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

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

diff --git a/drivers/media/video/videobuf-dma-sg.c b/drivers/media/video/videobuf-dma-sg.c
index 717783f..e6ce99f 100644 (file)
--- 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;