From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lorenzo Pieralisi Subject: Re: [PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s Date: Mon, 17 Oct 2016 14:21:46 +0100 Message-ID: <20161017132146.GA26341@red-moon> References: <5cf1acbf9c42cc99e5cc0dacb50b7a92c3bd0feb.1476702234.git.robin.murphy@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <5cf1acbf9c42cc99e5cc0dacb50b7a92c3bd0feb.1476702234.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Robin Murphy Cc: will.deacon-5wv7dgnIgG8@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: iommu@lists.linux-foundation.org On Mon, Oct 17, 2016 at 12:06:20PM +0100, Robin Murphy wrote: > We now delay installing our per-bus iommu_ops until we know an SMMU has > successfully probed, as they don't serve much purpose beforehand, and > doing so also avoids fights between multiple IOMMU drivers in a single > kernel. However, the upshot of passing the return value of bus_set_iommu() > back from our probe function is that if there happens to be more than > one SMMUv3 device in a system, the second and subsequent probes will > wind up returning -EBUSY to the driver core and getting torn down again. > > There are essentially 3 cases in which bus_set_iommu() returns nonzero: > 1. The bus already has iommu_ops installed > 2. One of the add_device callbacks from the initial notifier failed > 3. Allocating or installing the notifier itself failed > > The first two are down to devices other than the SMMU in question, so > shouldn't abort an otherwise-successful SMMU probe, whilst the third is > indicative of the kind of catastrophic system failure which isn't going > to get much further anyway. Consequently, there is little harm in > ignoring the return value either way. > > CC: Lorenzo Pieralisi > Signed-off-by: Robin Murphy > --- > drivers/iommu/arm-smmu-v3.c | 11 ++++------- > 1 file changed, 4 insertions(+), 7 deletions(-) > > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c > index 15c01c3cd540..74fbef384deb 100644 > --- a/drivers/iommu/arm-smmu-v3.c > +++ b/drivers/iommu/arm-smmu-v3.c > @@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev) > of_iommu_set_ops(dev->of_node, &arm_smmu_ops); > #ifdef CONFIG_PCI > pci_request_acs(); > - ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops); > - if (ret) > - return ret; > + bus_set_iommu(&pci_bus_type, &arm_smmu_ops); > #endif > #ifdef CONFIG_ARM_AMBA > - ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops); > - if (ret) > - return ret; > + bus_set_iommu(&amba_bustype, &arm_smmu_ops); > #endif > - return bus_set_iommu(&platform_bus_type, &arm_smmu_ops); > + bus_set_iommu(&platform_bus_type, &arm_smmu_ops); > + return 0; Nit: I do not see why you would not take the same approach as the ARM SMMUv1/v2, namely checking if ops are already set and skip the call if that's the case. Anyway: Acked-by: Lorenzo Pieralisi > } > > static int arm_smmu_device_remove(struct platform_device *pdev) > -- > 1.9.1 >