[PATCH v14 02/56] media: videobuf2: Rework offset 'cookie' encoding pattern

Benjamin Gaignard
2023-10-31T16:31:35Z

Change how offset 'cookie' field value is computed to make possible
to use more buffers.
The maximum number of buffers depends of PAGE_SHIFT value and can
go up to 0x7fff when PAGE_SHIFT = 12.
With this encoding pattern we know the maximum number that a queue
could store so we can check it at queue init time.
It also make easier and faster to find buffer and plane from using
the offset field.
Change __find_plane_by_offset() prototype to return the video buffer
itself rather than it index.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
---
.../media/common/videobuf2/videobuf2-core.c | 73 +++++++++----------
1 file changed, 35 insertions(+), 38 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index a5e57affeb30..09be8e026044 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -31,6 +31,11 @@

#include <trace/events/vb2.h>

+#define PLANE_INDEX_SHIFT (PAGE_SHIFT + 3)
+#define PLANE_INDEX_MASK 0x7
+#define MAX_BUFFER_INDEX BIT_MASK(30 - PLANE_INDEX_SHIFT)
+#define BUFFER_INDEX_MASK (MAX_BUFFER_INDEX - 1)
+
static int debug;
module_param(debug, int, 0644);

@@ -358,21 +363,27 @@ static void __setup_offsets(struct vb2_buffer *vb)
unsigned int plane;
unsigned long offset = 0;

- if (vb->index) {
- struct vb2_buffer *prev = q->bufs[vb->index - 1];
- struct vb2_plane *p = &prev->planes[prev->num_planes - 1];
-
- offset = PAGE_ALIGN(p->m.offset + p->length);
- }
+ /*
+ * The offset "cookie" value has the following constraints:
+ * - a buffer can have up to 8 planes.
+ * - v4l2 mem2mem uses bit 30 to distinguish between
+ * OUTPUT (aka "source", bit 30 is 0) and
+ * CAPTURE (aka "destination", bit 30 is 1) buffers.
+ * - must be page aligned
+ * That led to this bit mapping when PAGE_SHIFT = 12:
+ * |30 |29 15|14 12|11 0|
+ * |DST_QUEUE_OFF_BASE|buffer index|plane index| 0 |
+ * where there are 15 bits to store the buffer index.
+ * Depending on PAGE_SHIFT value we can have fewer bits
+ * to store the buffer index.
+ */
+ offset = vb->index << PLANE_INDEX_SHIFT;

for (plane = 0; plane < vb->num_planes; ++plane) {
- vb->planes[plane].m.offset = offset;
+ vb->planes[plane].m.offset = offset + (plane << PAGE_SHIFT);

dprintk(q, 3, "buffer %d, plane %d offset 0x%08lx\n",
vb->index, plane, offset);
-
- offset += vb->planes[plane].length;
- offset = PAGE_ALIGN(offset);
}
}

@@ -2188,10 +2199,9 @@ EXPORT_SYMBOL_GPL(vb2_core_streamoff);
* __find_plane_by_offset() - find plane associated with the given offset
*/
static int __find_plane_by_offset(struct vb2_queue *q, unsigned long offset,
- unsigned int *_buffer, unsigned int *_plane)
+ struct vb2_buffer **vb, unsigned int *plane)
{
- struct vb2_buffer *vb;
- unsigned int buffer, plane;
+ unsigned int buffer;

/*
* Sanity checks to ensure the lock is held, MEMORY_MMAP is
@@ -2209,24 +2219,15 @@ static int __find_plane_by_offset(struct vb2_queue *q, unsigned long offset,
return -EBUSY;
}

- /*
- * Go over all buffers and their planes, comparing the given offset
- * with an offset assigned to each plane. If a match is found,
- * return its buffer and plane numbers.
- */
- for (buffer = 0; buffer < q->num_buffers; ++buffer) {
- vb = q->bufs[buffer];
+ /* Get buffer and plane from the offset */
+ buffer = (offset >> PLANE_INDEX_SHIFT) & BUFFER_INDEX_MASK;
+ *plane = (offset >> PAGE_SHIFT) & PLANE_INDEX_MASK;

- for (plane = 0; plane < vb->num_planes; ++plane) {
- if (vb->planes[plane].m.offset == offset) {
- *_buffer = buffer;
- *_plane = plane;
- return 0;
- }
- }
- }
+ if (buffer >= q->num_buffers || *plane >= q->bufs[buffer]->num_planes)
+ return -EINVAL;

- return -EINVAL;
+ *vb = q->bufs[buffer];
+ return 0;
}

int vb2_core_expbuf(struct vb2_queue *q, int *fd, unsigned int type,
@@ -2306,7 +2307,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
{
unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
struct vb2_buffer *vb;
- unsigned int buffer = 0, plane = 0;
+ unsigned int plane = 0;
int ret;
unsigned long length;

@@ -2335,12 +2336,10 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
* Find the plane corresponding to the offset passed by userspace. This
* will return an error if not MEMORY_MMAP or file I/O is in progress.
*/
- ret = __find_plane_by_offset(q, offset, &buffer, &plane);
+ ret = __find_plane_by_offset(q, offset, &vb, &plane);
if (ret)
goto unlock;

- vb = q->bufs[buffer];
-
/*
* MMAP requires page_aligned buffers.
* The buffer length was page_aligned at __vb2_buf_mem_alloc(),
@@ -2368,7 +2367,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
if (ret)
return ret;

- dprintk(q, 3, "buffer %d, plane %d successfully mapped\n", buffer, plane);
+ dprintk(q, 3, "buffer %u, plane %d successfully mapped\n", vb->index, plane);
return 0;
}
EXPORT_SYMBOL_GPL(vb2_mmap);
@@ -2382,7 +2381,7 @@ unsigned long vb2_get_unmapped_area(struct vb2_queue *q,
{
unsigned long offset = pgoff << PAGE_SHIFT;
struct vb2_buffer *vb;
- unsigned int buffer, plane;
+ unsigned int plane;
void *vaddr;
int ret;

@@ -2392,12 +2391,10 @@ unsigned long vb2_get_unmapped_area(struct vb2_queue *q,
* Find the plane corresponding to the offset passed by userspace. This
* will return an error if not MEMORY_MMAP or file I/O is in progress.
*/
- ret = __find_plane_by_offset(q, offset, &buffer, &plane);
+ ret = __find_plane_by_offset(q, offset, &vb, &plane);
if (ret)
goto unlock;

- vb = q->bufs[buffer];
-
vaddr = vb2_plane_vaddr(vb, plane);
mutex_unlock(&q->mmap_lock);
return vaddr ? (unsigned long)vaddr : -EINVAL;
--
2.39.2