1/*
2 * videobuf2-dma-sg.c - dma scatter/gather memory allocator for videobuf2
3 *
4 * Copyright (C) 2010 Samsung Electronics
5 *
6 * Author: Andrzej Pietrasiewicz <andrzejtp2010@gmail.com>
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation.
11 */
12
13#include <linux/module.h>
14#include <linux/mm.h>
15#include <linux/refcount.h>
16#include <linux/scatterlist.h>
17#include <linux/sched.h>
18#include <linux/slab.h>
19#include <linux/vmalloc.h>
20
21#include <media/videobuf2-v4l2.h>
22#include <media/videobuf2-memops.h>
23#include <media/videobuf2-dma-sg.h>
24
25static int debug;
26module_param(debug, int, 0644);
27
28#define dprintk(level, fmt, arg...) \
29 do { \
30 if (debug >= level) \
31 printk(KERN_DEBUG "vb2-dma-sg: " fmt, ## arg); \
32 } while (0)
33
34struct vb2_dma_sg_buf {
35 struct device *dev;
36 void *vaddr;
37 struct page **pages;
38 struct frame_vector *vec;
39 int offset;
40 enum dma_data_direction dma_dir;
41 struct sg_table sg_table;
42 /*
43 * This will point to sg_table when used with the MMAP or USERPTR
44 * memory model, and to the dma_buf sglist when used with the
45 * DMABUF memory model.
46 */
47 struct sg_table *dma_sgt;
48 size_t size;
49 unsigned int num_pages;
50 refcount_t refcount;
51 struct vb2_vmarea_handler handler;
52
53 struct dma_buf_attachment *db_attach;
54
55 struct vb2_buffer *vb;
56};
57
58static void vb2_dma_sg_put(void *buf_priv);
59
60static int vb2_dma_sg_alloc_compacted(struct vb2_dma_sg_buf *buf,
61 gfp_t gfp_flags)
62{
63 unsigned int last_page = 0;
64 unsigned long size = buf->size;
65
66 while (size > 0) {
67 struct page *pages;
68 int order;
69 int i;
70
71 order = get_order(size);
72 /* Don't over allocate*/
73 if ((PAGE_SIZE << order) > size)
74 order--;
75
76 pages = NULL;
77 while (!pages) {
78 pages = alloc_pages(GFP_KERNEL | __GFP_ZERO |
79 __GFP_NOWARN | gfp_flags, order);
80 if (pages)
81 break;
82
83 if (order == 0) {
84 while (last_page--)
85 __free_page(buf->pages[last_page]);
86 return -ENOMEM;
87 }
88 order--;
89 }
90
91 split_page(page: pages, order);
92 for (i = 0; i < (1 << order); i++)
93 buf->pages[last_page++] = &pages[i];
94
95 size -= PAGE_SIZE << order;
96 }
97
98 return 0;
99}
100
101static void *vb2_dma_sg_alloc(struct vb2_buffer *vb, struct device *dev,
102 unsigned long size)
103{
104 struct vb2_dma_sg_buf *buf;
105 struct sg_table *sgt;
106 int ret;
107 int num_pages;
108
109 if (WARN_ON(!dev) || WARN_ON(!size))
110 return ERR_PTR(error: -EINVAL);
111
112 buf = kzalloc(size: sizeof *buf, GFP_KERNEL);
113 if (!buf)
114 return ERR_PTR(error: -ENOMEM);
115
116 buf->vaddr = NULL;
117 buf->dma_dir = vb->vb2_queue->dma_dir;
118 buf->offset = 0;
119 buf->size = size;
120 /* size is already page aligned */
121 buf->num_pages = size >> PAGE_SHIFT;
122 buf->dma_sgt = &buf->sg_table;
123
124 /*
125 * NOTE: dma-sg allocates memory using the page allocator directly, so
126 * there is no memory consistency guarantee, hence dma-sg ignores DMA
127 * attributes passed from the upper layer.
128 */
129 buf->pages = kvcalloc(n: buf->num_pages, size: sizeof(struct page *), GFP_KERNEL);
130 if (!buf->pages)
131 goto fail_pages_array_alloc;
132
133 ret = vb2_dma_sg_alloc_compacted(buf, gfp_flags: vb->vb2_queue->gfp_flags);
134 if (ret)
135 goto fail_pages_alloc;
136
137 ret = sg_alloc_table_from_pages(sgt: buf->dma_sgt, pages: buf->pages,
138 n_pages: buf->num_pages, offset: 0, size, GFP_KERNEL);
139 if (ret)
140 goto fail_table_alloc;
141
142 /* Prevent the device from being released while the buffer is used */
143 buf->dev = get_device(dev);
144
145 sgt = &buf->sg_table;
146 /*
147 * No need to sync to the device, this will happen later when the
148 * prepare() memop is called.
149 */
150 if (dma_map_sgtable(dev: buf->dev, sgt, dir: buf->dma_dir,
151 DMA_ATTR_SKIP_CPU_SYNC))
152 goto fail_map;
153
154 buf->handler.refcount = &buf->refcount;
155 buf->handler.put = vb2_dma_sg_put;
156 buf->handler.arg = buf;
157 buf->vb = vb;
158
159 refcount_set(r: &buf->refcount, n: 1);
160
161 dprintk(1, "%s: Allocated buffer of %d pages\n",
162 __func__, buf->num_pages);
163 return buf;
164
165fail_map:
166 put_device(dev: buf->dev);
167 sg_free_table(buf->dma_sgt);
168fail_table_alloc:
169 num_pages = buf->num_pages;
170 while (num_pages--)
171 __free_page(buf->pages[num_pages]);
172fail_pages_alloc:
173 kvfree(addr: buf->pages);
174fail_pages_array_alloc:
175 kfree(objp: buf);
176 return ERR_PTR(error: -ENOMEM);
177}
178
179static void vb2_dma_sg_put(void *buf_priv)
180{
181 struct vb2_dma_sg_buf *buf = buf_priv;
182 struct sg_table *sgt = &buf->sg_table;
183 int i = buf->num_pages;
184
185 if (refcount_dec_and_test(r: &buf->refcount)) {
186 dprintk(1, "%s: Freeing buffer of %d pages\n", __func__,
187 buf->num_pages);
188 dma_unmap_sgtable(dev: buf->dev, sgt, dir: buf->dma_dir,
189 DMA_ATTR_SKIP_CPU_SYNC);
190 if (buf->vaddr)
191 vm_unmap_ram(mem: buf->vaddr, count: buf->num_pages);
192 sg_free_table(buf->dma_sgt);
193 while (--i >= 0)
194 __free_page(buf->pages[i]);
195 kvfree(addr: buf->pages);
196 put_device(dev: buf->dev);
197 kfree(objp: buf);
198 }
199}
200
201static void vb2_dma_sg_prepare(void *buf_priv)
202{
203 struct vb2_dma_sg_buf *buf = buf_priv;
204 struct sg_table *sgt = buf->dma_sgt;
205
206 if (buf->vb->skip_cache_sync_on_prepare)
207 return;
208
209 dma_sync_sgtable_for_device(dev: buf->dev, sgt, dir: buf->dma_dir);
210}
211
212static void vb2_dma_sg_finish(void *buf_priv)
213{
214 struct vb2_dma_sg_buf *buf = buf_priv;
215 struct sg_table *sgt = buf->dma_sgt;
216
217 if (buf->vb->skip_cache_sync_on_finish)
218 return;
219
220 dma_sync_sgtable_for_cpu(dev: buf->dev, sgt, dir: buf->dma_dir);
221}
222
223static void *vb2_dma_sg_get_userptr(struct vb2_buffer *vb, struct device *dev,
224 unsigned long vaddr, unsigned long size)
225{
226 struct vb2_dma_sg_buf *buf;
227 struct sg_table *sgt;
228 struct frame_vector *vec;
229
230 if (WARN_ON(!dev))
231 return ERR_PTR(error: -EINVAL);
232
233 buf = kzalloc(size: sizeof *buf, GFP_KERNEL);
234 if (!buf)
235 return ERR_PTR(error: -ENOMEM);
236
237 buf->vaddr = NULL;
238 buf->dev = dev;
239 buf->dma_dir = vb->vb2_queue->dma_dir;
240 buf->offset = vaddr & ~PAGE_MASK;
241 buf->size = size;
242 buf->dma_sgt = &buf->sg_table;
243 buf->vb = vb;
244 vec = vb2_create_framevec(start: vaddr, length: size,
245 write: buf->dma_dir == DMA_FROM_DEVICE ||
246 buf->dma_dir == DMA_BIDIRECTIONAL);
247 if (IS_ERR(ptr: vec))
248 goto userptr_fail_pfnvec;
249 buf->vec = vec;
250
251 buf->pages = frame_vector_pages(vec);
252 if (IS_ERR(ptr: buf->pages))
253 goto userptr_fail_sgtable;
254 buf->num_pages = frame_vector_count(vec);
255
256 if (sg_alloc_table_from_pages(sgt: buf->dma_sgt, pages: buf->pages,
257 n_pages: buf->num_pages, offset: buf->offset, size, gfp_mask: 0))
258 goto userptr_fail_sgtable;
259
260 sgt = &buf->sg_table;
261 /*
262 * No need to sync to the device, this will happen later when the
263 * prepare() memop is called.
264 */
265 if (dma_map_sgtable(dev: buf->dev, sgt, dir: buf->dma_dir,
266 DMA_ATTR_SKIP_CPU_SYNC))
267 goto userptr_fail_map;
268
269 return buf;
270
271userptr_fail_map:
272 sg_free_table(&buf->sg_table);
273userptr_fail_sgtable:
274 vb2_destroy_framevec(vec);
275userptr_fail_pfnvec:
276 kfree(objp: buf);
277 return ERR_PTR(error: -ENOMEM);
278}
279
280/*
281 * @put_userptr: inform the allocator that a USERPTR buffer will no longer
282 * be used
283 */
284static void vb2_dma_sg_put_userptr(void *buf_priv)
285{
286 struct vb2_dma_sg_buf *buf = buf_priv;
287 struct sg_table *sgt = &buf->sg_table;
288 int i = buf->num_pages;
289
290 dprintk(1, "%s: Releasing userspace buffer of %d pages\n",
291 __func__, buf->num_pages);
292 dma_unmap_sgtable(dev: buf->dev, sgt, dir: buf->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
293 if (buf->vaddr)
294 vm_unmap_ram(mem: buf->vaddr, count: buf->num_pages);
295 sg_free_table(buf->dma_sgt);
296 if (buf->dma_dir == DMA_FROM_DEVICE ||
297 buf->dma_dir == DMA_BIDIRECTIONAL)
298 while (--i >= 0)
299 set_page_dirty_lock(buf->pages[i]);
300 vb2_destroy_framevec(vec: buf->vec);
301 kfree(objp: buf);
302}
303
304static void *vb2_dma_sg_vaddr(struct vb2_buffer *vb, void *buf_priv)
305{
306 struct vb2_dma_sg_buf *buf = buf_priv;
307 struct iosys_map map;
308 int ret;
309
310 BUG_ON(!buf);
311
312 if (!buf->vaddr) {
313 if (buf->db_attach) {
314 ret = dma_buf_vmap_unlocked(dmabuf: buf->db_attach->dmabuf, map: &map);
315 buf->vaddr = ret ? NULL : map.vaddr;
316 } else {
317 buf->vaddr = vm_map_ram(pages: buf->pages, count: buf->num_pages, node: -1);
318 }
319 }
320
321 /* add offset in case userptr is not page-aligned */
322 return buf->vaddr ? buf->vaddr + buf->offset : NULL;
323}
324
325static unsigned int vb2_dma_sg_num_users(void *buf_priv)
326{
327 struct vb2_dma_sg_buf *buf = buf_priv;
328
329 return refcount_read(r: &buf->refcount);
330}
331
332static int vb2_dma_sg_mmap(void *buf_priv, struct vm_area_struct *vma)
333{
334 struct vb2_dma_sg_buf *buf = buf_priv;
335 int err;
336
337 if (!buf) {
338 printk(KERN_ERR "No memory to map\n");
339 return -EINVAL;
340 }
341
342 err = vm_map_pages(vma, pages: buf->pages, num: buf->num_pages);
343 if (err) {
344 printk(KERN_ERR "Remapping memory, error: %d\n", err);
345 return err;
346 }
347
348 /*
349 * Use common vm_area operations to track buffer refcount.
350 */
351 vma->vm_private_data = &buf->handler;
352 vma->vm_ops = &vb2_common_vm_ops;
353
354 vma->vm_ops->open(vma);
355
356 return 0;
357}
358
359/*********************************************/
360/* DMABUF ops for exporters */
361/*********************************************/
362
363struct vb2_dma_sg_attachment {
364 struct sg_table sgt;
365 enum dma_data_direction dma_dir;
366};
367
368static int vb2_dma_sg_dmabuf_ops_attach(struct dma_buf *dbuf,
369 struct dma_buf_attachment *dbuf_attach)
370{
371 struct vb2_dma_sg_attachment *attach;
372 unsigned int i;
373 struct scatterlist *rd, *wr;
374 struct sg_table *sgt;
375 struct vb2_dma_sg_buf *buf = dbuf->priv;
376 int ret;
377
378 attach = kzalloc(size: sizeof(*attach), GFP_KERNEL);
379 if (!attach)
380 return -ENOMEM;
381
382 sgt = &attach->sgt;
383 /* Copy the buf->base_sgt scatter list to the attachment, as we can't
384 * map the same scatter list to multiple attachments at the same time.
385 */
386 ret = sg_alloc_table(sgt, buf->dma_sgt->orig_nents, GFP_KERNEL);
387 if (ret) {
388 kfree(objp: attach);
389 return -ENOMEM;
390 }
391
392 rd = buf->dma_sgt->sgl;
393 wr = sgt->sgl;
394 for (i = 0; i < sgt->orig_nents; ++i) {
395 sg_set_page(sg: wr, page: sg_page(sg: rd), len: rd->length, offset: rd->offset);
396 rd = sg_next(rd);
397 wr = sg_next(wr);
398 }
399
400 attach->dma_dir = DMA_NONE;
401 dbuf_attach->priv = attach;
402
403 return 0;
404}
405
406static void vb2_dma_sg_dmabuf_ops_detach(struct dma_buf *dbuf,
407 struct dma_buf_attachment *db_attach)
408{
409 struct vb2_dma_sg_attachment *attach = db_attach->priv;
410 struct sg_table *sgt;
411
412 if (!attach)
413 return;
414
415 sgt = &attach->sgt;
416
417 /* release the scatterlist cache */
418 if (attach->dma_dir != DMA_NONE)
419 dma_unmap_sgtable(dev: db_attach->dev, sgt, dir: attach->dma_dir, attrs: 0);
420 sg_free_table(sgt);
421 kfree(objp: attach);
422 db_attach->priv = NULL;
423}
424
425static struct sg_table *vb2_dma_sg_dmabuf_ops_map(
426 struct dma_buf_attachment *db_attach, enum dma_data_direction dma_dir)
427{
428 struct vb2_dma_sg_attachment *attach = db_attach->priv;
429 struct sg_table *sgt;
430
431 sgt = &attach->sgt;
432 /* return previously mapped sg table */
433 if (attach->dma_dir == dma_dir)
434 return sgt;
435
436 /* release any previous cache */
437 if (attach->dma_dir != DMA_NONE) {
438 dma_unmap_sgtable(dev: db_attach->dev, sgt, dir: attach->dma_dir, attrs: 0);
439 attach->dma_dir = DMA_NONE;
440 }
441
442 /* mapping to the client with new direction */
443 if (dma_map_sgtable(dev: db_attach->dev, sgt, dir: dma_dir, attrs: 0)) {
444 pr_err("failed to map scatterlist\n");
445 return ERR_PTR(error: -EIO);
446 }
447
448 attach->dma_dir = dma_dir;
449
450 return sgt;
451}
452
453static void vb2_dma_sg_dmabuf_ops_unmap(struct dma_buf_attachment *db_attach,
454 struct sg_table *sgt, enum dma_data_direction dma_dir)
455{
456 /* nothing to be done here */
457}
458
459static void vb2_dma_sg_dmabuf_ops_release(struct dma_buf *dbuf)
460{
461 /* drop reference obtained in vb2_dma_sg_get_dmabuf */
462 vb2_dma_sg_put(buf_priv: dbuf->priv);
463}
464
465static int
466vb2_dma_sg_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
467 enum dma_data_direction direction)
468{
469 struct vb2_dma_sg_buf *buf = dbuf->priv;
470 struct sg_table *sgt = buf->dma_sgt;
471
472 dma_sync_sg_for_cpu(dev: buf->dev, sg: sgt->sgl, nelems: sgt->nents, dir: buf->dma_dir);
473 return 0;
474}
475
476static int
477vb2_dma_sg_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf,
478 enum dma_data_direction direction)
479{
480 struct vb2_dma_sg_buf *buf = dbuf->priv;
481 struct sg_table *sgt = buf->dma_sgt;
482
483 dma_sync_sg_for_device(dev: buf->dev, sg: sgt->sgl, nelems: sgt->nents, dir: buf->dma_dir);
484 return 0;
485}
486
487static int vb2_dma_sg_dmabuf_ops_vmap(struct dma_buf *dbuf,
488 struct iosys_map *map)
489{
490 struct vb2_dma_sg_buf *buf;
491 void *vaddr;
492
493 buf = dbuf->priv;
494 vaddr = vb2_dma_sg_vaddr(vb: buf->vb, buf_priv: buf);
495 if (!vaddr)
496 return -EINVAL;
497
498 iosys_map_set_vaddr(map, vaddr);
499
500 return 0;
501}
502
503static int vb2_dma_sg_dmabuf_ops_mmap(struct dma_buf *dbuf,
504 struct vm_area_struct *vma)
505{
506 return vb2_dma_sg_mmap(buf_priv: dbuf->priv, vma);
507}
508
509static const struct dma_buf_ops vb2_dma_sg_dmabuf_ops = {
510 .attach = vb2_dma_sg_dmabuf_ops_attach,
511 .detach = vb2_dma_sg_dmabuf_ops_detach,
512 .map_dma_buf = vb2_dma_sg_dmabuf_ops_map,
513 .unmap_dma_buf = vb2_dma_sg_dmabuf_ops_unmap,
514 .begin_cpu_access = vb2_dma_sg_dmabuf_ops_begin_cpu_access,
515 .end_cpu_access = vb2_dma_sg_dmabuf_ops_end_cpu_access,
516 .vmap = vb2_dma_sg_dmabuf_ops_vmap,
517 .mmap = vb2_dma_sg_dmabuf_ops_mmap,
518 .release = vb2_dma_sg_dmabuf_ops_release,
519};
520
521static struct dma_buf *vb2_dma_sg_get_dmabuf(struct vb2_buffer *vb,
522 void *buf_priv,
523 unsigned long flags)
524{
525 struct vb2_dma_sg_buf *buf = buf_priv;
526 struct dma_buf *dbuf;
527 DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
528
529 exp_info.ops = &vb2_dma_sg_dmabuf_ops;
530 exp_info.size = buf->size;
531 exp_info.flags = flags;
532 exp_info.priv = buf;
533
534 if (WARN_ON(!buf->dma_sgt))
535 return NULL;
536
537 dbuf = dma_buf_export(exp_info: &exp_info);
538 if (IS_ERR(ptr: dbuf))
539 return NULL;
540
541 /* dmabuf keeps reference to vb2 buffer */
542 refcount_inc(r: &buf->refcount);
543
544 return dbuf;
545}
546
547/*********************************************/
548/* callbacks for DMABUF buffers */
549/*********************************************/
550
551static int vb2_dma_sg_map_dmabuf(void *mem_priv)
552{
553 struct vb2_dma_sg_buf *buf = mem_priv;
554 struct sg_table *sgt;
555
556 if (WARN_ON(!buf->db_attach)) {
557 pr_err("trying to pin a non attached buffer\n");
558 return -EINVAL;
559 }
560
561 if (WARN_ON(buf->dma_sgt)) {
562 pr_err("dmabuf buffer is already pinned\n");
563 return 0;
564 }
565
566 /* get the associated scatterlist for this buffer */
567 sgt = dma_buf_map_attachment_unlocked(attach: buf->db_attach, direction: buf->dma_dir);
568 if (IS_ERR(ptr: sgt)) {
569 pr_err("Error getting dmabuf scatterlist\n");
570 return -EINVAL;
571 }
572
573 buf->dma_sgt = sgt;
574 buf->vaddr = NULL;
575
576 return 0;
577}
578
579static void vb2_dma_sg_unmap_dmabuf(void *mem_priv)
580{
581 struct vb2_dma_sg_buf *buf = mem_priv;
582 struct sg_table *sgt = buf->dma_sgt;
583 struct iosys_map map = IOSYS_MAP_INIT_VADDR(buf->vaddr);
584
585 if (WARN_ON(!buf->db_attach)) {
586 pr_err("trying to unpin a not attached buffer\n");
587 return;
588 }
589
590 if (WARN_ON(!sgt)) {
591 pr_err("dmabuf buffer is already unpinned\n");
592 return;
593 }
594
595 if (buf->vaddr) {
596 dma_buf_vunmap_unlocked(dmabuf: buf->db_attach->dmabuf, map: &map);
597 buf->vaddr = NULL;
598 }
599 dma_buf_unmap_attachment_unlocked(attach: buf->db_attach, sg_table: sgt, direction: buf->dma_dir);
600
601 buf->dma_sgt = NULL;
602}
603
604static void vb2_dma_sg_detach_dmabuf(void *mem_priv)
605{
606 struct vb2_dma_sg_buf *buf = mem_priv;
607
608 /* if vb2 works correctly you should never detach mapped buffer */
609 if (WARN_ON(buf->dma_sgt))
610 vb2_dma_sg_unmap_dmabuf(mem_priv: buf);
611
612 /* detach this attachment */
613 dma_buf_detach(dmabuf: buf->db_attach->dmabuf, attach: buf->db_attach);
614 kfree(objp: buf);
615}
616
617static void *vb2_dma_sg_attach_dmabuf(struct vb2_buffer *vb, struct device *dev,
618 struct dma_buf *dbuf, unsigned long size)
619{
620 struct vb2_dma_sg_buf *buf;
621 struct dma_buf_attachment *dba;
622
623 if (WARN_ON(!dev))
624 return ERR_PTR(error: -EINVAL);
625
626 if (dbuf->size < size)
627 return ERR_PTR(error: -EFAULT);
628
629 buf = kzalloc(size: sizeof(*buf), GFP_KERNEL);
630 if (!buf)
631 return ERR_PTR(error: -ENOMEM);
632
633 buf->dev = dev;
634 /* create attachment for the dmabuf with the user device */
635 dba = dma_buf_attach(dmabuf: dbuf, dev: buf->dev);
636 if (IS_ERR(ptr: dba)) {
637 pr_err("failed to attach dmabuf\n");
638 kfree(objp: buf);
639 return dba;
640 }
641
642 buf->dma_dir = vb->vb2_queue->dma_dir;
643 buf->size = size;
644 buf->db_attach = dba;
645 buf->vb = vb;
646
647 return buf;
648}
649
650static void *vb2_dma_sg_cookie(struct vb2_buffer *vb, void *buf_priv)
651{
652 struct vb2_dma_sg_buf *buf = buf_priv;
653
654 return buf->dma_sgt;
655}
656
657const struct vb2_mem_ops vb2_dma_sg_memops = {
658 .alloc = vb2_dma_sg_alloc,
659 .put = vb2_dma_sg_put,
660 .get_userptr = vb2_dma_sg_get_userptr,
661 .put_userptr = vb2_dma_sg_put_userptr,
662 .prepare = vb2_dma_sg_prepare,
663 .finish = vb2_dma_sg_finish,
664 .vaddr = vb2_dma_sg_vaddr,
665 .mmap = vb2_dma_sg_mmap,
666 .num_users = vb2_dma_sg_num_users,
667 .get_dmabuf = vb2_dma_sg_get_dmabuf,
668 .map_dmabuf = vb2_dma_sg_map_dmabuf,
669 .unmap_dmabuf = vb2_dma_sg_unmap_dmabuf,
670 .attach_dmabuf = vb2_dma_sg_attach_dmabuf,
671 .detach_dmabuf = vb2_dma_sg_detach_dmabuf,
672 .cookie = vb2_dma_sg_cookie,
673};
674EXPORT_SYMBOL_GPL(vb2_dma_sg_memops);
675
676MODULE_DESCRIPTION("dma scatter/gather memory handling routines for videobuf2");
677MODULE_AUTHOR("Andrzej Pietrasiewicz");
678MODULE_LICENSE("GPL");
679MODULE_IMPORT_NS(DMA_BUF);
680

source code of linux/drivers/media/common/videobuf2/videobuf2-dma-sg.c