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Date:	Sun, 4 Apr 2010 02:16:19 -0600
From:	Thomas Fjellstrom <tfjellstrom@...angesoft.net>
To:	linux-kernel@...r.kernel.org
Subject: Re: Fwd: Can we remove the Zone_DMA?

On April 4, 2010, Daniel Hazelton wrote:
> On Sunday 04 April 2010 01:33:09 am tek-life wrote:
> > Thanks for your reply.And do you means that , If I use a modern PC,such
> > as my pc (CPU:Intel dual-core 2.6GHZ; Memory 2GB; And no pci ).I can
> > remove the ZONE_DMA .And make sure this system also run smoothly as
> > before?
> 
> *MAYBE* - if you don't use parallel ports, floppy drives or similar.
> There actually are still a lot of devices that use the ISA bus in a
> modern PC - even the keyboard (well, not USB ones) is an ISA device.
> 
> Simple fact is that if it was possible to configure it out and not cause
> massive problems somebody would have already spun out a patch to allow
> just that.

Some onboard motherboard devices may also be ISA devices.

> DRH
> 
> > 在 2010年4月4日 下午1:07,Daniel Hazelton <dhazelton@...er.net>写道:
> > 
> > On Sunday 04 April 2010 12:21:54 am tek-life wrote:
> > > > I’m a newbie on the linux kernel. Now I am reading the source code
> > > > of Linux . I have a question in the following about ZONE_DMA.
> > > > 
> > > > 
> > > > In Linux , The Memory is divided to three zone. They are ZONE_DMA
> > > > 、ZONE_NORMAL  and ZONE_HIGHMEM. From the book of "Undstand the
> > > > Linux kernel ", the ZONE_DMA has the effect that the Direct Memory
> > > > Access (DMA) processors for old ISA buses have a strong
> > > > limitation: they are able to address only the first 16 MB of RAM.
> > > > SO ,we must set a zone for  the DMA on ISA bus.  And I suspect
> > > > that the hardware has developed so quickly .And  in this days the
> > > > ISA has been weeded out. And so ,if we not defined the ZONE_DMA,
> > > > is the system be effected? And why not remove ZONE_DMA from the
> > > > kernel . If it cann‘t to do so,the compatibility is the only
> > > > reason?
> > > 
> > > While ISA is gone as a true peripheral interconnect for new systems
> > > it does,
> > > actually, still live on in a lot of systems that Linux still
> > > supports. While
> > > those systems, generally, are running the same kernel and userspace
> > > they were
> > > a decade ago I have no doubt that somebody might find an old machine
> > > and put
> > > Linux on it - just because they could.
> > > 
> > > And that also discounts the non-IBM PC machines that are out there
> > > that Linux
> > > also supports. While I don't know enough about them to say for sure,
> > > I am quite certain that at least some of them are still using the
> > > ISA bus.
> > > 
> > > DRH
> 
> --
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-- 
Thomas Fjellstrom
tfjellstrom@...angesoft.net
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