dma-direct: comment the dma_direct_free calling convention

Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/lib/dma-direct.c b/lib/dma-direct.c
index fdc733cf9e30a9239bf5bd497e383502081c4418..c9e8e21cb33406f33b539cfd25d82b5749071422 100644 (file)
--- a/lib/dma-direct.c
+++ b/lib/dma-direct.c
@@ -84,6 +84,10 @@ again:
        return page_address(page);
 }
 
+/*
+ * NOTE: this function must never look at the dma_addr argument, because we want
+ * to be able to use it as a helper for iommu implementations as well.
+ */
 void dma_direct_free(struct device *dev, size_t size, void *cpu_addr,
                dma_addr_t dma_addr, unsigned long attrs)
 {