Re: [PATCH 08/10] v4l: vb2-dma-contig: code refactoring, support for DMABUF exporting

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 23-01-2012 11:51, Tomasz Stanislawski escreveu:
> Signed-off-by: Pawel Osciak <pawel@osciak.com>
> 	[author of the original file]
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> 	[implemetation of mmap, finish/prepare]
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
> 	[implementation of userprt handling]
> Signed-off-by: Sumit Semwal <sumit.semwal@ti.com>
> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
> 	[PoC for importing dmabuf buffer]
> Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
>        [buffer exporting using dmabuf, code refactoring]
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

Please provide a diff against the existing driver, in order to allow reviewing
what has changed.

> ---
>  drivers/media/video/videobuf2-dma-contig.c |  762 ++++++++++++++++++++++++++++
>  1 files changed, 762 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/media/video/videobuf2-dma-contig.c
> 
> diff --git a/drivers/media/video/videobuf2-dma-contig.c b/drivers/media/video/videobuf2-dma-contig.c
> new file mode 100644
> index 0000000..d95b23a
> --- /dev/null
> +++ b/drivers/media/video/videobuf2-dma-contig.c
> @@ -0,0 +1,762 @@
> +/*
> + * videobuf2-dma-contig.c - DMA contig memory allocator for videobuf2
> + *
> + * Copyright (C) 2010 Samsung Electronics
> + *
> + * Author: Pawel Osciak <pawel@osciak.com>
> + *
> + * 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.
> + */
> +
> +#include <linux/dma-buf.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/module.h>
> +#include <linux/scatterlist.h>
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +
> +#include <media/videobuf2-core.h>
> +#include <media/videobuf2-memops.h>
> +
> +struct vb2_dc_buf {
> +	struct device			*dev;
> +	void				*vaddr;
> +	unsigned long			size;
> +	dma_addr_t			dma_addr;
> +	struct sg_table			*dma_sgt;
> +	enum dma_data_direction		dma_dir;
> +
> +	/* MMAP related */
> +	struct vb2_vmarea_handler	handler;
> +	atomic_t			refcount;
> +	struct dma_buf			*dma_buf;
> +	struct sg_table			*sgt_base;
> +
> +	/* USERPTR related */
> +	struct vm_area_struct		*vma;
> +
> +	/* DMABUF related */
> +	struct dma_buf_attachment	*db_attach;
> +};
> +
> +/*********************************************/
> +/*        scatterlist table functions        */
> +/*********************************************/
> +
> +static struct sg_table *vb2_dc_pages_to_sgt(struct page **pages,
> +	unsigned long n_pages, size_t offset, size_t offset2)
> +{
> +	struct sg_table *sgt;
> +	int i, j; /* loop counters */
> +	int cur_page, chunks;
> +	int ret;
> +	struct scatterlist *s;
> +
> +	sgt = kzalloc(sizeof *sgt, GFP_KERNEL);
> +	if (!sgt)
> +		return ERR_PTR(-ENOMEM);
> +
> +	/* compute number of chunks */
> +	chunks = 1;
> +	for (i = 1; i < n_pages; ++i)
> +		if (pages[i] != pages[i - 1] + 1)
> +			++chunks;
> +
> +	ret = sg_alloc_table(sgt, chunks, GFP_KERNEL);
> +	if (ret) {
> +		kfree(sgt);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	/* merging chunks and putting them into the scatterlist */
> +	cur_page = 0;
> +	for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
> +		size_t size = PAGE_SIZE;
> +
> +		for (j = cur_page + 1; j < n_pages; ++j) {
> +			if (pages[j] != pages[j - 1] + 1)
> +				break;
> +			size += PAGE_SIZE;
> +		}
> +
> +		/* cut offset if chunk starts at the first page */
> +		if (cur_page == 0)
> +			size -= offset;
> +		/* cut offset2 if chunk ends at the last page */
> +		if (j == n_pages)
> +			size -= offset2;
> +
> +		sg_set_page(s, pages[cur_page], size, offset);
> +		offset = 0;
> +		cur_page = j;
> +	}
> +
> +	return sgt;
> +}
> +
> +static void vb2_dc_release_sgtable(struct sg_table *sgt)
> +{
> +	sg_free_table(sgt);
> +	kfree(sgt);
> +}
> +
> +static void vb2_dc_put_sgtable(struct sg_table *sgt, int dirty)
> +{
> +	struct scatterlist *s;
> +	int i, j;
> +
> +	for_each_sg(sgt->sgl, s, sgt->nents, i) {
> +		struct page *page = sg_page(s);
> +		int n_pages = PAGE_ALIGN(s->offset + s->length) >> PAGE_SHIFT;
> +
> +		for (j = 0; j < n_pages; ++j, ++page) {
> +			if (dirty)
> +				set_page_dirty_lock(page);
> +			put_page(page);
> +		}
> +	}
> +
> +	vb2_dc_release_sgtable(sgt);
> +}
> +
> +static unsigned long vb2_dc_get_contiguous_size(struct sg_table *sgt)
> +{
> +	struct scatterlist *s;
> +	dma_addr_t expected = sg_dma_address(sgt->sgl);
> +	int i;
> +	unsigned long size = 0;
> +
> +	for_each_sg(sgt->sgl, s, sgt->nents, i) {
> +		if (sg_dma_address(s) != expected)
> +			break;
> +		expected = sg_dma_address(s) + sg_dma_len(s);
> +		size += sg_dma_len(s);
> +	}
> +	return size;
> +}
> +
> +/*********************************************/
> +/*         callbacks for all buffers         */
> +/*********************************************/
> +
> +static void *vb2_dc_cookie(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +
> +	return &buf->dma_addr;
> +}
> +
> +static void *vb2_dc_vaddr(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +
> +	return buf->vaddr;
> +}
> +
> +static unsigned int vb2_dc_num_users(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +
> +	return atomic_read(&buf->refcount);
> +}
> +
> +static void vb2_dc_prepare(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	if (!sgt)
> +		return;
> +
> +	dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> +}
> +
> +static void vb2_dc_finish(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	if (!sgt)
> +		return;
> +
> +	dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> +}
> +
> +/*********************************************/
> +/*        callbacks for MMAP buffers         */
> +/*********************************************/
> +
> +static void vb2_dc_put(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +
> +	if (!atomic_dec_and_test(&buf->refcount))
> +		return;
> +
> +	if (buf->dma_buf)
> +		dma_buf_put(buf->dma_buf);
> +	vb2_dc_release_sgtable(buf->sgt_base);
> +	dma_free_coherent(buf->dev, buf->size, buf->vaddr,
> +		buf->dma_addr);
> +	kfree(buf);
> +}
> +
> +static void *vb2_dc_alloc(void *alloc_ctx, unsigned long size)
> +{
> +	struct device *dev = alloc_ctx;
> +	struct vb2_dc_buf *buf;
> +	int ret;
> +	int n_pages;
> +	struct page **pages = NULL;
> +
> +	buf = kzalloc(sizeof *buf, GFP_KERNEL);
> +	if (!buf)
> +		return ERR_PTR(-ENOMEM);
> +
> +	buf->dev = dev;
> +	buf->size = size;
> +	buf->vaddr = dma_alloc_coherent(buf->dev, buf->size, &buf->dma_addr,
> +		GFP_KERNEL);
> +
> +	ret = -ENOMEM;
> +	if (!buf->vaddr) {
> +		dev_err(dev, "dma_alloc_coherent of size %ld failed\n",
> +			size);
> +		goto fail_buf;
> +	}
> +
> +	WARN_ON((unsigned long)buf->vaddr & ~PAGE_MASK);
> +	WARN_ON(buf->dma_addr & ~PAGE_MASK);
> +
> +	n_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +
> +	pages = kmalloc(n_pages * sizeof pages[0], GFP_KERNEL);
> +	if (!pages) {
> +		printk(KERN_ERR "failed to alloc page table\n");
> +		goto fail_dma;
> +	}
> +
> +	ret = dma_get_pages(dev, buf->vaddr, buf->dma_addr, pages, n_pages);
> +	if (ret < 0) {
> +		printk(KERN_ERR "failed to get buffer pages from DMA API\n");
> +		goto fail_pages;
> +	}
> +	if (ret != n_pages) {
> +		ret = -EFAULT;
> +		printk(KERN_ERR "failed to get all pages from DMA API\n");
> +		goto fail_pages;
> +	}
> +
> +	buf->sgt_base = vb2_dc_pages_to_sgt(pages, n_pages, 0, 0);
> +	if (IS_ERR(buf->sgt_base)) {
> +		ret = PTR_ERR(buf->sgt_base);
> +		printk(KERN_ERR "failed to prepare sg table\n");
> +		goto fail_pages;
> +	}
> +
> +	/* pages are no longer needed */
> +	kfree(pages);
> +
> +	buf->handler.refcount = &buf->refcount;
> +	buf->handler.put = vb2_dc_put;
> +	buf->handler.arg = buf;
> +
> +	atomic_inc(&buf->refcount);
> +
> +	return buf;
> +
> +fail_pages:
> +	kfree(pages);
> +
> +fail_dma:
> +	dma_free_coherent(buf->dev, buf->size, buf->vaddr, buf->dma_addr);
> +
> +fail_buf:
> +	kfree(buf);
> +
> +	return ERR_PTR(ret);
> +}
> +
> +static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +	int ret;
> +
> +	/*
> +	 * dma_mmap_* uses vm_pgoff as in-buffer offset, but we want to
> +	 * map whole buffer
> +	 */
> +	vma->vm_pgoff = 0;
> +
> +	ret = dma_mmap_writecombine(buf->dev, vma, buf->vaddr,
> +		buf->dma_addr, buf->size);
> +
> +	if (ret) {
> +		printk(KERN_ERR "Remapping memory failed, error: %d\n", ret);
> +		return ret;
> +	}
> +
> +	vma->vm_flags		|= VM_DONTEXPAND | VM_RESERVED;
> +	vma->vm_private_data	= &buf->handler;
> +	vma->vm_ops		= &vb2_common_vm_ops;
> +
> +	vma->vm_ops->open(vma);
> +
> +	printk(KERN_DEBUG "%s: mapped dma addr 0x%08lx at 0x%08lx, size %ld\n",
> +		__func__, (unsigned long)buf->dma_addr, vma->vm_start,
> +		buf->size);
> +
> +	return 0;
> +}
> +
> +/*********************************************/
> +/*         DMABUF ops for exporters          */
> +/*********************************************/
> +
> +struct vb2_dc_attachment {
> +	struct sg_table sgt;
> +	enum dma_data_direction dir;
> +};
> +
> +static int vb2_dc_dmabuf_ops_attach(struct dma_buf *dbuf, struct device *dev,
> +	struct dma_buf_attachment *dbuf_attach)
> +{
> +	/* nothing to be done */
> +	return 0;
> +}
> +
> +static void vb2_dc_dmabuf_ops_detach(struct dma_buf *dbuf,
> +	struct dma_buf_attachment *db_attach)
> +{
> +	struct vb2_dc_attachment *attach = db_attach->priv;
> +	struct sg_table *sgt;
> +
> +	if (!attach)
> +		return;
> +
> +	sgt = &attach->sgt;
> +
> +	dma_unmap_sg(db_attach->dev, sgt->sgl, sgt->nents, attach->dir);
> +	sg_free_table(sgt);
> +	kfree(attach);
> +	db_attach->priv = NULL;
> +}
> +
> +static struct sg_table *vb2_dc_dmabuf_ops_map(
> +	struct dma_buf_attachment *db_attach, enum dma_data_direction dir)
> +{
> +	struct dma_buf *dbuf = db_attach->dmabuf;
> +	struct vb2_dc_buf *buf = dbuf->priv;
> +	struct vb2_dc_attachment *attach = db_attach->priv;
> +	struct sg_table *sgt;
> +	struct scatterlist *rd, *wr;
> +	int i, ret;
> +
> +	/* return previously mapped sg table */
> +	if (attach)
> +		return &attach->sgt;
> +
> +	attach = kzalloc(sizeof *attach, GFP_KERNEL);
> +	if (!attach)
> +		return ERR_PTR(-ENOMEM);
> +
> +	sgt = &attach->sgt;
> +	attach->dir = dir;
> +
> +	/* copying the buf->base_sgt to attachment */
> +	ret = sg_alloc_table(sgt, buf->sgt_base->orig_nents, GFP_KERNEL);
> +	if (ret) {
> +		kfree(attach);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	rd = buf->sgt_base->sgl;
> +	wr = sgt->sgl;
> +	for (i = 0; i < sgt->orig_nents; ++i) {
> +		sg_set_page(wr, sg_page(rd), rd->length, rd->offset);
> +		rd = sg_next(rd);
> +		wr = sg_next(wr);
> +	}
> +
> +	/* mapping new sglist to the client */
> +	ret = dma_map_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, dir);
> +	if (ret <= 0) {
> +		printk(KERN_ERR "failed to map scatterlist\n");
> +		sg_free_table(sgt);
> +		kfree(attach);
> +		return ERR_PTR(-EIO);
> +	}
> +
> +	db_attach->priv = attach;
> +
> +	return sgt;
> +}
> +
> +static void vb2_dc_dmabuf_ops_unmap(struct dma_buf_attachment *db_attach,
> +	struct sg_table *sgt)
> +{
> +	/* nothing to be done here */
> +}
> +
> +static void vb2_dc_dmabuf_ops_release(struct dma_buf *dbuf)
> +{
> +	/* drop reference obtained in vb2_dc_get_dmabuf */
> +	vb2_dc_put(dbuf->priv);
> +}
> +
> +static struct dma_buf_ops vb2_dc_dmabuf_ops = {
> +	.attach = vb2_dc_dmabuf_ops_attach,
> +	.detach = vb2_dc_dmabuf_ops_detach,
> +	.map_dma_buf = vb2_dc_dmabuf_ops_map,
> +	.unmap_dma_buf = vb2_dc_dmabuf_ops_unmap,
> +	.release = vb2_dc_dmabuf_ops_release,
> +};
> +
> +static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +	struct dma_buf *dbuf;
> +
> +	if (buf->dma_buf)
> +		return buf->dma_buf;
> +
> +	/* dmabuf keeps reference to vb2 buffer */
> +	atomic_inc(&buf->refcount);
> +	dbuf = dma_buf_export(buf, &vb2_dc_dmabuf_ops, buf->size, 0);
> +	if (IS_ERR(dbuf)) {
> +		atomic_dec(&buf->refcount);
> +		return NULL;
> +	}
> +
> +	buf->dma_buf = dbuf;
> +
> +	return dbuf;
> +}
> +
> +/*********************************************/
> +/*       callbacks for USERPTR buffers       */
> +/*********************************************/
> +
> +static inline int vma_is_io(struct vm_area_struct *vma)
> +{
> +	return !!(vma->vm_flags & (VM_IO | VM_PFNMAP));
> +}
> +
> +static int vb2_dc_get_pages(unsigned long start, struct page **pages,
> +	int n_pages, struct vm_area_struct **copy_vma, int write)
> +{
> +	struct vm_area_struct *vma;
> +	int n = 0; /* number of get pages */
> +	int ret = -EFAULT;
> +
> +	/* entering critical section for mm access */
> +	down_read(&current->mm->mmap_sem);
> +
> +	vma = find_vma(current->mm, start);
> +	if (!vma) {
> +		printk(KERN_ERR "no vma for address %lu\n", start);
> +		goto cleanup;
> +	}
> +
> +	if (vma_is_io(vma)) {
> +		unsigned long pfn;
> +
> +		if (vma->vm_end - start < n_pages * PAGE_SIZE) {
> +			printk(KERN_ERR "vma is too small\n");
> +			goto cleanup;
> +		}
> +
> +		for (n = 0; n < n_pages; ++n, start += PAGE_SIZE) {
> +			ret = follow_pfn(vma, start, &pfn);
> +			if (ret) {
> +				printk(KERN_ERR "no page for address %lu\n",
> +					start);
> +				goto cleanup;
> +			}
> +			pages[n] = pfn_to_page(pfn);
> +			get_page(pages[n]);
> +		}
> +	} else {
> +		n = get_user_pages(current, current->mm, start & PAGE_MASK,
> +			n_pages, write, 1, pages, NULL);
> +		if (n != n_pages) {
> +			printk(KERN_ERR "got only %d of %d user pages\n",
> +				n, n_pages);
> +			goto cleanup;
> +		}
> +	}
> +
> +	*copy_vma = vb2_get_vma(vma);
> +	if (!*copy_vma) {
> +		printk(KERN_ERR "failed to copy vma\n");
> +		ret = -ENOMEM;
> +		goto cleanup;
> +	}
> +
> +	/* leaving critical section for mm access */
> +	up_read(&current->mm->mmap_sem);
> +
> +	return 0;
> +
> +cleanup:
> +	up_read(&current->mm->mmap_sem);
> +
> +	/* putting user pages if used, can be done wothout the lock */
> +	while (n)
> +		put_page(pages[--n]);
> +
> +	return ret;
> +}
> +
> +static void vb2_dc_put_userptr(void *buf_priv)
> +{
> +	struct vb2_dc_buf *buf = buf_priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	dma_unmap_sg(buf->dev, sgt->sgl, sgt->orig_nents, buf->dma_dir);
> +	vb2_dc_put_sgtable(sgt, !vma_is_io(buf->vma));
> +	vb2_put_vma(buf->vma);
> +	kfree(buf);
> +}
> +
> +static void *vb2_dc_get_userptr(void *alloc_ctx, unsigned long vaddr,
> +	unsigned long size, int write)
> +{
> +	struct vb2_dc_buf *buf;
> +	unsigned long start, end, offset, offset2;
> +	struct page **pages;
> +	int n_pages;
> +	int ret = 0;
> +	struct sg_table *sgt;
> +	unsigned long contig_size;
> +
> +	buf = kzalloc(sizeof *buf, GFP_KERNEL);
> +	if (!buf)
> +		return ERR_PTR(-ENOMEM);
> +
> +	buf->dev = alloc_ctx;
> +	buf->dma_dir = write ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> +
> +	start = (unsigned long)vaddr & PAGE_MASK;
> +	offset = (unsigned long)vaddr & ~PAGE_MASK;
> +	end = PAGE_ALIGN((unsigned long)vaddr + size);
> +	offset2 = end - (unsigned long)vaddr - size;
> +	n_pages = (end - start) >> PAGE_SHIFT;
> +
> +	pages = kmalloc(n_pages * sizeof pages[0], GFP_KERNEL);
> +	if (!pages) {
> +		ret = -ENOMEM;
> +		printk(KERN_ERR "failed to allocate pages table\n");
> +		goto fail_buf;
> +	}
> +
> +	/* extract page list from userspace mapping */
> +	ret = vb2_dc_get_pages(start, pages, n_pages, &buf->vma, write);
> +	if (ret) {
> +		printk(KERN_ERR "failed to get user pages\n");
> +		goto fail_pages;
> +	}
> +
> +	sgt = vb2_dc_pages_to_sgt(pages, n_pages, offset, offset2);
> +	if (!sgt) {
> +		printk(KERN_ERR "failed to create scatterlist table\n");
> +		ret = -ENOMEM;
> +		goto fail_get_pages;
> +	}
> +
> +	/* pages are no longer needed */
> +	kfree(pages);
> +	pages = NULL;
> +
> +	sgt->nents = dma_map_sg(buf->dev, sgt->sgl, sgt->orig_nents,
> +		buf->dma_dir);
> +	if (sgt->nents <= 0) {
> +		printk(KERN_ERR "failed to map scatterlist\n");
> +		ret = -EIO;
> +		goto fail_sgt;
> +	}
> +
> +	contig_size = vb2_dc_get_contiguous_size(sgt);
> +	if (contig_size < size) {
> +		printk(KERN_ERR "contiguous mapping is too small %lu/%lu\n",
> +			contig_size, size);
> +		ret = -EFAULT;
> +		goto fail_map_sg;
> +	}
> +
> +	buf->dma_addr = sg_dma_address(sgt->sgl);
> +	buf->size = size;
> +	buf->dma_sgt = sgt;
> +
> +	atomic_inc(&buf->refcount);
> +
> +	return buf;
> +
> +fail_map_sg:
> +	dma_unmap_sg(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> +
> +fail_sgt:
> +	vb2_dc_put_sgtable(sgt, 0);
> +
> +fail_get_pages:
> +	while (pages && n_pages)
> +		put_page(pages[--n_pages]);
> +	vb2_put_vma(buf->vma);
> +
> +fail_pages:
> +	kfree(pages); /* kfree is NULL-proof */
> +
> +fail_buf:
> +	kfree(buf);
> +
> +	return ERR_PTR(ret);
> +}
> +
> +/*********************************************/
> +/*       callbacks for DMABUF buffers        */
> +/*********************************************/
> +
> +static int vb2_dc_map_dmabuf(void *mem_priv)
> +{
> +	struct vb2_dc_buf *buf = mem_priv;
> +	struct sg_table *sgt;
> +	unsigned long contig_size;
> +	int ret = 0;
> +
> +	if (WARN_ON(!buf->db_attach)) {
> +		printk(KERN_ERR "trying to pin a non attached buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	if (WARN_ON(buf->dma_sgt)) {
> +		printk(KERN_ERR "dmabuf buffer is already pinned\n");
> +		return 0;
> +	}
> +
> +	/* get the associated scatterlist for this buffer */
> +	sgt = dma_buf_map_attachment(buf->db_attach, buf->dma_dir);
> +	if (IS_ERR_OR_NULL(sgt)) {
> +		printk(KERN_ERR "Error getting dmabuf scatterlist\n");
> +		return -EINVAL;
> +	}
> +
> +	/* checking if dmabuf is big enough to store contiguous chunk */
> +	contig_size = vb2_dc_get_contiguous_size(sgt);
> +	if (contig_size < buf->size) {
> +		printk(KERN_ERR "contiguous chunk of dmabuf is too small\n");
> +		ret = -EFAULT;
> +		goto fail_map;
> +	}
> +
> +	buf->dma_addr = sg_dma_address(sgt->sgl);
> +	buf->dma_sgt = sgt;
> +
> +	return 0;
> +
> +fail_map:
> +	dma_buf_unmap_attachment(buf->db_attach, sgt);
> +
> +	return ret;
> +}
> +
> +static void vb2_dc_unmap_dmabuf(void *mem_priv)
> +{
> +	struct vb2_dc_buf *buf = mem_priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	if (WARN_ON(!buf->db_attach)) {
> +		printk(KERN_ERR "trying to unpin a not attached buffer\n");
> +		return;
> +	}
> +
> +	if (WARN_ON(!sgt)) {
> +		printk(KERN_ERR "dmabuf buffer is already unpinned\n");
> +		return;
> +	}
> +
> +	dma_buf_unmap_attachment(buf->db_attach, sgt);
> +
> +	buf->dma_addr = 0;
> +	buf->dma_sgt = NULL;
> +}
> +
> +static void vb2_dc_detach_dmabuf(void *mem_priv)
> +{
> +	struct vb2_dc_buf *buf = mem_priv;
> +
> +	if (buf->dma_addr)
> +		vb2_dc_unmap_dmabuf(buf);
> +
> +	/* detach this attachment */
> +	dma_buf_detach(buf->db_attach->dmabuf, buf->db_attach);
> +	kfree(buf);
> +}
> +
> +static void *vb2_dc_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,
> +	unsigned long size, int write)
> +{
> +	struct vb2_dc_buf *buf;
> +	struct dma_buf_attachment *dba;
> +
> +	if (dbuf->size < size)
> +		return ERR_PTR(-EFAULT);
> +
> +	buf = kzalloc(sizeof *buf, GFP_KERNEL);
> +	if (!buf)
> +		return ERR_PTR(-ENOMEM);
> +
> +	buf->dev = alloc_ctx;
> +	/* create attachment for the dmabuf with the user device */
> +	dba = dma_buf_attach(dbuf, buf->dev);
> +	if (IS_ERR(dba)) {
> +		printk(KERN_ERR "failed to attach dmabuf\n");
> +		kfree(buf);
> +		return dba;
> +	}
> +
> +	buf->dma_dir = write ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> +	buf->size = size;
> +	buf->db_attach = dba;
> +
> +	return buf;
> +}
> +
> +/*********************************************/
> +/*       DMA CONTIG exported functions       */
> +/*********************************************/
> +
> +const struct vb2_mem_ops vb2_dma_contig_memops = {
> +	.alloc		= vb2_dc_alloc,
> +	.put		= vb2_dc_put,
> +	.get_dmabuf	= vb2_dc_get_dmabuf,
> +	.cookie		= vb2_dc_cookie,
> +	.vaddr		= vb2_dc_vaddr,
> +	.mmap		= vb2_dc_mmap,
> +	.get_userptr	= vb2_dc_get_userptr,
> +	.put_userptr	= vb2_dc_put_userptr,
> +	.prepare	= vb2_dc_prepare,
> +	.finish		= vb2_dc_finish,
> +	.map_dmabuf	= vb2_dc_map_dmabuf,
> +	.unmap_dmabuf	= vb2_dc_unmap_dmabuf,
> +	.attach_dmabuf	= vb2_dc_attach_dmabuf,
> +	.detach_dmabuf	= vb2_dc_detach_dmabuf,
> +	.num_users	= vb2_dc_num_users,
> +};
> +EXPORT_SYMBOL_GPL(vb2_dma_contig_memops);
> +
> +void *vb2_dma_contig_init_ctx(struct device *dev)
> +{
> +	return dev;
> +}
> +EXPORT_SYMBOL_GPL(vb2_dma_contig_init_ctx);
> +
> +void vb2_dma_contig_cleanup_ctx(void *alloc_ctx)
> +{
> +}
> +EXPORT_SYMBOL_GPL(vb2_dma_contig_cleanup_ctx);
> +
> +MODULE_DESCRIPTION("DMA-contig memory handling routines for videobuf2");
> +MODULE_AUTHOR("Pawel Osciak <pawel@osciak.com>");
> +MODULE_LICENSE("GPL");