+static inline void niu_sync_rx_discard_stats(struct niu *np,
+ struct rx_ring_info *rp,
+ const int limit)
+{
+ /* This elaborate scheme is needed for reading the RX discard
+ * counters, as they are only 16-bit and can overflow quickly,
+ * and because the overflow indication bit is not usable as
+ * the counter value does not wrap, but remains at max value
+ * 0xFFFF.
+ *
+ * In theory and in practice counters can be lost in between
+ * reading nr64() and clearing the counter nw64(). For this
+ * reason, the number of counter clearings nw64() is
+ * limited/reduced though the limit parameter.
+ */
+ int rx_channel = rp->rx_channel;
+ u32 misc, wred;
+
+ /* RXMISC (Receive Miscellaneous Discard Count), covers the
+ * following discard events: IPP (Input Port Process),
+ * FFLP/TCAM, Full RCR (Receive Completion Ring) RBR (Receive
+ * Block Ring) prefetch buffer is empty.
+ */
+ misc = nr64(RXMISC(rx_channel));
+ if (unlikely((misc & RXMISC_COUNT) > limit)) {
+ nw64(RXMISC(rx_channel), 0);
+ rp->rx_errors += misc & RXMISC_COUNT;
+
+ if (unlikely(misc & RXMISC_OFLOW))
+ dev_err(np->device, "rx-%d: Counter overflow "
+ "RXMISC discard\n", rx_channel);
+
+ niudbg(RX_ERR, "%s-rx-%d: MISC drop=%u over=%u\n",
+ np->dev->name, rx_channel, misc, misc-limit);
+ }
+
+ /* WRED (Weighted Random Early Discard) by hardware */
+ wred = nr64(RED_DIS_CNT(rx_channel));
+ if (unlikely((wred & RED_DIS_CNT_COUNT) > limit)) {
+ nw64(RED_DIS_CNT(rx_channel), 0);
+ rp->rx_dropped += wred & RED_DIS_CNT_COUNT;
+
+ if (unlikely(wred & RED_DIS_CNT_OFLOW))
+ dev_err(np->device, "rx-%d: Counter overflow "
+ "WRED discard\n", rx_channel);
+
+ niudbg(RX_ERR, "%s-rx-%d: WRED drop=%u over=%u\n",
+ np->dev->name, rx_channel, wred, wred-limit);
+ }
+}
+