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From: "Christophe Beaumont" <christophe@paracel.com>
To: <root@chaos.analogic.com>
Cc: "kernel Linux" <linux-kernel@vger.kernel.org>
Subject: RE: DMA memory limitation?
Date: Thu, 5 Jul 2001 10:07:17 -0700
Message-ID: <NFBBINOGHMOOBMPNBAHKCEPECEAA.christophe@paracel.com>
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> On Thu, 5 Jul 2001, Vasu Varma P V wrote:
> 
> > Hi,
> > 
> > Is there any limitation on DMA memory we can allocate using
> > kmalloc(size, GFP_DMA)? I am not able to acquire more than
> > 14MB of the mem using this on my PCI SMP box with 256MB ram.
> > I think there is restriction on ISA boards of 16MB.
> > Can we increase it ?
> > 
> > thx,
> > Vasu
> 
> 14MB of DMA(able) memory?  Err. I think you are trying to
> do something you would never need to do.
> 
And what is that supposed to be????

I have a piece of pretty well designed hardware here... and my
application requires me to have the PCI board to random access
in master mode a whole lot of memory (anywhere from 128MEGS to
1GIG... and possibly more...) so I really do need BIG DMA buffers
(I don't say huge anymore as one can get 1/2 Gig of RAM for just
over 120 bucks???)... 

There is no way I can have the piece of hardware behave in 
another fashion... and NO it is NOT broken (when you do BOTH 
hardware & software, you know about BOTH limitations... there
are just some cases where you have to face some unique issues).
the mem=1024M works pretty fine once you have figured out how 
to handle in a fairly simple way this "reserved" memory...

So please software people... do not blame it all on the 
hardware... =)

Chris.
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