[v7,01/49] media: videobuf2: Rework offset 'cookie' encoding pattern

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.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
---
 .../media/common/videobuf2/videobuf2-core.c   | 48 +++++++++----------
 1 file changed, 24 insertions(+), 24 deletions(-)

On 14/09/2023 15:32, 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.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
> ---
>  .../media/common/videobuf2/videobuf2-core.c   | 48 +++++++++----------
>  1 file changed, 24 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index cf6727d9c81f..cf3b9f5b69b7 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	0x7fff

It's a bit paranoid, but I would like to add a check for PAGE_SHIFT here:

#if PAGE_SHIFT != 12
#error Expected PAGE_SHIFT to be 12
#endif

Things will go very wrong if this value ever changes...

> +
>  static int debug;
>  module_param(debug, int, 0644);
>  
> @@ -358,21 +362,23 @@ 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 is 15 bits to store buffer index.

typo: is -> are

> +	 */
> +	off = vb->index << (PLANE_INDEX_SHIFT);

No need for ().

>  
>  	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);
>  	}
>  }
>  
> @@ -2209,21 +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;
> -			}
> -		}
> +	vb = q->bufs[buffer];

Hmm, shouldn't there be a sanity check for the buffer value?

> +	if (vb->planes[plane].m.offset == off) {

Does this check make sense?

> +		*_buffer = buffer;
> +		*_plane = plane;
> +		return 0;
>  	}
>  
>  	return -EINVAL;

How about this:

	/* Get buffer and plane from the offset */
	*buffer = (off >> PLANE_INDEX_SHIFT) & BUFFER_INDEX_MASK;
	*plane = (off >> PAGE_SHIFT) & PLANE_INDEX_MASK;

	if (*buffer >= q->num_buffers || *plane >= q->bufs[buffer]->num_planes)
		return -EINVAL;
	return 0;

Regards,

	Hans