static int set_txreq_header(struct user_sdma_request *req,
			    struct user_sdma_txreq *tx, u32 datalen)
{
	struct hfi1_user_sdma_pkt_q *pq = req->pq;
	struct hfi1_pkt_header *hdr = &tx->hdr;
	u8 omfactor; /* KDETH.OM */
	u16 pbclen;
	int ret;
	u32 tidval = 0, lrhlen = get_lrh_len(*hdr, pad_len(datalen));

	/* Copy the header template to the request before modification */
	memcpy(hdr, &req->hdr, sizeof(*hdr));

	/*
	 * Check if the PBC and LRH length are mismatched. If so
	 * adjust both in the header.
	 */
	pbclen = le16_to_cpu(hdr->pbc[0]);
	if (PBC2LRH(pbclen) != lrhlen) {
		pbclen = (pbclen & 0xf000) | LRH2PBC(lrhlen);
		hdr->pbc[0] = cpu_to_le16(pbclen);
		hdr->lrh[2] = cpu_to_be16(lrhlen >> 2);
		/*
		 * Third packet
		 * This is the first packet in the sequence that has
		 * a "static" size that can be used for the rest of
		 * the packets (besides the last one).
		 */
		if (unlikely(req->seqnum == 2)) {
			/*
			 * From this point on the lengths in both the
			 * PBC and LRH are the same until the last
			 * packet.
			 * Adjust the template so we don't have to update
			 * every packet
			 */
			req->hdr.pbc[0] = hdr->pbc[0];
			req->hdr.lrh[2] = hdr->lrh[2];
		}
	}
	/*
	 * We only have to modify the header if this is not the
	 * first packet in the request. Otherwise, we use the
	 * header given to us.
	 */
	if (unlikely(!req->seqnum)) {
		ret = check_header_template(req, hdr, lrhlen, datalen);
		if (ret)
			return ret;
		goto done;
	}

	hdr->bth[2] = cpu_to_be32(
		set_pkt_bth_psn(hdr->bth[2],
				(req_opcode(req->info.ctrl) == EXPECTED),
				req->seqnum));

	/* Set ACK request on last packet */
	if (unlikely(tx->flags & TXREQ_FLAGS_REQ_ACK))
		hdr->bth[2] |= cpu_to_be32(1UL << 31);

	/* Set the new offset */
	hdr->kdeth.swdata[6] = cpu_to_le32(req->koffset);
	/* Expected packets have to fill in the new TID information */
	if (req_opcode(req->info.ctrl) == EXPECTED) {
		tidval = req->tids[req->tididx];
		/*
		 * If the offset puts us at the end of the current TID,
		 * advance everything.
		 */
		if ((req->tidoffset) == (EXP_TID_GET(tidval, LEN) *
					 PAGE_SIZE)) {
			req->tidoffset = 0;
			/*
			 * Since we don't copy all the TIDs, all at once,
			 * we have to check again.
			 */
			if (++req->tididx > req->n_tids - 1 ||
			    !req->tids[req->tididx]) {
				return -EINVAL;
			}
			tidval = req->tids[req->tididx];
		}
		omfactor = EXP_TID_GET(tidval, LEN) * PAGE_SIZE >=
			KDETH_OM_MAX_SIZE ? KDETH_OM_LARGE_SHIFT :
			KDETH_OM_SMALL_SHIFT;
		/* Set KDETH.TIDCtrl based on value for this TID. */
		KDETH_SET(hdr->kdeth.ver_tid_offset, TIDCTRL,
			  EXP_TID_GET(tidval, CTRL));
		/* Set KDETH.TID based on value for this TID */
		KDETH_SET(hdr->kdeth.ver_tid_offset, TID,
			  EXP_TID_GET(tidval, IDX));
		/* Clear KDETH.SH when DISABLE_SH flag is set */
		if (unlikely(tx->flags & TXREQ_FLAGS_REQ_DISABLE_SH))
			KDETH_SET(hdr->kdeth.ver_tid_offset, SH, 0);
		/*
		 * Set the KDETH.OFFSET and KDETH.OM based on size of
		 * transfer.
		 */
		trace_hfi1_sdma_user_tid_info(
			pq->dd, pq->ctxt, pq->subctxt, req->info.comp_idx,
			req->tidoffset, req->tidoffset >> omfactor,
			omfactor != KDETH_OM_SMALL_SHIFT);
		KDETH_SET(hdr->kdeth.ver_tid_offset, OFFSET,
			  req->tidoffset >> omfactor);
		KDETH_SET(hdr->kdeth.ver_tid_offset, OM,
			  omfactor != KDETH_OM_SMALL_SHIFT);
	}
done:
	trace_hfi1_sdma_user_header(pq->dd, pq->ctxt, pq->subctxt,
				    req->info.comp_idx, hdr, tidval);
	return sdma_txadd_kvaddr(pq->dd, &tx->txreq, hdr, sizeof(*hdr));
}