From: Arnd Bergmann <arnd@arndb.de>
To: brace@beardog.cce.hp.com
Cc: linux-kernel@vger.kernel.org, scameron@beardog.cce.hp.com
Subject: Re: How to create a kernel virtual mapping for physical addresses.
Date: Tue, 19 Apr 2011 21:51:41 +0200 [thread overview]
Message-ID: <201104192151.41511.arnd@arndb.de> (raw)
In-Reply-To: <20110408220321.GA777@beardog.cce.hp.com>
On Saturday 09 April 2011 00:03:21 brace@beardog.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
next prev parent reply other threads:[~2011-04-19 19:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-08 22:03 How to create a kernel virtual mapping for physical addresses brace
2011-04-19 19:51 ` Arnd Bergmann [this message]
[not found] ` <20110421184600.GA29746@beardog.cce.hp.com>
2011-04-21 19:36 ` Arnd Bergmann
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