On 27/09/2023 17:35, Benjamin Gaignard wrote:
> Change how offset 'cookie' field value is computed to make possible
> to use more buffers (up to 0x7fff)
> With this encoding pattern we know the maximum number that a queue
> could store so we can check ing 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 | 74 +++++++++----------
> 1 file changed, 35 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index cf6727d9c81f..6eeddb3a01c7 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -31,6 +31,14 @@
>
> #include <trace/events/vb2.h>
>
> +#define PLANE_INDEX_SHIFT (PAGE_SHIFT + 3)
> +#define PLANE_INDEX_MASK 0x7
> +#define BUFFER_INDEX_MASK 0x7fff
> +
> +#if PAGE_SHIFT != 12
> +#error Expected PAGE_SHIFT to be 12
So it turns out this can actually be something other than 12.
Search for CONFIG_ARM64_PAGE_SHIFT and CONFIG_PPC_PAGE_SHIFT.
arm64 supports 12, 14, 16 and powerpc64 supports 12, 14, 16, 18.
I think we should calculate the BUFFER_INDEX_MASK based on the
PAGE_SHIFT value. Even with a PAGE_SHIFT of 18, you can still
allocate up to 512 buffers.
Regards,
Hans
@@ -31,6 +31,14 @@
#include <trace/events/vb2.h>
+#define PLANE_INDEX_SHIFT (PAGE_SHIFT + 3)
+#define PLANE_INDEX_MASK 0x7
+#define BUFFER_INDEX_MASK 0x7fff
+
+#if PAGE_SHIFT != 12
+#error Expected PAGE_SHIFT to be 12
+#endif
+
static int debug;
module_param(debug, int, 0644);
@@ -358,21 +366,23 @@ static void __setup_offsets(struct vb2_buffer *vb)
unsigned int plane;
unsigned long off = 0;
- if (vb->index) {
- struct vb2_buffer *prev = q->bufs[vb->index - 1];
- struct vb2_plane *p = &prev->planes[prev->num_planes - 1];
-
- off = PAGE_ALIGN(p->m.offset + p->length);
- }
+ /*
+ * Offsets cookies value have the following constraints:
+ * - a buffer could have up to 8 planes.
+ * - v4l2 mem2mem use bit 30 to distinguish between source and destination buffers.
+ * - must be page aligned
+ * That led to this bit mapping:
+ * |30 |29 15|14 12|11 0|
+ * |DST_QUEUE_OFF_BASE|buffer index|plane index| 0 |
+ * where there are 15 bits to store buffer index.
+ */
+ off = vb->index << PLANE_INDEX_SHIFT;
for (plane = 0; plane < vb->num_planes; ++plane) {
- vb->planes[plane].m.offset = off;
+ vb->planes[plane].m.offset = off + (plane << PAGE_SHIFT);
dprintk(q, 3, "buffer %d, plane %d offset 0x%08lx\n",
vb->index, plane, off);
-
- off += vb->planes[plane].length;
- off = PAGE_ALIGN(off);
}
}
@@ -2185,13 +2195,12 @@ int vb2_core_streamoff(struct vb2_queue *q, unsigned int type)
EXPORT_SYMBOL_GPL(vb2_core_streamoff);
/*
- * __find_plane_by_offset() - find plane associated with the given offset off
+ * __find_plane_by_offset() - find video buffer and plane associated with the given offset off
*/
static int __find_plane_by_offset(struct vb2_queue *q, unsigned long off,
- 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 +2218,15 @@ static int __find_plane_by_offset(struct vb2_queue *q, unsigned long off,
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 = (off >> PLANE_INDEX_SHIFT) & BUFFER_INDEX_MASK;
+ *plane = (off >> PAGE_SHIFT) & PLANE_INDEX_MASK;
- for (plane = 0; plane < vb->num_planes; ++plane) {
- if (vb->planes[plane].m.offset == off) {
- *_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 +2306,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
{
unsigned long off = 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 +2335,10 @@ 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, off, &buffer, &plane);
+ ret = __find_plane_by_offset(q, off, &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 +2366,7 @@ 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 +2380,7 @@ unsigned long vb2_get_unmapped_area(struct vb2_queue *q,
{
unsigned long off = pgoff << PAGE_SHIFT;
struct vb2_buffer *vb;
- unsigned int buffer, plane;
+ unsigned int plane;
void *vaddr;
int ret;
@@ -2392,12 +2390,10 @@ 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, off, &buffer, &plane);
+ ret = __find_plane_by_offset(q, off, &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;