From: Krishna Reddy <[email protected]>
Subject: RE: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper
Date: Tue, 6 Mar 2012 23:48:42 +0100
Message-ID: <[email protected]>
> > > +struct dma_iommu_mapping *
> > > +arm_iommu_create_mapping(struct bus_type *bus, dma_addr_t base, size_t
> > > size,
> > > + int order)
> > > +{
> > > + unsigned int count = (size >> PAGE_SHIFT) - order;
> > > + unsigned int bitmap_size = BITS_TO_LONGS(count) * sizeof(long);
>
> The count calculation doesn't seem correct. "order" is log2 number and
> size >> PAGE_SHIFT is number of pages.
>
> If size is passed as 64*4096(256KB) and order is 6(allocation granularity is
> 2^6 pages=256KB),
> just 1 bit is enough to manage allocations. So it should be 4 bytes or one
> long.
Good catch!
> But the calculation gives count = 64 - 6 = 58 and
> Bitmap_size gets set to (58/(4*8)) * 4 = 8 bytes, which is incorrect.
"order" isn't the order of size passed, which is minimal *page*
allocation order which client decides whatever, just in case.
> It should be as follows.
> unsigned int count = 1 << get_order(size) - order;
> unsigned int bitmap_size = BITS_TO_LONGS(count) * sizeof(long) *
> BITS_PER_BYTE;
>
> -KR
>
> --nvpublic
>
>
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