, mem->vaddr);

 				__videobuf_dc_free(q->dev, mem);
 				mem->vaddr = NULL;
 			}

 			q->bufs[i]->map = NULL;
 			q->bufs[i]->baddr = 0;
 		}

 		kfree(map);

 	}
 	videobuf_queue_unlock(q);
 }

 static const struct vm_operations_struct videobuf_vm_ops = {
 	.open	= videobuf_vm_open,
 	.close	= videobuf_vm_close,
 };

 /**
  * videobuf_dma_contig_user_put() - reset pointer to user space buffer
  * @mem: per-buffer private videobuf-dma-contig data
  *
  * This function resets the user space pointer
  */
 static void videobuf_dma_contig_user_put(struct videobuf_dma_contig_memory *mem)
 {
 	mem->dma_handle = 0;
 	mem->size = 0;
 }

 /**
  * videobuf_dma_contig_user_get() - setup user space memory pointer
  * @mem: per-buffer private videobuf-dma-contig data
  * @vb: video buffer to map
  *
  * This function validates and sets up a pointer to user space memory.
  * Only physically contiguous pfn-mapped memory is accepted.
  *
  * Returns 0 if successful.
  */
 static int videobuf_dma_contig_user_get(struct videobuf_dma_contig_memory *mem,
 					struct videobuf_buffer *vb)
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
 	unsigned long prev_pfn, this_pfn;
 	unsigned long pages_done, user_address;
 	unsigned int offset;
 	int ret;

 	offset = vb->baddr & ~PAGE_MASK;
 	mem->size = PAGE_ALIGN(vb->size + offset);
 	ret = -EINVAL;

 	down_read(&mm->mmap_sem);

 	vma = find_vma(mm, vb->baddr);
 	if (!vma)
 		goto out_up;

 	if ((vb->baddr + mem->size) > vma->vm_end)
 		goto out_up;

 	pages_done = 0;
 	prev_pfn = 0; /* kill warning */
 	user_address = vb->baddr;

 	while (pages_done < (mem->size >> PAGE_SHIFT)) {
 		ret = follow_pfn(vma, user_address, &this_pfn);
 		if (ret)
 			break;

 		if (pages_done == 0)
 			mem->dma_handle = (this_pfn << PAGE_SHIFT) + offset;
 		else if (this_pfn != (prev_pfn + 1))
 			ret = -EFAULT;

 		if (ret)
 			break;

 		prev_pfn = this_pfn;
 		user_address += PAGE_SIZE;
 		pages_done++;
 	}

 out_up:
 	up_read(&current->mm->mmap_sem);

 	return ret;
 }

 static struct videobuf_buffer *__videobuf_alloc(size_t size)
 {
 	struct videobuf_dma_contig_memory *mem;
 	struct videobuf_buffer *vb;

 	vb = kzalloc(size + sizeof(*mem), GFP_KERNEL);
 	if (vb) {
 		vb->priv = ((char *)vb) + size;
 		mem = vb->priv;
 		mem->magic = MAGIC_DC_MEM;
 	}

 	return vb;
 }

 static void *__videobuf_to_vaddr(struct videobuf_buffer *buf)
 {
 	struct videobuf_dma_contig_memory *mem = buf->priv;

 	BUG_ON(!mem);
 	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

 	return mem->vaddr;
 }

 static int __videobuf_iolock(struct videobuf_queue *q,
 			     struct videobuf_buffer *vb,
 			     struct v4l2_framebuffer *fbuf)
 {
 	struct videobuf_dma_contig_memory *mem = vb->priv;

 	BUG_ON(!mem);
 	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

 	switch (vb->memory) {
 	case V4L2_MEMORY_MMAP:
 		dev_dbg(q->dev, "%s memory method MMAP\n", __func__);

 		/* All handling should be done by __videobuf_mmap_mapper() */
 		if (!mem->vaddr) {
 			dev_err(q->dev, "memory is not alloced/mmapped.\n");
 			return -EINVAL;
 		}
 		break;
 	case V4L2_MEMORY_USERPTR:
 		dev_dbg(q->dev, "%s memory method USERPTR\n", __func__);

 		/* handle pointer from user space */
 		if (vb->baddr)
 			return videobuf_dma_contig_user_get(mem, vb);

 		/* allocate memory for the read() method */
 		if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(vb->size),
 					GFP_KERNEL))
 			return -ENOMEM;
 		break;
 	case V4L2_MEMORY_OVERLAY:
 	default:
 		dev_dbg(q->dev, "%s memory method OVERLAY/unknown\n", __func__);
 		return -EINVAL;
 	}

 	return 0;
 }

 static int __videobuf_mmap_mapper(struct videobuf_queue *q,
 				  struct videobuf_buffer *buf,
 				  struct vm_area_struct *vma)
 {
 	struct videobuf_dma_contig_memory *mem;
 	struct videobuf_mapping *map;
 	int retval;
 	unsigned long size;

 	dev_dbg(q->dev, "%s\n", __func__);

 	/* create mapping + update buffer list */
 	map = kzalloc(sizeof(struct videobuf_mapping), GFP_KERNEL);
 	if (!map)
 		return -ENOMEM;

 	buf->map = map;
 	map->q = q;

 	buf->baddr = vma->vm_start;

 	mem = buf->priv;
 	BUG_ON(!mem);
 	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

 	if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(buf->bsize),
 				GFP_KERNEL | __GFP_COMP))
 		goto error;

 	/* Try to remap memory */
 	size = vma->vm_end - vma->vm_start;
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	retval = vm_iomap_memory(vma, vma->vm_start, size);
 	if (retval) {
 		dev_err(q->dev, "mmap: remap failed with error %d. ",
 			retval);
 		dma_free_coherent(q->dev, mem->size,
 				  mem->vaddr, mem->dma_handle);
 		goto error;
 	}

 	vma->vm_ops = &videobuf_vm_ops;
 	vma->vm_flags |= VM_DONTEXPAND;
 	vma->vm_private_data = map;

 	dev_dbg(q->dev, "mmap %p: q=%p %08lx-%08lx (%lx) pgoff %08lx buf %d\n",
 		map, q, vma->vm_start, vma->vm_end,
 		(long int)buf->bsize, vma->vm_pgoff, buf->i);

 	videobuf_vm_open(vma);

 	return 0;

 error:
 	kfree(map);
 	return -ENOMEM;
 }

 static struct videobuf_qtype_ops qops = {
 	.magic		= MAGIC_QTYPE_OPS,
 	.alloc_vb	= __videobuf_alloc,
 	.iolock		= __videobuf_iolock,
 	.mmap_mapper	= __videobuf_mmap_mapper,
 	.vaddr		= __videobuf_to_vaddr,
 };

 void videobuf_queue_dma_contig_init(struct videobuf_queue *q,
 				    const struct videobuf_queue_ops *ops,
 				    struct device *dev,
 				    spinlock_t *irqlock,
 				    enum v4l2_buf_type type,
 				    enum v4l2_field field,
 				    unsigned int msize,
 				    void *priv,
 				    struct mutex *ext_lock)
 {
 	videobuf_queue_core_init(q, ops, dev, irqlock, type, field, msize,
 				 priv, &qops, ext_lock);
 }
 EXPORT_SYMBOL_GPL(videobuf_queue_dma_contig_init);

 dma_addr_t videobuf_to_dma_contig(struct videobuf_buffer *buf)
 {
 	struct videobuf_dma_contig_memory *mem = buf->priv;

 	BUG_ON(!mem);
 	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

 	return mem->dma_handle;
 }
 EXPORT_SYMBOL_GPL(videobuf_to_dma_contig);

 void videobuf_dma_contig_free(struct videobuf_queue *q,
 			      struct videobuf_buffer *buf)
 {
 	struct videobuf_dma_contig_memory *mem = buf->priv;

 	/* mmapped memory can't be freed here, otherwise mmapped region
 	   would be released, while still needed. In this case, the memory
 	   release should happen inside videobuf_vm_close().
 	   So, it should free memory only if the memory were allocated for
 	   read() operation.
 	 */
 	if (buf->memory != V4L2_MEMORY_USERPTR)
 		return;

 	if (!mem)
 		return;

 	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

 	/* handle user space pointer case */
 	if (buf->baddr) {
 		videobuf_dma_contig_user_put(mem);
 		return;
 	}

 	/* read() method */
 	if (mem->vaddr) {
 		__videobuf_dc_free(q->dev, mem);
 		mem->vaddr = NULL;
 	}
 }
 EXPORT_SYMBOL_GPL(videobuf_dma_contig_free);

 MODULE_DESCRIPTION("helper module to manage video4linux dma contig buffers");
 MODULE_AUTHOR("Magnus Damm");
 MODULE_LICENSE("GPL");
	/*
	* helper functions for physically contiguous capture buffers
	*
	* The functions support hardware lacking scatter gather support
	* (i.e. the buffers must be linear in physical memory)
	*
	* Copyright (c) 2008 Magnus Damm
	*
	* Based on videobuf-vmalloc.c,
	* (c) 2007 Mauro Carvalho Chehab, <mchehab@infradead.org>
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2
	*/

	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/mm.h>
	#include <linux/pagemap.h>
	#include <linux/dma-mapping.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <media/videobuf-dma-contig.h>

	struct videobuf_dma_contig_memory {
	u32 magic;
	void *vaddr;
	dma_addr_t dma_handle;
	unsigned long size;
	};

	#define MAGIC_DC_MEM 0x0733ac61
	#define MAGIC_CHECK(is, should) \
	if (unlikely((is) != (should))) { \
	pr_err("magic mismatch: %x expected %x\n", (is), (should)); \
	BUG(); \
	}

	static int __videobuf_dc_alloc(struct device *dev,
	struct videobuf_dma_contig_memory *mem,
	unsigned long size, gfp_t flags)
	{
	mem->size = size;
	mem->vaddr = dma_alloc_coherent(dev, mem->size,
	&mem->dma_handle, flags);

	if (!mem->vaddr) {
	dev_err(dev, "memory alloc size %ld failed\n", mem->size);
	return -ENOMEM;
	}

	dev_dbg(dev, "dma mapped data is at %p (%ld)\n", mem->vaddr, mem->size);

	return 0;
	}

	static void __videobuf_dc_free(struct device *dev,
	struct videobuf_dma_contig_memory *mem)
	{
	dma_free_coherent(dev, mem->size, mem->vaddr, mem->dma_handle);

	mem->vaddr = NULL;
	}

	static void videobuf_vm_open(struct vm_area_struct *vma)
	{
	struct videobuf_mapping *map = vma->vm_private_data;
	struct videobuf_queue *q = map->q;

	dev_dbg(q->dev, "vm_open %p [count=%u,vma=%08lx-%08lx]\n",
	map, map->count, vma->vm_start, vma->vm_end);

	videobuf_queue_lock(q);
	map->count++;
	videobuf_queue_unlock(q);
	}

	static void videobuf_vm_close(struct vm_area_struct *vma)
	{
	struct videobuf_mapping *map = vma->vm_private_data;
	struct videobuf_queue *q = map->q;
	int i;

	dev_dbg(q->dev, "vm_close %p [count=%u,vma=%08lx-%08lx]\n",
	map, map->count, vma->vm_start, vma->vm_end);

	videobuf_queue_lock(q);
	if (!--map->count) {
	struct videobuf_dma_contig_memory *mem;

	dev_dbg(q->dev, "munmap %p q=%p\n", map, q);

	/* We need first to cancel streams, before unmapping */
	if (q->streaming)
	videobuf_queue_cancel(q);

	for (i = 0; i < VIDEO_MAX_FRAME; i++) {
	if (NULL == q->bufs[i])
	continue;

	if (q->bufs[i]->map != map)
	continue;

	mem = q->bufs[i]->priv;
	if (mem) {
	/* This callback is called only if kernel has
	allocated memory and this memory is mmapped.
	In this case, memory should be freed,
	in order to do memory unmap.
	*/

	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

	/* vfree is not atomic - can't be
	called with IRQ's disabled
	*/
	dev_dbg(q->dev, "buf[%d] freeing %p\n",
	i, mem->vaddr);

	__videobuf_dc_free(q->dev, mem);
	mem->vaddr = NULL;
	}

	q->bufs[i]->map = NULL;
	q->bufs[i]->baddr = 0;
	}

	kfree(map);

	}
	videobuf_queue_unlock(q);
	}

	static const struct vm_operations_struct videobuf_vm_ops = {
	.open = videobuf_vm_open,
	.close = videobuf_vm_close,
	};

	/**
	* videobuf_dma_contig_user_put() - reset pointer to user space buffer
	* @mem: per-buffer private videobuf-dma-contig data
	*
	* This function resets the user space pointer
	*/
	static void videobuf_dma_contig_user_put(struct videobuf_dma_contig_memory *mem)
	{
	mem->dma_handle = 0;
	mem->size = 0;
	}

	/**
	* videobuf_dma_contig_user_get() - setup user space memory pointer
	* @mem: per-buffer private videobuf-dma-contig data
	* @vb: video buffer to map
	*
	* This function validates and sets up a pointer to user space memory.
	* Only physically contiguous pfn-mapped memory is accepted.
	*
	* Returns 0 if successful.
	*/
	static int videobuf_dma_contig_user_get(struct videobuf_dma_contig_memory *mem,
	struct videobuf_buffer *vb)
	{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma;
	unsigned long prev_pfn, this_pfn;
	unsigned long pages_done, user_address;
	unsigned int offset;
	int ret;

	offset = vb->baddr & ~PAGE_MASK;
	mem->size = PAGE_ALIGN(vb->size + offset);
	ret = -EINVAL;

	down_read(&mm->mmap_sem);

	vma = find_vma(mm, vb->baddr);
	if (!vma)
	goto out_up;

	if ((vb->baddr + mem->size) > vma->vm_end)
	goto out_up;

	pages_done = 0;
	prev_pfn = 0; /* kill warning */
	user_address = vb->baddr;

	while (pages_done < (mem->size >> PAGE_SHIFT)) {
	ret = follow_pfn(vma, user_address, &this_pfn);
	if (ret)
	break;

	if (pages_done == 0)
	mem->dma_handle = (this_pfn << PAGE_SHIFT) + offset;
	else if (this_pfn != (prev_pfn + 1))
	ret = -EFAULT;

	if (ret)
	break;

	prev_pfn = this_pfn;
	user_address += PAGE_SIZE;
	pages_done++;
	}

	out_up:
	up_read(&current->mm->mmap_sem);

	return ret;
	}

	static struct videobuf_buffer *__videobuf_alloc(size_t size)
	{
	struct videobuf_dma_contig_memory *mem;
	struct videobuf_buffer *vb;

	vb = kzalloc(size + sizeof(*mem), GFP_KERNEL);
	if (vb) {
	vb->priv = ((char *)vb) + size;
	mem = vb->priv;
	mem->magic = MAGIC_DC_MEM;
	}

	return vb;
	}

	static void __videobuf_to_vaddr(struct videobuf_buffer buf)
	{
	struct videobuf_dma_contig_memory *mem = buf->priv;

	BUG_ON(!mem);
	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

	return mem->vaddr;
	}

	static int __videobuf_iolock(struct videobuf_queue *q,
	struct videobuf_buffer *vb,
	struct v4l2_framebuffer *fbuf)
	{
	struct videobuf_dma_contig_memory *mem = vb->priv;

	BUG_ON(!mem);
	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

	switch (vb->memory) {
	case V4L2_MEMORY_MMAP:
	dev_dbg(q->dev, "%s memory method MMAP\n", __func__);

	/* All handling should be done by __videobuf_mmap_mapper() */
	if (!mem->vaddr) {
	dev_err(q->dev, "memory is not alloced/mmapped.\n");
	return -EINVAL;
	}
	break;
	case V4L2_MEMORY_USERPTR:
	dev_dbg(q->dev, "%s memory method USERPTR\n", __func__);

	/* handle pointer from user space */
	if (vb->baddr)
	return videobuf_dma_contig_user_get(mem, vb);

	/* allocate memory for the read() method */
	if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(vb->size),
	GFP_KERNEL))
	return -ENOMEM;
	break;
	case V4L2_MEMORY_OVERLAY:
	default:
	dev_dbg(q->dev, "%s memory method OVERLAY/unknown\n", __func__);
	return -EINVAL;
	}

	return 0;
	}

	static int __videobuf_mmap_mapper(struct videobuf_queue *q,
	struct videobuf_buffer *buf,
	struct vm_area_struct *vma)
	{
	struct videobuf_dma_contig_memory *mem;
	struct videobuf_mapping *map;
	int retval;
	unsigned long size;

	dev_dbg(q->dev, "%s\n", __func__);

	/* create mapping + update buffer list */
	map = kzalloc(sizeof(struct videobuf_mapping), GFP_KERNEL);
	if (!map)
	return -ENOMEM;

	buf->map = map;
	map->q = q;

	buf->baddr = vma->vm_start;

	mem = buf->priv;
	BUG_ON(!mem);
	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

	if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(buf->bsize),
	GFP_KERNEL \| __GFP_COMP))
	goto error;

	/* Try to remap memory */
	size = vma->vm_end - vma->vm_start;
	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
	retval = vm_iomap_memory(vma, vma->vm_start, size);
	if (retval) {
	dev_err(q->dev, "mmap: remap failed with error %d. ",
	retval);
	dma_free_coherent(q->dev, mem->size,
	mem->vaddr, mem->dma_handle);
	goto error;
	}

	vma->vm_ops = &videobuf_vm_ops;
	vma->vm_flags \|= VM_DONTEXPAND;
	vma->vm_private_data = map;

	dev_dbg(q->dev, "mmap %p: q=%p %08lx-%08lx (%lx) pgoff %08lx buf %d\n",
	map, q, vma->vm_start, vma->vm_end,
	(long int)buf->bsize, vma->vm_pgoff, buf->i);

	videobuf_vm_open(vma);

	return 0;

	error:
	kfree(map);
	return -ENOMEM;
	}

	static struct videobuf_qtype_ops qops = {
	.magic = MAGIC_QTYPE_OPS,
	.alloc_vb = __videobuf_alloc,
	.iolock = __videobuf_iolock,
	.mmap_mapper = __videobuf_mmap_mapper,
	.vaddr = __videobuf_to_vaddr,
	};

	void videobuf_queue_dma_contig_init(struct videobuf_queue *q,
	const struct videobuf_queue_ops *ops,
	struct device *dev,
	spinlock_t *irqlock,
	enum v4l2_buf_type type,
	enum v4l2_field field,
	unsigned int msize,
	void *priv,
	struct mutex *ext_lock)
	{
	videobuf_queue_core_init(q, ops, dev, irqlock, type, field, msize,
	priv, &qops, ext_lock);
	}
	EXPORT_SYMBOL_GPL(videobuf_queue_dma_contig_init);

	dma_addr_t videobuf_to_dma_contig(struct videobuf_buffer *buf)
	{
	struct videobuf_dma_contig_memory *mem = buf->priv;

	BUG_ON(!mem);
	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

	return mem->dma_handle;
	}
	EXPORT_SYMBOL_GPL(videobuf_to_dma_contig);

	void videobuf_dma_contig_free(struct videobuf_queue *q,
	struct videobuf_buffer *buf)
	{
	struct videobuf_dma_contig_memory *mem = buf->priv;

	/* mmapped memory can't be freed here, otherwise mmapped region
	would be released, while still needed. In this case, the memory
	release should happen inside videobuf_vm_close().
	So, it should free memory only if the memory were allocated for
	read() operation.
	*/
	if (buf->memory != V4L2_MEMORY_USERPTR)
	return;

	if (!mem)
	return;

	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);

	/* handle user space pointer case */
	if (buf->baddr) {
	videobuf_dma_contig_user_put(mem);
	return;
	}

	/* read() method */
	if (mem->vaddr) {
	__videobuf_dc_free(q->dev, mem);
	mem->vaddr = NULL;
	}
	}
	EXPORT_SYMBOL_GPL(videobuf_dma_contig_free);

	MODULE_DESCRIPTION("helper module to manage video4linux dma contig buffers");
	MODULE_AUTHOR("Magnus Damm");
	MODULE_LICENSE("GPL");