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Subject[PATCH 2/2] swiotlb: Fix dma_supported() to consider direct allocation
Along with the recent change to use the common swiotlb dma_ops, x86
also takes over the swiotlb_dma_supported(). This caused a regression
when a low bit DMA mask is set; e.g. parport_pc driver now fails to
set the 24bit DMA mask:

parport_pc parport_pc.956: Unable to set coherent dma mask: disabling DMA

It's because swiotlb_dma_supported() only checks the swiotlb range,
and the 24bit DMA mask is below io_tlb_end. OTOH, in the past kernel
versions, x86's swiotlb dma_supported() was NULL, which was
effectively evaluated as the direct DMA, hence the lower DMA mask was

This patch fixes the regression by extending swiotlb_dma_supported()
to check the direct DMA at first for covering the primary allocation
before swiotlb.

Fixes: 6e4bf5867783 ("x86/dma: Use generic swiotlb_ops")
Signed-off-by: Takashi Iwai <>
lib/swiotlb.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index de7cc540450f..a81502ea79e7 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -1042,6 +1042,10 @@ swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
swiotlb_dma_supported(struct device *hwdev, u64 mask)
+ if (dma_direct_supported(hwdev, mask))
+ return 1;
return __phys_to_dma(hwdev, io_tlb_end - 1) <= mask;

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