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Date: Wed, 16 Mar 2011 17:43:55 +0100
From: Alexander Graf <agraf@suse.de>
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Subject: [Qemu-devel] Re: [PATCH 25/26] Add a PAPR TCE-bypass mechanism for
 the pSeries machine
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To: David Gibson <david@gibson.dropbear.id.au>
Cc: paulus@samba.org, qemu-devel@nongnu.org, anton@samba.org

On 03/16/2011 05:57 AM, David Gibson wrote:
> From: Ben Herrenschmidt<benh@kernel.crashing.org>
>
> Usually, PAPR virtual IO devices use a virtual IOMMU mechanism, TCEs,
> to mediate all DMA transfers.  While this is necessary for some sorts of
> operation, it can be complex to program and slow for others.
>
> This patch implements a mechanism for bypassing TCE translation, treating
> "IO" addresses as plain (guest) physical memory addresses.  This has two
> main uses:
>   * Simple, but 64-bit aware programs like firmwares can use the VIO devices
> without the complexity of TCE setup.
>   * The guest OS can optionally use the TCE bypass to improve performance in
> suitable situations.
>
> The mechanism used is a per-device flag which disables TCE translation.
> The flag is toggled with some (hypervisor-implemented) RTAS methods.

Is this an official extension used by anyone or is it your own invention 
that's not implemented in pHyp?


Alex