+/*
+ * TX and RX descriptors are 16 bytes. This causes problems with the cache
+ * maintenance on CPUs where the cache-line size exceeds the size of these
+ * descriptors. What will happen is that when the driver receives a packet
+ * it will be immediately requeued for the hardware to reuse. The CPU will
+ * therefore need to flush the cache-line containing the descriptor, which
+ * will cause all other descriptors in the same cache-line to be flushed
+ * along with it. If one of those descriptors had been written to by the
+ * device those changes (and the associated packet) will be lost.
+ *
+ * To work around this, we make use of non-cached memory if available. If
+ * descriptors are mapped uncached there's no need to manually flush them
+ * or invalidate them.
+ *
+ * Note that this only applies to descriptors. The packet data buffers do
+ * not have the same constraints since they are 1536 bytes large, so they
+ * are unlikely to share cache-lines.
+ */
+static void *rtl_alloc_descs(unsigned int num)
+{
+ size_t size = num * RTL8169_DESC_SIZE;
+
+#ifdef CONFIG_SYS_NONCACHED_MEMORY
+ return (void *)noncached_alloc(size, RTL8169_ALIGN);
+#else
+ return memalign(RTL8169_ALIGN, size);
+#endif
+}
+