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    SubjectRe: [PATCH v10 01/54] media: videobuf2: Rework offset 'cookie' encoding pattern
    Hi Benjamin,

    On Tue, Oct 03, 2023 at 10:06:10AM +0200, Benjamin Gaignard wrote:
    > 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>
    > ---
    > changes in version 10:
    > - Make BUFFER_INDEX_MASK definition more readable.
    > - Correct typo.
    >
    > .../media/common/videobuf2/videobuf2-core.c | 72 +++++++++----------
    > 1 file changed, 33 insertions(+), 39 deletions(-)
    >
    > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
    > index 27aee92f3eea..5591ac830668 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 +363,24 @@ 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 can have up to 8 planes.
    > + * - v4l2 mem2mem uses bit 30 to distinguish between source and destination buffers.

    Long line.

    Shouldn't this be OUTPUT and CAPTURE?

    > + * - 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.

    Here, too...

    > + */
    > + 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 +2193,12 @@ 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 +2216,15 @@ 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 +2304,7 @@ 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 +2333,10 @@ 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 +2364,7 @@ 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 +2378,7 @@ 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 +2388,10 @@ 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;

    --
    Regards,

    Sakari Ailus

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