[media] v4l2-mem2mem: add support for prepare_buf

This was never added for some reason, so add it now.

Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/v4l2-core/v4l2-mem2mem.c

···
 EXPORT_SYMBOL_GPL(v4l2_m2m_dqbuf);
 
 /**
+ * v4l2_m2m_prepare_buf() - prepare a source or destination buffer, depending on
+ * the type
+ */
+int v4l2_m2m_prepare_buf(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
+			 struct v4l2_buffer *buf)
+{
+	struct vb2_queue *vq;
+	int ret;
+
+	vq = v4l2_m2m_get_vq(m2m_ctx, buf->type);
+	ret = vb2_prepare_buf(vq, buf);
+	if (!ret)
+		v4l2_m2m_try_schedule(m2m_ctx);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(v4l2_m2m_prepare_buf);
+
+/**
  * v4l2_m2m_create_bufs() - create a source or destination buffer, depending
  * on the type
  */
···
 	return v4l2_m2m_dqbuf(file, fh->m2m_ctx, buf);
 }
 EXPORT_SYMBOL_GPL(v4l2_m2m_ioctl_dqbuf);
+
+int v4l2_m2m_ioctl_prepare_buf(struct file *file, void *priv,
+			       struct v4l2_buffer *buf)
+{
+	struct v4l2_fh *fh = file->private_data;
+
+	return v4l2_m2m_prepare_buf(file, fh->m2m_ctx, buf);
+}
+EXPORT_SYMBOL_GPL(v4l2_m2m_ioctl_prepare_buf);
 
 int v4l2_m2m_ioctl_expbuf(struct file *file, void *priv,
 				struct v4l2_exportbuffer *eb)

include/media/v4l2-mem2mem.h

···
 		  struct v4l2_buffer *buf);
 int v4l2_m2m_dqbuf(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
 		   struct v4l2_buffer *buf);
+int v4l2_m2m_prepare_buf(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
+			 struct v4l2_buffer *buf);
 int v4l2_m2m_create_bufs(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
 			 struct v4l2_create_buffers *create);
 
···
 				struct v4l2_buffer *buf);
 int v4l2_m2m_ioctl_dqbuf(struct file *file, void *fh,
 				struct v4l2_buffer *buf);
+int v4l2_m2m_ioctl_prepare_buf(struct file *file, void *fh,
+			       struct v4l2_buffer *buf);
 int v4l2_m2m_ioctl_streamon(struct file *file, void *fh,
 				enum v4l2_buf_type type);
 int v4l2_m2m_ioctl_streamoff(struct file *file, void *fh,