1 /*
2  * videobuf2-dma-contig.c - DMA contig memory allocator for videobuf2
3  *
4  * Copyright (C) 2010 Samsung Electronics
5  *
6  * Author: Pawel Osciak <pawel@osciak.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/dma-buf.h>
14 #include <linux/module.h>
15 #include <linux/refcount.h>
16 #include <linux/scatterlist.h>
17 #include <linux/sched.h>
18 #include <linux/slab.h>
19 #include <linux/dma-mapping.h>
20 
21 #include <media/videobuf2-v4l2.h>
22 #include <media/videobuf2-dma-contig.h>
23 #include <media/videobuf2-memops.h>
24 
25 struct vb2_dc_buf {
26 	struct device			*dev;
27 	void				*vaddr;
28 	unsigned long			size;
29 	void				*cookie;
30 	dma_addr_t			dma_addr;
31 	unsigned long			attrs;
32 	enum dma_data_direction		dma_dir;
33 	struct sg_table			*dma_sgt;
34 	struct frame_vector		*vec;
35 
36 	/* MMAP related */
37 	struct vb2_vmarea_handler	handler;
38 	refcount_t			refcount;
39 	struct sg_table			*sgt_base;
40 
41 	/* DMABUF related */
42 	struct dma_buf_attachment	*db_attach;
43 };
44 
45 /*********************************************/
46 /*        scatterlist table functions        */
47 /*********************************************/
48 
49 static unsigned long vb2_dc_get_contiguous_size(struct sg_table *sgt)
50 {
51 	struct scatterlist *s;
52 	dma_addr_t expected = sg_dma_address(sgt->sgl);
53 	unsigned int i;
54 	unsigned long size = 0;
55 
56 	for_each_sg(sgt->sgl, s, sgt->nents, i) {
57 		if (sg_dma_address(s) != expected)
58 			break;
59 		expected = sg_dma_address(s) + sg_dma_len(s);
60 		size += sg_dma_len(s);
61 	}
62 	return size;
63 }
64 
65 /*********************************************/
66 /*         callbacks for all buffers         */
67 /*********************************************/
68 
69 static void *vb2_dc_cookie(void *buf_priv)
70 {
71 	struct vb2_dc_buf *buf = buf_priv;
72 
73 	return &buf->dma_addr;
74 }
75 
76 static void *vb2_dc_vaddr(void *buf_priv)
77 {
78 	struct vb2_dc_buf *buf = buf_priv;
79 
80 	if (!buf->vaddr && buf->db_attach)
81 		buf->vaddr = dma_buf_vmap(buf->db_attach->dmabuf);
82 
83 	return buf->vaddr;
84 }
85 
86 static unsigned int vb2_dc_num_users(void *buf_priv)
87 {
88 	struct vb2_dc_buf *buf = buf_priv;
89 
90 	return refcount_read(&buf->refcount);
91 }
92 
93 static void vb2_dc_prepare(void *buf_priv)
94 {
95 	struct vb2_dc_buf *buf = buf_priv;
96 	struct sg_table *sgt = buf->dma_sgt;
97 
98 	/* DMABUF exporter will flush the cache for us */
99 	if (!sgt || buf->db_attach)
100 		return;
101 
102 	dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->orig_nents,
103 			       buf->dma_dir);
104 }
105 
106 static void vb2_dc_finish(void *buf_priv)
107 {
108 	struct vb2_dc_buf *buf = buf_priv;
109 	struct sg_table *sgt = buf->dma_sgt;
110 
111 	/* DMABUF exporter will flush the cache for us */
112 	if (!sgt || buf->db_attach)
113 		return;
114 
115 	dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->orig_nents, buf->dma_dir);
116 }
117 
118 /*********************************************/
119 /*        callbacks for MMAP buffers         */
120 /*********************************************/
121 
122 static void vb2_dc_put(void *buf_priv)
123 {
124 	struct vb2_dc_buf *buf = buf_priv;
125 
126 	if (!refcount_dec_and_test(&buf->refcount))
127 		return;
128 
129 	if (buf->sgt_base) {
130 		sg_free_table(buf->sgt_base);
131 		kfree(buf->sgt_base);
132 	}
133 	dma_free_attrs(buf->dev, buf->size, buf->cookie, buf->dma_addr,
134 		       buf->attrs);
135 	put_device(buf->dev);
136 	kfree(buf);
137 }
138 
139 static void *vb2_dc_alloc(struct device *dev, unsigned long attrs,
140 			  unsigned long size, enum dma_data_direction dma_dir,
141 			  gfp_t gfp_flags)
142 {
143 	struct vb2_dc_buf *buf;
144 
145 	if (WARN_ON(!dev))
146 		return ERR_PTR(-EINVAL);
147 
148 	buf = kzalloc(sizeof *buf, GFP_KERNEL);
149 	if (!buf)
150 		return ERR_PTR(-ENOMEM);
151 
152 	if (attrs)
153 		buf->attrs = attrs;
154 	buf->cookie = dma_alloc_attrs(dev, size, &buf->dma_addr,
155 					GFP_KERNEL | gfp_flags, buf->attrs);
156 	if (!buf->cookie) {
157 		dev_err(dev, "dma_alloc_coherent of size %ld failed\n", size);
158 		kfree(buf);
159 		return ERR_PTR(-ENOMEM);
160 	}
161 
162 	if ((buf->attrs & DMA_ATTR_NO_KERNEL_MAPPING) == 0)
163 		buf->vaddr = buf->cookie;
164 
165 	/* Prevent the device from being released while the buffer is used */
166 	buf->dev = get_device(dev);
167 	buf->size = size;
168 	buf->dma_dir = dma_dir;
169 
170 	buf->handler.refcount = &buf->refcount;
171 	buf->handler.put = vb2_dc_put;
172 	buf->handler.arg = buf;
173 
174 	refcount_set(&buf->refcount, 1);
175 
176 	return buf;
177 }
178 
179 static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma)
180 {
181 	struct vb2_dc_buf *buf = buf_priv;
182 	int ret;
183 
184 	if (!buf) {
185 		printk(KERN_ERR "No buffer to map\n");
186 		return -EINVAL;
187 	}
188 
189 	ret = dma_mmap_attrs(buf->dev, vma, buf->cookie,
190 		buf->dma_addr, buf->size, buf->attrs);
191 
192 	if (ret) {
193 		pr_err("Remapping memory failed, error: %d\n", ret);
194 		return ret;
195 	}
196 
197 	vma->vm_flags		|= VM_DONTEXPAND | VM_DONTDUMP;
198 	vma->vm_private_data	= &buf->handler;
199 	vma->vm_ops		= &vb2_common_vm_ops;
200 
201 	vma->vm_ops->open(vma);
202 
203 	pr_debug("%s: mapped dma addr 0x%08lx at 0x%08lx, size %ld\n",
204 		__func__, (unsigned long)buf->dma_addr, vma->vm_start,
205 		buf->size);
206 
207 	return 0;
208 }
209 
210 /*********************************************/
211 /*         DMABUF ops for exporters          */
212 /*********************************************/
213 
214 struct vb2_dc_attachment {
215 	struct sg_table sgt;
216 	enum dma_data_direction dma_dir;
217 };
218 
219 static int vb2_dc_dmabuf_ops_attach(struct dma_buf *dbuf,
220 	struct dma_buf_attachment *dbuf_attach)
221 {
222 	struct vb2_dc_attachment *attach;
223 	unsigned int i;
224 	struct scatterlist *rd, *wr;
225 	struct sg_table *sgt;
226 	struct vb2_dc_buf *buf = dbuf->priv;
227 	int ret;
228 
229 	attach = kzalloc(sizeof(*attach), GFP_KERNEL);
230 	if (!attach)
231 		return -ENOMEM;
232 
233 	sgt = &attach->sgt;
234 	/* Copy the buf->base_sgt scatter list to the attachment, as we can't
235 	 * map the same scatter list to multiple attachments at the same time.
236 	 */
237 	ret = sg_alloc_table(sgt, buf->sgt_base->orig_nents, GFP_KERNEL);
238 	if (ret) {
239 		kfree(attach);
240 		return -ENOMEM;
241 	}
242 
243 	rd = buf->sgt_base->sgl;
244 	wr = sgt->sgl;
245 	for (i = 0; i < sgt->orig_nents; ++i) {
246 		sg_set_page(wr, sg_page(rd), rd->length, rd->offset);
247 		rd = sg_next(rd);
248 		wr = sg_next(wr);
249 	}
250 
251 	attach->dma_dir = DMA_NONE;
252 	dbuf_attach->priv = attach;
253 
254 	return 0;
255 }
256 
257 static void vb2_dc_dmabuf_ops_detach(struct dma_buf *dbuf,
258 	struct dma_buf_attachment *db_attach)
259 {
260 	struct vb2_dc_attachment *attach = db_attach->priv;
261 	struct sg_table *sgt;
262 
263 	if (!attach)
264 		return;
265 
266 	sgt = &attach->sgt;
267 
268 	/* release the scatterlist cache */
269 	if (attach->dma_dir != DMA_NONE)
270 		/*
271 		 * Cache sync can be skipped here, as the vb2_dc memory is
272 		 * allocated from device coherent memory, which means the
273 		 * memory locations do not require any explicit cache
274 		 * maintenance prior or after being used by the device.
275 		 */
276 		dma_unmap_sg_attrs(db_attach->dev, sgt->sgl, sgt->orig_nents,
277 				   attach->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
278 	sg_free_table(sgt);
279 	kfree(attach);
280 	db_attach->priv = NULL;
281 }
282 
283 static struct sg_table *vb2_dc_dmabuf_ops_map(
284 	struct dma_buf_attachment *db_attach, enum dma_data_direction dma_dir)
285 {
286 	struct vb2_dc_attachment *attach = db_attach->priv;
287 	/* stealing dmabuf mutex to serialize map/unmap operations */
288 	struct mutex *lock = &db_attach->dmabuf->lock;
289 	struct sg_table *sgt;
290 
291 	mutex_lock(lock);
292 
293 	sgt = &attach->sgt;
294 	/* return previously mapped sg table */
295 	if (attach->dma_dir == dma_dir) {
296 		mutex_unlock(lock);
297 		return sgt;
298 	}
299 
300 	/* release any previous cache */
301 	if (attach->dma_dir != DMA_NONE) {
302 		dma_unmap_sg_attrs(db_attach->dev, sgt->sgl, sgt->orig_nents,
303 				   attach->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
304 		attach->dma_dir = DMA_NONE;
305 	}
306 
307 	/*
308 	 * mapping to the client with new direction, no cache sync
309 	 * required see comment in vb2_dc_dmabuf_ops_detach()
310 	 */
311 	sgt->nents = dma_map_sg_attrs(db_attach->dev, sgt->sgl, sgt->orig_nents,
312 				      dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
313 	if (!sgt->nents) {
314 		pr_err("failed to map scatterlist\n");
315 		mutex_unlock(lock);
316 		return ERR_PTR(-EIO);
317 	}
318 
319 	attach->dma_dir = dma_dir;
320 
321 	mutex_unlock(lock);
322 
323 	return sgt;
324 }
325 
326 static void vb2_dc_dmabuf_ops_unmap(struct dma_buf_attachment *db_attach,
327 	struct sg_table *sgt, enum dma_data_direction dma_dir)
328 {
329 	/* nothing to be done here */
330 }
331 
332 static void vb2_dc_dmabuf_ops_release(struct dma_buf *dbuf)
333 {
334 	/* drop reference obtained in vb2_dc_get_dmabuf */
335 	vb2_dc_put(dbuf->priv);
336 }
337 
338 static void *vb2_dc_dmabuf_ops_vmap(struct dma_buf *dbuf)
339 {
340 	struct vb2_dc_buf *buf = dbuf->priv;
341 
342 	return buf->vaddr;
343 }
344 
345 static int vb2_dc_dmabuf_ops_mmap(struct dma_buf *dbuf,
346 	struct vm_area_struct *vma)
347 {
348 	return vb2_dc_mmap(dbuf->priv, vma);
349 }
350 
351 static const struct dma_buf_ops vb2_dc_dmabuf_ops = {
352 	.attach = vb2_dc_dmabuf_ops_attach,
353 	.detach = vb2_dc_dmabuf_ops_detach,
354 	.map_dma_buf = vb2_dc_dmabuf_ops_map,
355 	.unmap_dma_buf = vb2_dc_dmabuf_ops_unmap,
356 	.vmap = vb2_dc_dmabuf_ops_vmap,
357 	.mmap = vb2_dc_dmabuf_ops_mmap,
358 	.release = vb2_dc_dmabuf_ops_release,
359 };
360 
361 static struct sg_table *vb2_dc_get_base_sgt(struct vb2_dc_buf *buf)
362 {
363 	int ret;
364 	struct sg_table *sgt;
365 
366 	sgt = kmalloc(sizeof(*sgt), GFP_KERNEL);
367 	if (!sgt) {
368 		dev_err(buf->dev, "failed to alloc sg table\n");
369 		return NULL;
370 	}
371 
372 	ret = dma_get_sgtable_attrs(buf->dev, sgt, buf->cookie, buf->dma_addr,
373 		buf->size, buf->attrs);
374 	if (ret < 0) {
375 		dev_err(buf->dev, "failed to get scatterlist from DMA API\n");
376 		kfree(sgt);
377 		return NULL;
378 	}
379 
380 	return sgt;
381 }
382 
383 static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv, unsigned long flags)
384 {
385 	struct vb2_dc_buf *buf = buf_priv;
386 	struct dma_buf *dbuf;
387 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
388 
389 	exp_info.ops = &vb2_dc_dmabuf_ops;
390 	exp_info.size = buf->size;
391 	exp_info.flags = flags;
392 	exp_info.priv = buf;
393 
394 	if (!buf->sgt_base)
395 		buf->sgt_base = vb2_dc_get_base_sgt(buf);
396 
397 	if (WARN_ON(!buf->sgt_base))
398 		return NULL;
399 
400 	dbuf = dma_buf_export(&exp_info);
401 	if (IS_ERR(dbuf))
402 		return NULL;
403 
404 	/* dmabuf keeps reference to vb2 buffer */
405 	refcount_inc(&buf->refcount);
406 
407 	return dbuf;
408 }
409 
410 /*********************************************/
411 /*       callbacks for USERPTR buffers       */
412 /*********************************************/
413 
414 static void vb2_dc_put_userptr(void *buf_priv)
415 {
416 	struct vb2_dc_buf *buf = buf_priv;
417 	struct sg_table *sgt = buf->dma_sgt;
418 	int i;
419 	struct page **pages;
420 
421 	if (sgt) {
422 		/*
423 		 * No need to sync to CPU, it's already synced to the CPU
424 		 * since the finish() memop will have been called before this.
425 		 */
426 		dma_unmap_sg_attrs(buf->dev, sgt->sgl, sgt->orig_nents,
427 				   buf->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
428 		pages = frame_vector_pages(buf->vec);
429 		/* sgt should exist only if vector contains pages... */
430 		BUG_ON(IS_ERR(pages));
431 		if (buf->dma_dir == DMA_FROM_DEVICE ||
432 		    buf->dma_dir == DMA_BIDIRECTIONAL)
433 			for (i = 0; i < frame_vector_count(buf->vec); i++)
434 				set_page_dirty_lock(pages[i]);
435 		sg_free_table(sgt);
436 		kfree(sgt);
437 	} else {
438 		dma_unmap_resource(buf->dev, buf->dma_addr, buf->size,
439 				   buf->dma_dir, 0);
440 	}
441 	vb2_destroy_framevec(buf->vec);
442 	kfree(buf);
443 }
444 
445 static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr,
446 	unsigned long size, enum dma_data_direction dma_dir)
447 {
448 	struct vb2_dc_buf *buf;
449 	struct frame_vector *vec;
450 	unsigned int offset;
451 	int n_pages, i;
452 	int ret = 0;
453 	struct sg_table *sgt;
454 	unsigned long contig_size;
455 	unsigned long dma_align = dma_get_cache_alignment();
456 
457 	/* Only cache aligned DMA transfers are reliable */
458 	if (!IS_ALIGNED(vaddr | size, dma_align)) {
459 		pr_debug("user data must be aligned to %lu bytes\n", dma_align);
460 		return ERR_PTR(-EINVAL);
461 	}
462 
463 	if (!size) {
464 		pr_debug("size is zero\n");
465 		return ERR_PTR(-EINVAL);
466 	}
467 
468 	if (WARN_ON(!dev))
469 		return ERR_PTR(-EINVAL);
470 
471 	buf = kzalloc(sizeof *buf, GFP_KERNEL);
472 	if (!buf)
473 		return ERR_PTR(-ENOMEM);
474 
475 	buf->dev = dev;
476 	buf->dma_dir = dma_dir;
477 
478 	offset = lower_32_bits(offset_in_page(vaddr));
479 	vec = vb2_create_framevec(vaddr, size);
480 	if (IS_ERR(vec)) {
481 		ret = PTR_ERR(vec);
482 		goto fail_buf;
483 	}
484 	buf->vec = vec;
485 	n_pages = frame_vector_count(vec);
486 	ret = frame_vector_to_pages(vec);
487 	if (ret < 0) {
488 		unsigned long *nums = frame_vector_pfns(vec);
489 
490 		/*
491 		 * Failed to convert to pages... Check the memory is physically
492 		 * contiguous and use direct mapping
493 		 */
494 		for (i = 1; i < n_pages; i++)
495 			if (nums[i-1] + 1 != nums[i])
496 				goto fail_pfnvec;
497 		buf->dma_addr = dma_map_resource(buf->dev,
498 				__pfn_to_phys(nums[0]), size, buf->dma_dir, 0);
499 		if (dma_mapping_error(buf->dev, buf->dma_addr)) {
500 			ret = -ENOMEM;
501 			goto fail_pfnvec;
502 		}
503 		goto out;
504 	}
505 
506 	sgt = kzalloc(sizeof(*sgt), GFP_KERNEL);
507 	if (!sgt) {
508 		pr_err("failed to allocate sg table\n");
509 		ret = -ENOMEM;
510 		goto fail_pfnvec;
511 	}
512 
513 	ret = sg_alloc_table_from_pages(sgt, frame_vector_pages(vec), n_pages,
514 		offset, size, GFP_KERNEL);
515 	if (ret) {
516 		pr_err("failed to initialize sg table\n");
517 		goto fail_sgt;
518 	}
519 
520 	/*
521 	 * No need to sync to the device, this will happen later when the
522 	 * prepare() memop is called.
523 	 */
524 	sgt->nents = dma_map_sg_attrs(buf->dev, sgt->sgl, sgt->orig_nents,
525 				      buf->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
526 	if (sgt->nents <= 0) {
527 		pr_err("failed to map scatterlist\n");
528 		ret = -EIO;
529 		goto fail_sgt_init;
530 	}
531 
532 	contig_size = vb2_dc_get_contiguous_size(sgt);
533 	if (contig_size < size) {
534 		pr_err("contiguous mapping is too small %lu/%lu\n",
535 			contig_size, size);
536 		ret = -EFAULT;
537 		goto fail_map_sg;
538 	}
539 
540 	buf->dma_addr = sg_dma_address(sgt->sgl);
541 	buf->dma_sgt = sgt;
542 out:
543 	buf->size = size;
544 
545 	return buf;
546 
547 fail_map_sg:
548 	dma_unmap_sg_attrs(buf->dev, sgt->sgl, sgt->orig_nents,
549 			   buf->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
550 
551 fail_sgt_init:
552 	sg_free_table(sgt);
553 
554 fail_sgt:
555 	kfree(sgt);
556 
557 fail_pfnvec:
558 	vb2_destroy_framevec(vec);
559 
560 fail_buf:
561 	kfree(buf);
562 
563 	return ERR_PTR(ret);
564 }
565 
566 /*********************************************/
567 /*       callbacks for DMABUF buffers        */
568 /*********************************************/
569 
570 static int vb2_dc_map_dmabuf(void *mem_priv)
571 {
572 	struct vb2_dc_buf *buf = mem_priv;
573 	struct sg_table *sgt;
574 	unsigned long contig_size;
575 
576 	if (WARN_ON(!buf->db_attach)) {
577 		pr_err("trying to pin a non attached buffer\n");
578 		return -EINVAL;
579 	}
580 
581 	if (WARN_ON(buf->dma_sgt)) {
582 		pr_err("dmabuf buffer is already pinned\n");
583 		return 0;
584 	}
585 
586 	/* get the associated scatterlist for this buffer */
587 	sgt = dma_buf_map_attachment(buf->db_attach, buf->dma_dir);
588 	if (IS_ERR(sgt)) {
589 		pr_err("Error getting dmabuf scatterlist\n");
590 		return -EINVAL;
591 	}
592 
593 	/* checking if dmabuf is big enough to store contiguous chunk */
594 	contig_size = vb2_dc_get_contiguous_size(sgt);
595 	if (contig_size < buf->size) {
596 		pr_err("contiguous chunk is too small %lu/%lu\n",
597 		       contig_size, buf->size);
598 		dma_buf_unmap_attachment(buf->db_attach, sgt, buf->dma_dir);
599 		return -EFAULT;
600 	}
601 
602 	buf->dma_addr = sg_dma_address(sgt->sgl);
603 	buf->dma_sgt = sgt;
604 	buf->vaddr = NULL;
605 
606 	return 0;
607 }
608 
609 static void vb2_dc_unmap_dmabuf(void *mem_priv)
610 {
611 	struct vb2_dc_buf *buf = mem_priv;
612 	struct sg_table *sgt = buf->dma_sgt;
613 
614 	if (WARN_ON(!buf->db_attach)) {
615 		pr_err("trying to unpin a not attached buffer\n");
616 		return;
617 	}
618 
619 	if (WARN_ON(!sgt)) {
620 		pr_err("dmabuf buffer is already unpinned\n");
621 		return;
622 	}
623 
624 	if (buf->vaddr) {
625 		dma_buf_vunmap(buf->db_attach->dmabuf, buf->vaddr);
626 		buf->vaddr = NULL;
627 	}
628 	dma_buf_unmap_attachment(buf->db_attach, sgt, buf->dma_dir);
629 
630 	buf->dma_addr = 0;
631 	buf->dma_sgt = NULL;
632 }
633 
634 static void vb2_dc_detach_dmabuf(void *mem_priv)
635 {
636 	struct vb2_dc_buf *buf = mem_priv;
637 
638 	/* if vb2 works correctly you should never detach mapped buffer */
639 	if (WARN_ON(buf->dma_addr))
640 		vb2_dc_unmap_dmabuf(buf);
641 
642 	/* detach this attachment */
643 	dma_buf_detach(buf->db_attach->dmabuf, buf->db_attach);
644 	kfree(buf);
645 }
646 
647 static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
648 	unsigned long size, enum dma_data_direction dma_dir)
649 {
650 	struct vb2_dc_buf *buf;
651 	struct dma_buf_attachment *dba;
652 
653 	if (dbuf->size < size)
654 		return ERR_PTR(-EFAULT);
655 
656 	if (WARN_ON(!dev))
657 		return ERR_PTR(-EINVAL);
658 
659 	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
660 	if (!buf)
661 		return ERR_PTR(-ENOMEM);
662 
663 	buf->dev = dev;
664 	/* create attachment for the dmabuf with the user device */
665 	dba = dma_buf_attach(dbuf, buf->dev);
666 	if (IS_ERR(dba)) {
667 		pr_err("failed to attach dmabuf\n");
668 		kfree(buf);
669 		return dba;
670 	}
671 
672 	buf->dma_dir = dma_dir;
673 	buf->size = size;
674 	buf->db_attach = dba;
675 
676 	return buf;
677 }
678 
679 /*********************************************/
680 /*       DMA CONTIG exported functions       */
681 /*********************************************/
682 
683 const struct vb2_mem_ops vb2_dma_contig_memops = {
684 	.alloc		= vb2_dc_alloc,
685 	.put		= vb2_dc_put,
686 	.get_dmabuf	= vb2_dc_get_dmabuf,
687 	.cookie		= vb2_dc_cookie,
688 	.vaddr		= vb2_dc_vaddr,
689 	.mmap		= vb2_dc_mmap,
690 	.get_userptr	= vb2_dc_get_userptr,
691 	.put_userptr	= vb2_dc_put_userptr,
692 	.prepare	= vb2_dc_prepare,
693 	.finish		= vb2_dc_finish,
694 	.map_dmabuf	= vb2_dc_map_dmabuf,
695 	.unmap_dmabuf	= vb2_dc_unmap_dmabuf,
696 	.attach_dmabuf	= vb2_dc_attach_dmabuf,
697 	.detach_dmabuf	= vb2_dc_detach_dmabuf,
698 	.num_users	= vb2_dc_num_users,
699 };
700 EXPORT_SYMBOL_GPL(vb2_dma_contig_memops);
701 
702 /**
703  * vb2_dma_contig_set_max_seg_size() - configure DMA max segment size
704  * @dev:	device for configuring DMA parameters
705  * @size:	size of DMA max segment size to set
706  *
707  * To allow mapping the scatter-list into a single chunk in the DMA
708  * address space, the device is required to have the DMA max segment
709  * size parameter set to a value larger than the buffer size. Otherwise,
710  * the DMA-mapping subsystem will split the mapping into max segment
711  * size chunks. This function sets the DMA max segment size
712  * parameter to let DMA-mapping map a buffer as a single chunk in DMA
713  * address space.
714  * This code assumes that the DMA-mapping subsystem will merge all
715  * scatterlist segments if this is really possible (for example when
716  * an IOMMU is available and enabled).
717  * Ideally, this parameter should be set by the generic bus code, but it
718  * is left with the default 64KiB value due to historical litmiations in
719  * other subsystems (like limited USB host drivers) and there no good
720  * place to set it to the proper value.
721  * This function should be called from the drivers, which are known to
722  * operate on platforms with IOMMU and provide access to shared buffers
723  * (either USERPTR or DMABUF). This should be done before initializing
724  * videobuf2 queue.
725  */
726 int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size)
727 {
728 	if (!dev->dma_parms) {
729 		dev_err(dev, "Failed to set max_seg_size: dma_parms is NULL\n");
730 		return -ENODEV;
731 	}
732 	if (dma_get_max_seg_size(dev) < size)
733 		return dma_set_max_seg_size(dev, size);
734 
735 	return 0;
736 }
737 EXPORT_SYMBOL_GPL(vb2_dma_contig_set_max_seg_size);
738 
739 MODULE_DESCRIPTION("DMA-contig memory handling routines for videobuf2");
740 MODULE_AUTHOR("Pawel Osciak <pawel@osciak.com>");
741 MODULE_LICENSE("GPL");
742