linux-kernel - [PATCH 2/2] swiotlb: Fix dma_supported() to consider direct allocation

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Date:   Sun, 15 Apr 2018 11:08:08 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Christoph Hellwig <hch@....de>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
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
allowed.

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 <tiwai@...e.de>
---
 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)
 int
 swiotlb_dma_supported(struct device *hwdev, u64 mask)
 {
+#ifdef CONFIG_DMA_DIRECT_OPS
+	if (dma_direct_supported(hwdev, mask))
+		return 1;
+#endif
 	return __phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
 }

-- 
2.16.3