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* [PATCH RESEND v2] ARM: dma-api: fix max_pfn off-by-one error in __dma_supported()
@ 2019-12-24  3:02 ` Chen-Yu Tsai
  0 siblings, 0 replies; 4+ messages in thread
From: Chen-Yu Tsai @ 2019-12-24  3:02 UTC (permalink / raw)
  To: Russell King, Christoph Hellwig, Andrew Morton
  Cc: Chen-Yu Tsai, Robin Murphy, linux-arm-kernel, linux-kernel, stable

From: Chen-Yu Tsai <>

max_pfn, as set in arch/arm/mm/init.c:

    static void __init find_limits(unsigned long *min,
				   unsigned long *max_low,
				   unsigned long *max_high)
	    *max_low = PFN_DOWN(memblock_get_current_limit());
	    *min = PFN_UP(memblock_start_of_DRAM());
	    *max_high = PFN_DOWN(memblock_end_of_DRAM());

with memblock_end_of_DRAM() pointing to the next byte after DRAM. As
such, max_pfn points to the PFN after the end of DRAM.

Thus when using max_pfn to check DMA masks, we should subtract one
when checking DMA ranges against it.

Commit 8bf1268f48ad ("ARM: dma-api: fix off-by-one error in
__dma_supported()") fixed the same issue, but missed this spot.

This issue was found while working on the sun4i-csi v4l2 driver on the
Allwinner R40 SoC. On Allwinner SoCs, DRAM is offset at 0x40000000,
and we are starting to use of_dma_configure() with the "dma-ranges"
property in the device tree to have the DMA API handle the offset.

In this particular instance, dma-ranges was set to the same range as
the actual available (2 GiB) DRAM. The following error appeared when
the driver attempted to allocate a buffer:

    sun4i-csi 1c09000.csi: Coherent DMA mask 0x7fffffff (pfn 0x40000-0xc0000)
    covers a smaller range of system memory than the DMA zone pfn 0x0-0xc0001
    sun4i-csi 1c09000.csi: dma_alloc_coherent of size 307200 failed

Fixing the off-by-one error makes things work.

Fixes: 11a5aa32562e ("ARM: dma-mapping: check DMA mask against available memory")
Fixes: 9f28cde0bc64 ("ARM: another fix for the DMA mapping checks")
Fixes: ab746573c405 ("ARM: dma-mapping: allow larger DMA mask than supported")
Cc: <>
Signed-off-by: Chen-Yu Tsai <>

It's been close to two weeks since I sent this. I wasn't sure if I
reached the right maintainers, so I'm resending this to more people.

Changes since v1:

  - correct max_pfn offset in the correct place.

 arch/arm/mm/dma-mapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index e822af0d9219..9414d72f664b 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -221,7 +221,7 @@ EXPORT_SYMBOL(arm_coherent_dma_ops);
 static int __dma_supported(struct device *dev, u64 mask, bool warn)
-	unsigned long max_dma_pfn = min(max_pfn, arm_dma_pfn_limit);
+	unsigned long max_dma_pfn = min(max_pfn - 1, arm_dma_pfn_limit);
 	 * Translate the device's DMA mask to a PFN limit.  This

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2020-01-09 14:39 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-12-24  3:02 [PATCH RESEND v2] ARM: dma-api: fix max_pfn off-by-one error in __dma_supported() Chen-Yu Tsai
2019-12-24  3:02 ` Chen-Yu Tsai
2020-01-09 14:38 ` Christoph Hellwig
2020-01-09 14:38   ` Christoph Hellwig

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