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Subject[PATCH 4.16 058/196] swiotlb: fix unexpected swiotlb_alloc_coherent failures
4.16-stable review patch.  If anyone has any objections, please let me know.


From: Takashi Iwai <>

commit 9e7f06c8beee304ee21b791653fefcd713f48b9a upstream.

The code refactoring by commit 0176adb00406 ("swiotlb: refactor coherent
buffer allocation") made swiotlb_alloc_buffer almost always failing due
to a thinko: namely, the function evaluates the dma_coherent_ok call
incorrectly and dealing as if it's invalid. This ends up with weird
errors like iwlwifi probe failure or amdgpu screen flickering.

This patch corrects the logic error.

Fixes: 0176adb00406 ("swiotlb: refactor coherent buffer allocation")
Cc: <> # v4.16+
Signed-off-by: Takashi Iwai <>
Signed-off-by: Christoph Hellwig <>
Cc: Jean Delvare <>
Signed-off-by: Greg Kroah-Hartman <>

lib/swiotlb.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -732,7 +732,7 @@ swiotlb_alloc_buffer(struct device *dev,
goto out_warn;

*dma_handle = swiotlb_phys_to_dma(dev, phys_addr);
- if (dma_coherent_ok(dev, *dma_handle, size))
+ if (!dma_coherent_ok(dev, *dma_handle, size))
goto out_unmap;

memset(phys_to_virt(phys_addr), 0, size);

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