+/**
+ * pdc_desc_count() - Count the number of DMA descriptors that will be required
+ * for a given scatterlist. Account for the max length of a DMA buffer.
+ * @sg: Scatterlist to be DMA'd
+ * Return: Number of descriptors required
+ */
+static u32 pdc_desc_count(struct scatterlist *sg)
+{
+ u32 cnt = 0;
+
+ while (sg) {
+ cnt += ((sg->length / PDC_DMA_BUF_MAX) + 1);
+ sg = sg_next(sg);
+ }
+ return cnt;
+}
+
+/**
+ * pdc_rings_full() - Check whether the tx ring has room for tx_cnt descriptors
+ * and the rx ring has room for rx_cnt descriptors.
+ * @pdcs: PDC state
+ * @tx_cnt: The number of descriptors required in the tx ring
+ * @rx_cnt: The number of descriptors required i the rx ring
+ *
+ * Return: true if one of the rings does not have enough space
+ * false if sufficient space is available in both rings
+ */
+static bool pdc_rings_full(struct pdc_state *pdcs, int tx_cnt, int rx_cnt)
+{
+ u32 rx_avail;
+ u32 tx_avail;
+ bool full = false;
+
+ /* Check if the tx and rx rings are likely to have enough space */
+ rx_avail = pdcs->nrxpost - NRXDACTIVE(pdcs->rxin, pdcs->rxout,
+ pdcs->nrxpost);
+ if (unlikely(rx_cnt > rx_avail)) {
+ pdcs->rx_ring_full++;
+ full = true;
+ }
+
+ if (likely(!full)) {
+ tx_avail = pdcs->ntxpost - NTXDACTIVE(pdcs->txin, pdcs->txout,
+ pdcs->ntxpost);
+ if (unlikely(tx_cnt > tx_avail)) {
+ pdcs->tx_ring_full++;
+ full = true;
+ }
+ }
+ return full;
+}
+
+/**
+ * pdc_last_tx_done() - If both the tx and rx rings have at least
+ * PDC_RING_SPACE_MIN descriptors available, then indicate that the mailbox
+ * framework can submit another message.
+ * @chan: mailbox channel to check
+ * Return: true if PDC can accept another message on this channel
+ */
+static bool pdc_last_tx_done(struct mbox_chan *chan)
+{
+ struct pdc_state *pdcs = chan->con_priv;
+ bool ret;
+
+ if (unlikely(pdc_rings_full(pdcs, PDC_RING_SPACE_MIN,
+ PDC_RING_SPACE_MIN))) {
+ pdcs->last_tx_not_done++;
+ ret = false;
+ } else {
+ ret = true;
+ }
+ return ret;
+}
+