From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:36978)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <agraf@suse.de>) id 1b8qz5-0006uo-PY
	for qemu-devel@nongnu.org; Fri, 03 Jun 2016 11:26:04 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <agraf@suse.de>) id 1b8qz4-0000b2-NM
	for qemu-devel@nongnu.org; Fri, 03 Jun 2016 11:26:03 -0400
References: <1464870382-385-1-git-send-email-bogdan.purcareata@nxp.com>
	<1464870382-385-3-git-send-email-bogdan.purcareata@nxp.com>
	<CAFEAcA9yTmT+5zDYJjmLDvxmdOiEfAxKxjCYuYKfOwUrft1Drg@mail.gmail.com>
	<AM2PR04MB0739ED319596E29E8018D8EA84590@AM2PR04MB0739.eurprd04.prod.outlook.com>
	<CAFEAcA9Q5NOy5u5Y8Sa4nE43WkzgQFi0BrdMwtyUcQ-WXO_EAA@mail.gmail.com>
	<AM2PR04MB07394390024600CB1DD9918084590@AM2PR04MB0739.eurprd04.prod.outlook.com>
From: Alexander Graf <agraf@suse.de>
Message-ID: <5751A180.8040407@suse.de>
Date: Fri, 3 Jun 2016 17:25:52 +0200
MIME-Version: 1.0
In-Reply-To: <AM2PR04MB07394390024600CB1DD9918084590@AM2PR04MB0739.eurprd04.prod.outlook.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 2/2] arm/virt: Mark pcie controller node as
 dma-coherent
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Mihai Claudiu Caraman <mike.caraman@nxp.com>, Peter Maydell <peter.maydell@linaro.org>
Cc: Bogdan Purcareata <bogdan.purcareata@nxp.com>, QEMU Developers <qemu-devel@nongnu.org>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, qemu-arm <qemu-arm@nongnu.org>, Eric Auger <eric.auger@linaro.org>

On 06/03/2016 05:16 PM, Mihai Claudiu Caraman wrote:
>> -----Original Message-----
>> From: Peter Maydell [mailto:peter.maydell@linaro.org]
>> Sent: Friday, June 03, 2016 5:38 PM
>> To: Mihai Claudiu Caraman <mike.caraman@nxp.com>
>> Cc: Bogdan Purcareata <bogdan.purcareata@nxp.com>; QEMU Developers <qemu-devel@nongnu.org>; Peter Crosthwaite <crosthwaite.peter@gmail.com>; Alexander Graf <agraf@suse.de>; qemu-arm <qemu-arm@nongnu.org>; Eric Auger <eric.auger@linaro.org>
>> Subject: Re: [Qemu-devel] [PATCH 2/2] arm/virt: Mark pcie controller node as dma-coherent
>>
>> On 3 June 2016 at 15:22, Mihai Claudiu Caraman <mike.caraman@nxp.com> wrote:
>>> In particular for virtual and emulated devices the host CPU behaves as
>>> a DMA coherent 'device'. This should have been stated in patch
>>> description.
>> Wouldn't that imply that we should just always have the "dma-coherent"
>> property set, and we don't need to do any of the messing around looking at the host sysfs ?
>>
>> thanks
>> -- PMM
> We can always set "dma-coherent" for virtual and emulated devices but not for passthrough devices. So we can't have one PCIe controller for all devices marked as "dma-coherent".

The original patch is about the case where PCI is already cache coherent 
on the host.

I think at the end of the day this is simply outside of QEMU's scope to 
decide. What we can do is set dma-coherent per default (if Will and Ard 
agree) on the default PCIe bus and add code that allows to spawn a 
secondary PCIe bus which can then have different dma-coherent attributes 
and that you can then plug your non-coherent vfio devices into.


Alex