Re: Is iommu_num_pages() broken ?

[Andreas Schwab <schwab@linux-m68k.org>]

Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:

> static inline unsigned long iommu_num_pages(unsigned long addr,
> 					    unsigned long len,
> 					    unsigned long io_page_size)
> {
> 	unsigned long size = (addr & (io_page_size - 1)) + len;
>
> 	return DIV_ROUND_UP(size, io_page_size);
> }
>  
>
> That doesn't look right to me...
>
> The powerpc iommu code at least uses that with an addr which may not be
> page aligned (ie, result of sg_virt() which include the offset).
>
> The above code will align the start before adding the len which is wrong

addr & (io_page_size - 1) computes the offset into the page pointed to
by addr.  Looks right to me.

addr & ~(io_page_size - 1) would round addr down to the start of the
page.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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