[PATCH v4 03/10] media: videobuf2: Rework offset 'cookie' encoding pattern

[Benjamin Gaignard]

Change how offset 'cookie' field value is computed to make possible
to use more buffers.
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@xxxxxxxxxxxxx>
---
 .../media/common/videobuf2/videobuf2-core.c   | 63 +++++++++----------
 1 file changed, 29 insertions(+), 34 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index 77e69b01d88d..70e36389b704 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	3
+#define PLANE_INDEX_MASK	0x7
+#define MAX_BUFFERS		0xffff
+
 static int debug;
 module_param(debug, int, 0644);
 
@@ -358,29 +362,23 @@ static void __setup_offsets(struct vb2_buffer *vb)
 	unsigned int plane;
 	unsigned long off = 0;
 
-	if (vb->index) {
-		struct vb2_buffer *prev;
-		struct vb2_plane *p;
-
-		prev = vb2_get_buffer(q, vb->index - 1);
-		if (!prev) {
-			dprintk(q, 1, "can't find the requested buffer\n");
-			return;
-		}
-
-		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 16 bits to store buffer index.
+	 */
+	off = vb->index << (PLANE_INDEX_SHIFT + PAGE_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);
 	}
 }
 
@@ -2294,24 +2292,18 @@ 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 = vb2_get_buffer(q, buffer);
+	/* Get buffer and plane from the offset */
+	buffer = (off >> (PLANE_INDEX_SHIFT + PAGE_SHIFT)) & MAX_BUFFERS;
+	plane = (off >> PAGE_SHIFT) & PLANE_INDEX_MASK;
 
-		if (!vb)
-			continue;
+	vb = vb2_get_buffer(q, buffer);
+	if (!vb)
+		return -EINVAL;
 
-		for (plane = 0; plane < vb->num_planes; ++plane) {
-			if (vb->planes[plane].m.offset == off) {
-				*_buffer = buffer;
-				*_plane = plane;
-				return 0;
-			}
-		}
+	if (vb->planes[plane].m.offset == off) {
+		*_buffer = buffer;
+		*_plane = plane;
+		return 0;
 	}
 
 	return -EINVAL;
@@ -2552,6 +2544,9 @@ int vb2_core_queue_init(struct vb2_queue *q)
 	if (!q->max_allowed_buffers)
 		q->max_allowed_buffers = VB2_MAX_FRAME;
 
+	/* The maximum is limited by offset cookie encoding pattern */
+	q->max_allowed_buffers = min_t(unsigned int, q->max_allowed_buffers, MAX_BUFFERS);
+
 	q->bufs = kcalloc(q->max_allowed_buffers, sizeof(*q->bufs), GFP_KERNEL);
 
 	if (q->buf_struct_size == 0)
-- 
2.39.2