linux-kernel - Re: [PATCH 06/10] swiotlb: use swiotlb_map_page in swiotlb_map_sg

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Date:   Wed, 14 Nov 2018 17:12:39 +0100
From:   Christoph Hellwig <hch@....de>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Christoph Hellwig <hch@....de>, Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH 06/10] swiotlb: use swiotlb_map_page in
 swiotlb_map_sg_attrs

On Wed, Nov 14, 2018 at 03:13:11PM +0100, Christoph Hellwig wrote:
> Does the patch below make a difference for you?  Assigning an
> address to the S/G list is the only functional difference I could
> spot.  Drivers really should never look at the S/G list on an
> error return, but..

And that was obviously just the second half of the patch, so here
is the full one:

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 5731daa09a32..a896f46d0c31 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -786,10 +786,13 @@ swiotlb_map_sg_attrs(struct device *dev, struct scatterlist *sgl, int nelems,
 	int i;
 
 	for_each_sg(sgl, sg, nelems, i) {
-		sg->dma_address = swiotlb_map_page(dev, sg_page(sg), sg->offset,
+		dma_addr_t dma_addr;
+
+		dma_addr = swiotlb_map_page(dev, sg_page(sg), sg->offset,
 				sg->length, dir, attrs);
-		if (sg->dma_address == DIRECT_MAPPING_ERROR)
+		if (dma_addr == DIRECT_MAPPING_ERROR)
 			goto out_error;
+		sg->dma_address = dma_addr;
 		sg_dma_len(sg) = sg->length;
 	}