BCM2835_MBOX_TAG_VAL_LEN_RESPONSE
tag->val_len = BCM2835_MBOX_TAG_VAL_LEN_RESPONSE |
if ((tag->val_len & BCM2835_MBOX_TAG_VAL_LEN_RESPONSE) == 0) {
tag->val_len &= ~BCM2835_MBOX_TAG_VAL_LEN_RESPONSE;