quoted

+    if (mask > dev->archdata.parent_dma_mask)
+        mask = dev->archdata.parent_dma_mask;
+
+

   One empty line is enough...

Ok

quoted

+    /*
+     * Whatever the parent bus can set. A device must not set
+     * a DMA mask larger than this.
+     */
+    dev->archdata.parent_dma_mask = size;

   Not 'size - 1'?

Good question.

Indeed of_dma_configure() calls arch_setup_dma_ops() with size, not
mask. Which implies '-1' is needed here. Although better fix may be to
change caller side - to make DMA_BIT_MASK(64) case cleaner.

Will repost path.

Nikita