[PATCH v6 01/18] media: videobuf2: Rework offset 'cookie' encoding pattern

[Benjamin Gaignard]

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 at collabora.com>
---
v6:
- Change buffer index name to BUFFER_INDEX_MASK
- Max size if 0x7fff not 0xffff

 .../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
+
 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.
+	 */
+	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);
 	}
 }
 
@@ -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];
+	if (vb->planes[plane].m.offset == off) {
+		*_buffer = buffer;
+		*_plane = plane;
+		return 0;
 	}
 
 	return -EINVAL;
-- 
2.39.2