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SubjectRe: [BISECTED REGRESSION] b43legacy broken on G4 PowerBook
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On 6/11/19 5:46 PM, Benjamin Herrenschmidt wrote:
> On Tue, 2019-06-11 at 17:20 -0500, Larry Finger wrote:
>> b43-pci-bridge 0001:11:00.0: dma_direct_supported: failed (mask =
>> 0x3fffffff,
>> min_mask = 0x5ffff000/0x5ffff000, dma bits = 0x1f
>
> Ugh ? A mask with holes in it ? That's very wrong... That min_mask is
> bogus.

I agree, but that is not likely serious as most systems will have enough memory
that the max_pfn term will be much larger than the initial min_mask, and
min_mask will be unchanged by the min function. In addition, min_mask is not
used beyond this routine, and then only to decide if direct dma is supported.
The following patch generates masks with no holes, but I cannot see that it is
needed.

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 2c2772e9702a..e3edd4f29e80 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -384,7 +384,8 @@ int dma_direct_supported(struct device *dev, u64 mask)
else
min_mask = DMA_BIT_MASK(32);

- min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
+ min_mask = min_t(u64, min_mask, ((max_pfn - 1) << PAGE_SHIFT) |
+ DMA_BIT_MASK(PAGE_SHIFT));

/*
* This check needs to be against the actual bit mask value, so

Larry

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