V4L/DVB (7494): videobuf-dma-sg.c: Avoid NULL dereference and add comment about backwards compatibility

Signed-off-by: Brandon Philips <bphilips@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/drivers/media/video/videobuf-dma-sg.c b/drivers/media/video/videobuf-dma-sg.c
index 717783fa8b3e..e6ce99ff7fd1 100644
--- a/drivers/media/video/videobuf-dma-sg.c
+++ b/drivers/media/video/videobuf-dma-sg.c
@@ -546,6 +546,14 @@ static int __videobuf_mmap_mapper(struct videobuf_queue *q,
                 goto done;
         }
 
+        /* This function maintains backwards compatibility with V4L1 and will
+         * map more than one buffer if the vma length is equal to the combined
+         * size of multiple buffers than it will map them together.  See
+         * VIDIOCGMBUF in the v4l spec
+         *
+         * TODO: Allow drivers to specify if they support this mode
+         */
+
         /* look for first buffer to map */
         for (first = 0; first < VIDEO_MAX_FRAME; first++) {
                 if (NULL == q->bufs[first])
@@ -590,10 +598,16 @@ static int __videobuf_mmap_mapper(struct videobuf_queue *q,
         map = kmalloc(sizeof(struct videobuf_mapping),GFP_KERNEL);
         if (NULL == map)
                 goto done;
-        for (size = 0, i = first; i <= last; size += q->bufs[i++]->bsize) {
+
+        size = 0;
+        for (i = first; i <= last; i++) {
+                if (NULL == q->bufs[i])
+                        continue;
                 q->bufs[i]->map   = map;
                 q->bufs[i]->baddr = vma->vm_start + size;
+                size += q->bufs[i]->bsize;
         }
+
         map->count    = 1;
         map->start    = vma->vm_start;
         map->end      = vma->vm_end;