linux-kernel - Re: Disabling DMA with ICH10?

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Message-ID: <20090928223727.0b1367b7@varda>
Date:	Mon, 28 Sep 2009 22:37:27 +0200
From:	Alejandro Riveira Fernández 
	<ariveira@...il.com>
To:	FunFlyer@....net
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Disabling DMA with ICH10?

El Mon, 28 Sep 2009 23:31:21 +0200
Lennart Baruschka <FunFlyer@....net> escribió:

> Hello,
> 
> I'm new to this list, so please forgive me if this is the wrong place to
> ask. I'm trying to build a 2.6.30.5 kernel causing as little DMA traffic
> as possible in order to reduce latencies on a real-time system (using
> RTAI). 
> 
> 1. Is there a way to completely disable DMA usage system-wide?
> If not:
> 2. My system uses an ICH10 chipset, the harddrive is connected to the
> Intel SATA controller. Is there a way to disable DMA and switch back to
> PIO? I tried compiling with libata support and without SCSI support, but
> the kernel is unable to mount root (no matter if /dev/sda1
> or /dev/hda1), then.
  
  AFAIK libata needs scsi support. To disable dma in libata I get from
  Documentation/kernel-parameters.txt --> libata.dma = 0


> 3. Another source seems to be the ATL1E driver for ethernet. Is it
> possible to either disable DMA for this? 
  
  That I dunno

> 
> If disabling DMA is impossible for some reason for one or both drivers,
> is it at least possible to reduce the burst sizes so the bus gets free
> for a short time during which I could access it from my real time kernel
> module?
> 
> Please point me in the right direction; any suggestion will be greatly
> appreciated!
> 
> Cheers,
> Lennart
   
  Saludos,
  Alejandro 


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