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Message-Id: <201104192151.41511.arnd@arndb.de> Date: Tue, 19 Apr 2011 21:51:41 +0200 From: Arnd Bergmann <arnd@...db.de> To: brace@...rdog.cce.hp.com Cc: linux-kernel@...r.kernel.org, scameron@...rdog.cce.hp.com Subject: Re: How to create a kernel virtual mapping for physical addresses. On Saturday 09 April 2011 00:03:21 brace@...rdog.cce.hp.com 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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