Re: [PATCH v5 01/10] media: videobuf2: Rework offset 'cookie' encoding pattern
From: Benjamin Gaignard
Date: Wed Aug 30 2023 - 15:15:05 EST
Le 30/08/2023 à 14:25, Hans Verkuil a écrit :
On 24/08/2023 11:21, Benjamin Gaignard wrote:
Change how offset 'cookie' field value is computed to make possible
to use more buffers (up to 0xffff).
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>
---
v5:
- I haven't change DST_QUEUE_OFF_BASE definition because it used in
v4l2-mem2mem and s5p_mfc driver with a shift.
.../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..e06905533ef4 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
Very poor name, see below.
+
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 16 bits to store buffer index.
16 -> 15: there are 15 (not 16!) bits available for buffer indices. So the maximum
number of buffers is 32768, given that the indices start at 0.
+ */
+ 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);
}
}
@@ -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 + PAGE_SHIFT)) & MAX_BUFFERS;
Hmm, you use it as a mask. The name MAX_BUFFERS is really confusing.
How about BUFFER_INDEX_MASK? That is consistent with PLANE_INDEX_MASK.
I will follow your advice and fix that in next version.
I will until you have finish your review in this series before send it.
Regards,
Benjamin
+ 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;
Regards,
Hans