linux-kernel - [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap

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Date:   Wed, 29 May 2019 01:15:32 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Joerg Roedel <joro@...tes.org>, Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] iommu/dma: Fix condition check in iommu_dma_unmap_sg

Clang warns:

drivers/iommu/dma-iommu.c:897:6: warning: logical not is only applied to
the left hand side of this comparison [-Wlogical-not-parentheses]
        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
            ^                                 ~~
drivers/iommu/dma-iommu.c:897:6: note: add parentheses after the '!' to
evaluate the comparison first
        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
            ^
             (                                    )
drivers/iommu/dma-iommu.c:897:6: note: add parentheses around left hand
side expression to silence this warning
        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
            ^
            (                                )
1 warning generated.

Judging from the rest of the commit and the conditional in
iommu_dma_map_sg, either

    if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))

or
    if ((attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)

was intended, not a combination of the two.

I personally think that the former is easier to understand so use that.

Fixes: 06d60728ff5c ("iommu/dma: move the arm64 wrappers to common code")
Link: https://github.com/ClangBuiltLinux/linux/issues/497
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 drivers/iommu/dma-iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 0cd49c2d3770..0dee374fc64a 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -894,7 +894,7 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
 	struct scatterlist *tmp;
 	int i;
 
-	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
+	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
 		iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
 
 	/*
-- 
2.22.0.rc1