Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753018Ab3JRKaB (ORCPT ); Fri, 18 Oct 2013 06:30:01 -0400 Received: from mail-pa0-f54.google.com ([209.85.220.54]:50710 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752675Ab3JRK37 (ORCPT ); Fri, 18 Oct 2013 06:29:59 -0400 MIME-Version: 1.0 X-Originating-IP: [2a01:e35:2434:4600:25c7:e66d:2918:62ac] In-Reply-To: <20131014170719.GR10491@mudshark.cambridge.arm.com> References: <1381497887-14586-1-git-send-email-a.motakis@virtualopensystems.com> <20131014124815.GC10491@mudshark.cambridge.arm.com> <20131014170719.GR10491@mudshark.cambridge.arm.com> Date: Fri, 18 Oct 2013 12:29:59 +0200 Message-ID: Subject: Re: [PATCH 1/2] ARM: SMMU: add devices attached to the SMMU to an IOMMU group From: Antonios Motakis To: Will Deacon 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" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2860 Lines: 61 On Mon, Oct 14, 2013 at 7:07 PM, Will Deacon wrote: > 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. > Good point, this is a better way to handle this. I'll respin based on this. > 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/