+static unsigned int
+sfc_ef10_tx_pkt_descs_max(const struct rte_mbuf *m)
+{
+ unsigned int extra_descs_per_seg;
+ unsigned int extra_descs_per_pkt;
+
+ /*
+ * VLAN offload is not supported yet, so no extra descriptors
+ * are required for VLAN option descriptor.
+ */
+
+/** Maximum length of the mbuf segment data */
+#define SFC_MBUF_SEG_LEN_MAX UINT16_MAX
+ RTE_BUILD_BUG_ON(sizeof(m->data_len) != 2);
+
+ /*
+ * Each segment is already counted once below. So, calculate
+ * how many extra DMA descriptors may be required per segment in
+ * the worst case because of maximum DMA descriptor length limit.
+ * If maximum segment length is less or equal to maximum DMA
+ * descriptor length, no extra DMA descriptors are required.
+ */
+ extra_descs_per_seg =
+ (SFC_MBUF_SEG_LEN_MAX - 1) / SFC_EF10_TX_DMA_DESC_LEN_MAX;
+
+/** Maximum length of the packet */
+#define SFC_MBUF_PKT_LEN_MAX UINT32_MAX
+ RTE_BUILD_BUG_ON(sizeof(m->pkt_len) != 4);
+
+ /*
+ * One more limitation on maximum number of extra DMA descriptors
+ * comes from slicing entire packet because of DMA descriptor length
+ * limit taking into account that there is at least one segment
+ * which is already counted below (so division of the maximum
+ * packet length minus one with round down).
+ * TSO is not supported yet, so packet length is limited by
+ * maximum PDU size.
+ */
+ extra_descs_per_pkt =
+ (RTE_MIN((unsigned int)EFX_MAC_PDU_MAX,
+ SFC_MBUF_PKT_LEN_MAX) - 1) /
+ SFC_EF10_TX_DMA_DESC_LEN_MAX;
+
+ return m->nb_segs + RTE_MIN(m->nb_segs * extra_descs_per_seg,
+ extra_descs_per_pkt);
+}
+