linux-kernel - Re: Can Linux live without DMA zone?

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Date:	Thu, 02 Nov 2006 14:08:39 -0500
From:	Phillip Susi <psusi@....rr.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Jun Sun <jsun@...sun.net>, linux-kernel@...r.kernel.org
Subject: Re: Can Linux live without DMA zone?

Arjan van de Ven wrote:
> that is a nice theory, but unfortunately there is just a lot of "PCI"
> hardware out there for which the designers decided to save a bit of
> copper and only wire up the lower X address lines (for various values of
> X)

Yea, but shouldn't PCI drivers be using another means than allocating 
from GFP_DMA?  Wasn't there some sort of bounce buffers call I can't 
quite remember the details of?  That performs any required translations 
to bus hardware addresses, and copies the buffer to a more appropriate 
location if required, based on the specific requirements of that device?

I know that most 32 bit PCI devices can't handle addresses above the 4 
GB mark on 64 bit machines, but those drivers should NOT be limiting DMA 
to the first 16 MB.  Especially since most machines don't have over 4 GB 
of ram anyhow, but quite often original buffers will be above 16 MB.

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