[PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper

[Hiroshi Doyu]

From: Krishna Reddy <vdumpa at nvidia.com>
Subject: RE: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper
Date: Tue, 6 Mar 2012 23:48:42 +0100
Message-ID: <401E54CE964CD94BAE1EB4A729C7087E37970113FE at HQMAIL04.nvidia.com>

> > > +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
> 
>