From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:42914)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <borntraeger@de.ibm.com>) id 1SqfNI-00083a-Os
	for qemu-devel@nongnu.org; Mon, 16 Jul 2012 03:05:54 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <borntraeger@de.ibm.com>) id 1SqfNB-0002di-Ru
	for qemu-devel@nongnu.org; Mon, 16 Jul 2012 03:05:44 -0400
Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:52226)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <borntraeger@de.ibm.com>) id 1SqfNB-0002dO-JB
	for qemu-devel@nongnu.org; Mon, 16 Jul 2012 03:05:37 -0400
Received: from /spool/local
	by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use
	Only! Violators will be prosecuted
	for <qemu-devel@nongnu.org> from <borntraeger@de.ibm.com>;
	Mon, 16 Jul 2012 08:05:35 +0100
Received: from d06av03.portsmouth.uk.ibm.com (d06av03.portsmouth.uk.ibm.com
	[9.149.37.213])
	by d06nrmr1407.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with
	ESMTP id q6G74slI2420826
	for <qemu-devel@nongnu.org>; Mon, 16 Jul 2012 08:04:54 +0100
Received: from d06av03.portsmouth.uk.ibm.com (localhost.localdomain
	[127.0.0.1])
	by d06av03.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with
	ESMTP id q6G74rIR003720
	for <qemu-devel@nongnu.org>; Mon, 16 Jul 2012 01:04:53 -0600
Message-ID: <5003BD14.2090709@de.ibm.com>
Date: Mon, 16 Jul 2012 09:04:52 +0200
From: Christian Borntraeger <borntraeger@de.ibm.com>
MIME-Version: 1.0
References: <1342176724-43776-1-git-send-email-borntraeger@de.ibm.com>
	<1342176724-43776-3-git-send-email-borntraeger@de.ibm.com>
	<CAAu8pHuEAt09ZLhzY-Jux4gxYC2NkG=u+2jcHESUCDnGGjcJEg@mail.gmail.com>
	<50005058.6000707@de.ibm.com>
	<CAAu8pHsN=Fa8WNgCyoEBkWZ2xiozZoEo=q8T2iXUnKvX0wDgAA@mail.gmail.com>
In-Reply-To: <CAAu8pHsN=Fa8WNgCyoEBkWZ2xiozZoEo=q8T2iXUnKvX0wDgAA@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 2/6] s390: sclp base support
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: Blue Swirl <blauwirbel@gmail.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>, Jens Freimann <jfrei@linux.vnet.ibm.com>, Heinz Graalfs <graalfs@linux.vnet.ibm.com>, Alexander Graf <agraf@suse.de>, qemu-devel <qemu-devel@nongnu.org>

On 14/07/12 10:48, Blue Swirl wrote:
>>>> +    cpu_physical_memory_write(sccb, &work_sccb,
>>>> +                              be16_to_cpu(work_sccb.h.length));
>>>
>>> Perhaps the DMA helpers should be used instead.
>>>
>>
>> Is there any rule what to use under which circumstances.
> 
> No, it's a recent addition. Devices (at least those which may be used
> in IOMMU environment) should use DMA helpers for their memory accesses
> in general but virtio may be an exception. I'm not sure which category
> this falls in.

Ok, I read this as, if we need to handle DMA into virtual addresses at some
point in time dma helpers are the way to go.

With SCLP we access real storage (no translation) so I think 
cpu_physical_memory_write is fine here. 

Christian