From: Krishna Reddy <vdumpa@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> > > > +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 > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href