linux-kernel - Re: A question about ZONE

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Message-Id: <201010131657.07187.oneukum@suse.de>
Date:	Wed, 13 Oct 2010 16:57:07 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Casey Dahlin <cdahlin@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: A question about ZONE_DMA

Am Mittwoch, 13. Oktober 2010, 16:52:41 schrieb Casey Dahlin:
> Hi all,
> 
> So if I understand correctly, ZONE_DMA exists to separate and preserve the
> chunk of memory to which older ISA cards are capable of doing DMA. The question
> that arises for me is:
> 
> 1) Why do /all/ 32-bit boxes have a ZONE_DMA when surely only a tiny and
> shrinking number of them have a need for it?

You don't know before you load the module of the driver that needs it.

> 2) Why do /any/ 64-bit boxes have a ZONE_DMA? Is there really some godless
> monster out there who put an early ISA bridge and a 64-bit CPU on the same
> motherboard?!

Parports can use DMA and are generally ISA.

	Regards
		Oliver
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