Date: Thu, 11 Oct 2007 22:18:15 -0600
From: Robert Hancock <hancockr@shaw.ca>
Subject: Re: ioremap_nocache and mem= parameter with k 2.6.18
In-reply-to: <1192116465.689041.176900@57g2000hsv.googlegroups.com>
To: mirco_cremasco@hotmail.com, linux-kernel <linux-kernel@vger.kernel.org>
Message-id: <470EF587.3000204@shaw.ca>
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mirco_cremasco@hotmail.com wrote:
> Hi,
> I'm using a driver for a framegrabber device that needs to alloc a
> huge buffer of ram for dma transfers....
> So it works:
> 1) Having 2GB of ram installed, boot the kernel with mem=1024M
> parameter
> 2) remap the unmapped memory above first GB using ioremap_nocache
> function, using PAGE_ALIGN().
> 
> This works fine with kernel 2.6.9 but it doesn't with newer ones
> 2.6.18, 2.6.20, 2.6.22.
> With newer kernel ioremap returns 0.
> It seems like memory above 1G has been marked reserved, IMHO.
> 
> What changes in the mm?
> I'm not the driver's developer, but I'd like to understand and
> possibly find a workaround...

It doesn't make sense to use ioremap_nocache on RAM. It's only meant for 
mapping MMIO memory regions on a device.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

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