media: vb2: Fix a bug about unnecessary calls to queue cancel and free

Currently, there's a logic with checks if *count is non-zero,
q->num_buffers is zero and q->memory is different than memory.

That's flawed when the device is initialized, or after the
queues are freed, as it does, unnecessary calls to
__vb2_queue_cancel() and  __vb2_queue_free().

That can be avoided by making sure that q->memory is set to
VB2_MEMORY_UNKNOWN at vb2_core_queue_init(), and adding such
check at the loop.

[mchehab@s-opensource.com: fix checkpatch issues and improve the
 patch, by setting q->memory to zero at vb2_core_queue_init]

Signed-off-by: Satendra Singh Thakur <satendra.t@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/common/videobuf/videobuf2-core.c

@@ -524,7 +524,7 @@ static int __vb2_queue_free(struct vb2_queue *q, unsigned int buffers)
 
 	q->num_buffers -= buffers;
 	if (!q->num_buffers) {
-		q->memory = 0;
+		q->memory = VB2_MEMORY_UNKNOWN;
 		INIT_LIST_HEAD(&q->queued_list);
 	}
 	return 0;
@@ -666,7 +666,8 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
 		return -EBUSY;
 	}
 
-	if (*count == 0 || q->num_buffers != 0 || q->memory != memory) {
+	if (*count == 0 || q->num_buffers != 0 ||
+	    (q->memory != VB2_MEMORY_UNKNOWN && q->memory != memory)) {
 		/*
 		 * We already have buffers allocated, so first check if they
 		 * are not in use and can be freed.
@@ -1999,6 +2000,8 @@ int vb2_core_queue_init(struct vb2_queue *q)
 	mutex_init(&q->mmap_lock);
 	init_waitqueue_head(&q->done_wq);
 
+	q->memory = VB2_MEMORY_UNKNOWN;
+
 	if (q->buf_struct_size == 0)
 		q->buf_struct_size = sizeof(struct vb2_buffer);