Re: [PATCH 06/10] swiotlb: use swiotlb_map_page in swiotlb_map_sg_attrs

[Christoph Hellwig]

On Mon, Nov 19, 2018 at 03:22:13PM -0800, John Stultz wrote:
> > +               sg->dma_address = dma_addr;
> >                 sg_dma_len(sg) = sg->length;
> >         }
> 
> I know Robin has already replied with more detailed info, but just to
> close the loop as I'm finally home, applying this patch didn't seem to
> help with the IO hangs I'm seeing w/ HiKey960.

If Robins observation is right this should fix the problem for you:

diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index bd73e7a91410..1833f0c1fba0 100644
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -5,7 +5,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/mem_encrypt.h>
 
-#define DIRECT_MAPPING_ERROR		0
+#define DIRECT_MAPPING_ERROR		(~(dma_addr_t)0x0)
 
 #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
 #include <asm/dma-direct.h>