[PATCH v12 02/56] media: videobuf2: Rework offset 'cookie' encoding pattern

[Benjamin Gaignard]

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@xxxxxxxxxxxxx>
---
 .../media/common/videobuf2/videobuf2-core.c   | 73 +++++++++----------
 1 file changed, 35 insertions(+), 38 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index a5e57affeb30..09be8e026044 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -31,6 +31,11 @@
 
 #include <trace/events/vb2.h>
 
+#define PLANE_INDEX_SHIFT	(PAGE_SHIFT + 3)
+#define PLANE_INDEX_MASK	0x7
+#define MAX_BUFFER_INDEX	BIT_MASK(30 - PLANE_INDEX_SHIFT)
+#define BUFFER_INDEX_MASK	(MAX_BUFFER_INDEX - 1)
+
 static int debug;
 module_param(debug, int, 0644);
 
@@ -358,21 +363,27 @@ static void __setup_offsets(struct vb2_buffer *vb)
 	unsigned int plane;
 	unsigned long offset = 0;
 
-	if (vb->index) {
-		struct vb2_buffer *prev = q->bufs[vb->index - 1];
-		struct vb2_plane *p = &prev->planes[prev->num_planes - 1];
-
-		offset = PAGE_ALIGN(p->m.offset + p->length);
-	}
+	/*
+	 * The offset "cookie" value has the following constraints:
+	 * - a buffer can have up to 8 planes.
+	 * - v4l2 mem2mem uses bit 30 to distinguish between
+	 *   OUTPUT (aka "source", bit 30 is 0) and
+	 *   CAPTURE (aka "destination", bit 30 is 1) buffers.
+	 * - 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 the buffer index.
+	 * Depending on PAGE_SHIFT value we can have fewer bits
+	 * to store the buffer index.
+	 */
+	offset = vb->index << PLANE_INDEX_SHIFT;
 
 	for (plane = 0; plane < vb->num_planes; ++plane) {
-		vb->planes[plane].m.offset = offset;
+		vb->planes[plane].m.offset = offset + (plane << PAGE_SHIFT);
 
 		dprintk(q, 3, "buffer %d, plane %d offset 0x%08lx\n",
 				vb->index, plane, offset);
-
-		offset += vb->planes[plane].length;
-		offset = PAGE_ALIGN(offset);
 	}
 }
 
@@ -2188,10 +2199,9 @@ EXPORT_SYMBOL_GPL(vb2_core_streamoff);
  * __find_plane_by_offset() - find plane associated with the given offset
  */
 static int __find_plane_by_offset(struct vb2_queue *q, unsigned long offset,
-			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 +2219,15 @@ static int __find_plane_by_offset(struct vb2_queue *q, unsigned long offset,
 		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 = (offset >> PLANE_INDEX_SHIFT) & BUFFER_INDEX_MASK;
+	*plane = (offset >> PAGE_SHIFT) & PLANE_INDEX_MASK;
 
-		for (plane = 0; plane < vb->num_planes; ++plane) {
-			if (vb->planes[plane].m.offset == offset) {
-				*_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 +2307,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
 {
 	unsigned long offset = 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 +2336,10 @@ 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, offset, &buffer, &plane);
+	ret = __find_plane_by_offset(q, offset, &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 +2367,7 @@ 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 +2381,7 @@ unsigned long vb2_get_unmapped_area(struct vb2_queue *q,
 {
 	unsigned long offset = pgoff << PAGE_SHIFT;
 	struct vb2_buffer *vb;
-	unsigned int buffer, plane;
+	unsigned int plane;
 	void *vaddr;
 	int ret;
 
@@ -2392,12 +2391,10 @@ 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, offset, &buffer, &plane);
+	ret = __find_plane_by_offset(q, offset, &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;
-- 
2.39.2