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

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 47aeb04c1997..de7cc540450f 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -719,7 +719,7 @@ swiotlb_alloc_buffer(struct device *dev, size_t size, 
dma_addr_t *dma_handle,
                goto out_warn;
        *dma_handle = __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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