Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756899Ab3JNRIK (ORCPT ); Mon, 14 Oct 2013 13:08:10 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:50444 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756831Ab3JNRIH (ORCPT ); Mon, 14 Oct 2013 13:08:07 -0400 Date: Mon, 14 Oct 2013 18:07:19 +0100 From: Will Deacon To: Antonios Motakis Cc: Joerg Roedel , "moderated list:ARM SMMU DRIVER" , "open list:IOMMU DRIVERS" , open list , "kvmarm@lists.cs.columbia.edu" , "tech@virtualopensystems.com" , "agraf@suse.de" , "B08248@freescale.com" Subject: Re: [PATCH 1/2] ARM: SMMU: add devices attached to the SMMU to an IOMMU group Message-ID: <20131014170719.GR10491@mudshark.cambridge.arm.com> References: <1381497887-14586-1-git-send-email-a.motakis@virtualopensystems.com> <20131014124815.GC10491@mudshark.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2645 Lines: 57 On Mon, Oct 14, 2013 at 04:13:15PM +0100, Antonios Motakis wrote: > On Mon, Oct 14, 2013 at 2:48 PM, Will Deacon wrote: > > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c > > > index 0f45a48..8b71332 100644 > > > --- a/drivers/iommu/arm-smmu.c > > > +++ b/drivers/iommu/arm-smmu.c > > > @@ -1502,6 +1502,8 @@ static int arm_smmu_add_device(struct device *dev) > > > { > > > struct arm_smmu_device *child, *parent, *smmu; > > > struct arm_smmu_master *master = NULL; > > > + struct iommu_group *group; > > > + int ret; > > > > > > spin_lock(&arm_smmu_devices_lock); > > > list_for_each_entry(parent, &arm_smmu_devices, list) { > > > @@ -1534,13 +1536,27 @@ static int arm_smmu_add_device(struct device *dev) > > > if (!master) > > > return -ENODEV; > > > > > > + group = iommu_group_get(dev); > > > > I'm not especially familiar with IOMMU groups (I understand them as the > > minimum translation granularity, which would mean single StreamID for the > > ARM SMMU), but under what circumstances would you expect to receive a > > non-NULL group here? I can't see any other code adding devices to groups > > (outside of other drivers)... > > > > You are right, only other IOMMU drivers will add a device to a group. > There was a discussion about this when I posted a similar patch for > the Exynos System MMU driver, see > http://lists.infradead.org/pipermail/linux-arm-kernel/2013-July/185675.html > > The idea is to check in the case of add_device() being called multiple > times, which is not the case most of the time, but still a sane > safeguard. Ok, but it feels a bit weird. The current code (arm_smmu_add_device) basically does a bunch of sanity checking against the DT data in order to find where the master sits in the device topology. Then it updates dev->archdata.iommu to point at the relevant SMMU instance. So, the interesting case is where the device was previously associated with a *different* IOMMU. In that case, the current code clobbers the iommu field with the new smmu, whereas the new code could end up getting very confused with respect to IOMMU groups. A better way is probably to check that dev->archdata.iommu is NULL before we assign to it. If not, then spit out a warning and return an error. That would also mean you could get rid of the group get/put calls. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/