* Re: ioremap_nocache and mem= parameter with k 2.6.18
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@ 2007-10-12 4:18 ` Robert Hancock
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From: Robert Hancock @ 2007-10-12 4:18 UTC (permalink / raw)
To: mirco_cremasco, linux-kernel
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
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