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Message-ID: <08636b49-9022-4361-96d2-574de2548ab0@xs4all.nl>
Date: Mon, 2 Oct 2023 15:46:07 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>,
mchehab@...nel.org, tfiga@...omium.org, m.szyprowski@...sung.com,
ming.qian@....com, ezequiel@...guardiasur.com.ar,
p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
nicolas.dufresne@...labora.com
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
kernel@...labora.com
Subject: Re: [PATCH v9 01/53] media: videobuf2: Rework offset 'cookie'
encoding pattern
On 02/10/2023 14:05, 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@...labora.com>
> ---
> changes in version 9:
> - BUFFER_INDEX_MASK now depends on PAGE_SHIFT value to match
> architectures requirements.
>
> .../media/common/videobuf2/videobuf2-core.c | 71 +++++++++----------
> 1 file changed, 32 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index cf6727d9c81f..a0540b2e461f 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -31,6 +31,10 @@
>
> #include <trace/events/vb2.h>
>
> +#define PLANE_INDEX_SHIFT (PAGE_SHIFT + 3)
> +#define PLANE_INDEX_MASK 0x7
> +#define BUFFER_INDEX_MASK (BIT_MASK(30 - PLANE_INDEX_SHIFT) - 1)
> +
> static int debug;
> module_param(debug, int, 0644);
>
> @@ -358,21 +362,24 @@ 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 could have up to 8 planes.
could -> can
> + * - v4l2 mem2mem use bit 30 to distinguish between source and destination buffers.
use -> uses
> + * - 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 buffer index.
buffer index -> the buffer index
> + * Depending on PAGE_SHIFT value we can have else bits to store buffer index.
else bits? You probably mean "fewer bits".
buffer index -> the 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);
> }
> }
Regards,
Hans
>
> @@ -2185,13 +2192,12 @@ 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 +2215,15 @@ 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 +2303,7 @@ 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 +2332,10 @@ 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 +2363,7 @@ 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 +2377,7 @@ 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 +2387,10 @@ 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;
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