MIPS: DMA: Explain the lack of special handling for R14000/R16000.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/dma-default.c

@@ -61,6 +61,11 @@ static inline struct page *dma_addr_to_page(struct device *dev,
  * Warning on the terminology - Linux calls an uncached area coherent;
  * MIPS terminology calls memory areas with hardware maintained coherency
  * coherent.
+ *
+ * Note that the R14000 and R16000 should also be checked for in this
+ * condition.  However this function is only called on non-I/O-coherent
+ * systems and only the R10000 and R12000 are used in such systems, the
+ * SGI IP28 Indigo² rsp. SGI IP32 aka O2.
  */
 static inline int cpu_needs_post_dma_flush(struct device *dev)
 {