Hi Tomasz,
On Thursday 05 April 2012 16:00:05 Tomasz Stanislawski wrote:
From: Andrzej Pietrasiewicz andrzej.p@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@samsung.com Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com [bugfixing] Signed-off-by: Kamil Debski k.debski@samsung.com [bugfixing] Signed-off-by: Tomasz Stanislawski t.stanislaws@samsung.com [add sglist subroutines/code refactoring] Signed-off-by: Kyungmin Park kyungmin.park@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);
}
/*********************************************/