drivers/media/common/videobuf2/frame_vector.c

Source file repositories/reference/linux-study-clean/drivers/media/common/videobuf2/frame_vector.c

File Facts

System
Linux kernel
Corpus path
drivers/media/common/videobuf2/frame_vector.c
Extension
.c
Size
5541 bytes
Lines
198
Domain
Driver Families
Bucket
drivers/media
Inferred role
Driver Families: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/pagemap.h>
#include <linux/sched.h>

#include <media/frame_vector.h>

/**
 * get_vaddr_frames() - map virtual addresses to pfns
 * @start:	starting user address
 * @nr_frames:	number of pages / pfns from start to map
 * @write:	the mapped address has write permission
 * @vec:	structure which receives pages / pfns of the addresses mapped.
 *		It should have space for at least nr_frames entries.
 *
 * This function maps virtual addresses from @start and fills @vec structure
 * with page frame numbers or page pointers to corresponding pages (choice
 * depends on the type of the vma underlying the virtual address). If @start
 * belongs to a normal vma, the function grabs reference to each of the pages
 * to pin them in memory. If @start belongs to VM_IO | VM_PFNMAP vma, we don't
 * touch page structures and the caller must make sure pfns aren't reused for
 * anything else while he is using them.
 *
 * The function returns number of pages mapped which may be less than
 * @nr_frames. In particular we stop mapping if there are more vmas of
 * different type underlying the specified range of virtual addresses.
 * When the function isn't able to map a single page, it returns error.
 *
 * Note that get_vaddr_frames() cannot follow VM_IO mappings. It used
 * to be able to do that, but that could (racily) return non-refcounted
 * pfns.
 *
 * This function takes care of grabbing mmap_lock as necessary.
 */
int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
		     struct frame_vector *vec)
{
	int ret;
	unsigned int gup_flags = FOLL_LONGTERM;

	if (nr_frames == 0)
		return 0;

	if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
		nr_frames = vec->nr_allocated;

	start = untagged_addr(start);

	if (write)
		gup_flags |= FOLL_WRITE;

	ret = pin_user_pages_fast(start, nr_frames, gup_flags,
				  (struct page **)(vec->ptrs));
	vec->got_ref = true;
	vec->is_pfns = false;
	vec->nr_frames = ret;

	if (likely(ret > 0))
		return ret;

	vec->nr_frames = 0;
	return ret ? ret : -EFAULT;
}
EXPORT_SYMBOL(get_vaddr_frames);

/**
 * put_vaddr_frames() - drop references to pages if get_vaddr_frames() acquired
 *			them
 * @vec:	frame vector to put
 *
 * Drop references to pages if get_vaddr_frames() acquired them. We also
 * invalidate the frame vector so that it is prepared for the next call into
 * get_vaddr_frames().
 */
void put_vaddr_frames(struct frame_vector *vec)
{
	struct page **pages;

	if (!vec->got_ref)
		goto out;
	pages = frame_vector_pages(vec);
	/*
	 * frame_vector_pages() might needed to do a conversion when
	 * get_vaddr_frames() got pages but vec was later converted to pfns.
	 * But it shouldn't really fail to convert pfns back...

Annotation

Implementation Notes