Re: How to create a kernel virtual mapping for physical addresses.

[Arnd Bergmann]

On Saturday 09 April 2011 00:03:21 brace@xxxxxxxxxxxxxxxxxx wrote:
> Given a physical address and a length (which may span contiguous pages), how
> does one go about creating a virtual mapping for that address? That address may
> be in high memory (above 4GB) in a 32bit system.
> 
> ioremap() wants a 32bit physical address on 32bit systems. kmap() and
> kmap_atomic() wants a struct page which I am not sure how to get from a physical
> address.

Use kmap() on the page you get from pfn_to_page().

> If there already is a kernel mapping, then using the existing kernel mapping
> would be fine if I could figure out how to get it, but if there is not one,
> then I need to make one.
> 
> I think setting the DMA mask to 32bit would mean that I do not have to deal
> with highmem addresses in my particular case, but I still do not know how to
> get a virtual address from a physical.
 
DMA mask is only about devices doing DMA to your data, not about the
kernel touching it.

	Arnd
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