[PATCH 08/11] v4l: vb2-dma-contig: add support for scatterlist in userptr mode
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Fri Apr 6 08:02:58 PDT 2012
Hi Tomasz,
On Thursday 05 April 2012 16:00:05 Tomasz Stanislawski wrote:
> From: Andrzej Pietrasiewicz <andrzej.p at samsung.com>
>
> This patch introduces usage of dma_map_sg to map memory behind
> a userspace pointer to a device as dma-contiguous mapping.
>
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p at samsung.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> [bugfixing]
> Signed-off-by: Kamil Debski <k.debski at samsung.com>
> [bugfixing]
> Signed-off-by: Tomasz Stanislawski <t.stanislaws at samsung.com>
> [add sglist subroutines/code refactoring]
> Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
> ---
> drivers/media/video/videobuf2-dma-contig.c | 282 +++++++++++++++++++++++--
> 1 files changed, 265 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/media/video/videobuf2-dma-contig.c
> b/drivers/media/video/videobuf2-dma-contig.c index 476e536..6ab3165 100644
> --- a/drivers/media/video/videobuf2-dma-contig.c
> +++ b/drivers/media/video/videobuf2-dma-contig.c
[snip]
> @@ -32,6 +36,98 @@ struct vb2_dc_buf {
> };
>
> /*********************************************/
> +/* 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)
"offset2" isn't very descriptive. I would replace it with the total size of
the buffer instead (or, alternatively, rename offset to offset_start and
offset2 to offset_end, but I like the first option better).
> +{
> + struct sg_table *sgt;
> + int i, j; /* loop counters */
I don't think the comment is needed.
> + int cur_page, chunks;
i, j, cur_page and chunks can't be negative. Could you please make them
unsigned int (and I would order them) ?
Also, Documentation/CodingStyle favors one variable declaration per line,
without commas for multiple declarations.
> + 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_sgt_foreach_page(struct sg_table *sgt,
> + void (*cb)(struct page *pg))
> +{
> + 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)
> + cb(page);
Same for i, j and n_pages here.
> + }
> +}
> +
> +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;
Same for i here.
> + 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 */
> /*********************************************/
>
> @@ -116,42 +212,194 @@ static int vb2_dc_mmap(void *buf_priv, struct
> vm_area_struct *vma) /* callbacks for USERPTR buffers */
> /*********************************************/
>
> +static inline int vma_is_io(struct vm_area_struct *vma)
> +{
> + return !!(vma->vm_flags & (VM_IO | VM_PFNMAP));
> +}
> +
> +static struct vm_area_struct *vb2_dc_get_user_vma(
> + unsigned long start, unsigned long size)
> +{
> + struct vm_area_struct *vma;
> +
> + /* current->mm->mmap_sem is taken by videobuf2 core */
> + vma = find_vma(current->mm, start);
> + if (!vma) {
> + printk(KERN_ERR "no vma for address %lu\n", start);
> + return ERR_PTR(-EFAULT);
> + }
> +
> + if (vma->vm_end - vma->vm_start < size) {
> + printk(KERN_ERR "vma at %lu is too small for %lu bytes\n",
> + start, size);
> + return ERR_PTR(-EFAULT);
> + }
Should we support multiple VMAs, or do you think that's not worth it ?
> + vma = vb2_get_vma(vma);
> + if (!vma) {
> + printk(KERN_ERR "failed to copy vma\n");
> + return ERR_PTR(-ENOMEM);
> + }
I still think there's no need to copy the VMA. get_user_pages() will make sure
the memory doesn't get paged out, and we don't need to ensure that the
userspace mapping stays in place as our cache operations use a scatter list.
Storing the result of vma_is_io() in vb2_dc_buf should be enough.
> + return vma;
> +}
> +
> +static int vb2_dc_get_user_pages(unsigned long start, struct page **pages,
> + int n_pages, struct vm_area_struct *vma, int write)
> +{
> + int n;
n_pages and n can be unsigned (and I would rename n to i, to be coherent with
the rest of the file).
> +
> + if (vma_is_io(vma)) {
> + for (n = 0; n < n_pages; ++n, start += PAGE_SIZE) {
> + unsigned long pfn;
> + int ret = follow_pfn(vma, start, &pfn);
> +
> + if (ret) {
> + printk(KERN_ERR "no page for address %lu\n",
> + start);
> + return ret;
> + }
> + pages[n] = pfn_to_page(pfn);
> + }
> + } 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);
> + while (n)
> + put_page(pages[--n]);
> + return -EFAULT;
> + }
> + }
> +
> + return 0;
> +}
> +
> +static void vb2_dc_set_page_dirty(struct page *page)
> +{
> + set_page_dirty_lock(page);
> +}
> +
> +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);
> + if (!vma_is_io(buf->vma)) {
> + vb2_dc_sgt_foreach_page(sgt, vb2_dc_set_page_dirty);
> + vb2_dc_sgt_foreach_page(sgt, put_page);
This results in two iterations over the pages. Wouldn't it better to fold the
vb2_dc_sgt_foreach_page() function into this one, and loop once only ?
vb2_dc_sgt_foreach_page() is also called in the cleanup path of
vb2_dc_get_userptr(), but you have the list of pages available in the
function, so you can iterate over it directly.
> + }
> +
> + vb2_dc_release_sgtable(sgt);
> + vb2_put_vma(buf->vma);
> + kfree(buf);
> +}
> +
> static void *vb2_dc_get_userptr(void *alloc_ctx, unsigned long vaddr,
> - unsigned long size, int write)
> + unsigned long size, int write)
> {
> struct vb2_dc_buf *buf;
> - struct vm_area_struct *vma;
> - dma_addr_t dma_addr = 0;
> - int ret;
> + unsigned long start, end, offset, offset2;
If you don't use the buffer size above, please rename offset2 here too (and
avoid multiple variable declarations per line).
> + 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);
>
> - ret = vb2_get_contig_userptr(vaddr, size, &vma, &dma_addr);
> + 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;
vaddr is already an unsigned long, there's no need to cast it.
> + 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;
> + }
> +
> + buf->vma = vb2_dc_get_user_vma(start, end - start);
> + if (IS_ERR(buf->vma)) {
> + printk(KERN_ERR "failed to get VMA\n");
> + ret = PTR_ERR(buf->vma);
> + goto fail_pages;
> + }
> +
> + /* extract page list from userspace mapping */
> + ret = vb2_dc_get_user_pages(start, pages, n_pages, buf->vma, write);
> if (ret) {
> - printk(KERN_ERR "Failed acquiring VMA for vaddr 0x%08lx\n",
> - vaddr);
> - kfree(buf);
> - return ERR_PTR(ret);
> + printk(KERN_ERR "failed to get user pages\n");
> + goto fail_vma;
> + }
> +
> + sgt = vb2_dc_pages_to_sgt(pages, n_pages, offset, offset2);
> + if (IS_ERR(sgt)) {
> + printk(KERN_ERR "failed to create scatterlist table\n");
> + ret = -ENOMEM;
> + goto fail_get_user_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_addr = dma_addr;
> - buf->vma = vma;
> + buf->dma_sgt = sgt;
> +
> + atomic_inc(&buf->refcount);
refcount is only used for MMAP buffers as far as I can tell, I don't think you
need to increment refcount here.
>
> return buf;
> -}
>
> -static void vb2_dc_put_userptr(void *mem_priv)
> -{
> - struct vb2_dc_buf *buf = mem_priv;
> +fail_map_sg:
> + dma_unmap_sg(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
>
> - if (!buf)
> - return;
> +fail_sgt:
> + if (!vma_is_io(buf->vma))
> + vb2_dc_sgt_foreach_page(sgt, put_page);
> + vb2_dc_release_sgtable(sgt);
> +
> +fail_get_user_pages:
> + if (pages && !vma_is_io(buf->vma))
> + while (n_pages)
> + put_page(pages[--n_pages]);
>
> +fail_vma:
> vb2_put_vma(buf->vma);
> +
> +fail_pages:
> + kfree(pages); /* kfree is NULL-proof */
> +
> +fail_buf:
> kfree(buf);
> +
> + return ERR_PTR(ret);
> }
>
> /*********************************************/
--
Regards,
Laurent Pinchart
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