linux-kernel - Re: ioremap_nocache and mem= parameter with k 2.6.18

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Date:	Thu, 11 Oct 2007 22:18:15 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	mirco_cremasco@...mail.com,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: ioremap_nocache and mem= parameter with k 2.6.18

mirco_cremasco@...mail.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@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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