From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH 1/4] Provide simple noop dma ops Date: Fri, 30 Oct 2015 23:45:58 +0900 Message-ID: <20151030144558.GA2704@suse.de> References: <1445986131-239566-1-git-send-email-borntraeger@de.ibm.com> <1445986131-239566-2-git-send-email-borntraeger@de.ibm.com> <20151028004132.GC2805@suse.de> <563368DC.3080606@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , Andy Lutomirski , Cornelia Huck , Sebastian Ott , Paolo Bonzini , benh@kernel.crashing.org, KVM , dwmw2@infradead.org, Martin Schwidefsky , linux-s390 To: Christian Borntraeger Return-path: Received: from mx2.suse.de ([195.135.220.15]:42169 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751026AbbJ3OqE (ORCPT ); Fri, 30 Oct 2015 10:46:04 -0400 Content-Disposition: inline In-Reply-To: <563368DC.3080606@de.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Oct 30, 2015 at 01:55:56PM +0100, Christian Borntraeger wrote: > It not trivial without understanding the dma mask details. Do I read > the x86 implementation right, that it limits the dma to 32 bit? Then > we cannot collapse both implementations. Or maybe we can hide this in > dma_capable. Dont know No, DMA is not limited to 32bit on x86. Each device has its own dma_mask, and the requested address+size is checked against it. The DMA_BIT_MASK(32) check is only to there to print a warning when a 32bit capable device trys to access memory above 4GB. Joerg