From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s Date: Wed, 26 Oct 2016 10:29:24 +0100 Message-ID: <20161026092850.GC2104@arm.com> References: <5cf1acbf9c42cc99e5cc0dacb50b7a92c3bd0feb.1476702234.git.robin.murphy@arm.com> <20161019124932.GP9193@arm.com> <7aff47c3-c794-5291-4b2a-44493f398828@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: <7aff47c3-c794-5291-4b2a-44493f398828-5wv7dgnIgG8@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: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: iommu@lists.linux-foundation.org On Fri, Oct 21, 2016 at 05:20:43PM +0100, Robin Murphy wrote: > On 19/10/16 13:49, Will Deacon wrote: > > 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; > > > > In which case, we should probably add an iommu_present check, like we > > have for the v2 driver. > > As touched upon in the commit message, the first thing bus_set_iommu() > does is perform that same check and return immediately if any ops are > already set. Do you really want redundant checks added, or shall I spin > that cleanup patch removing them from v2 that I proposed to Lorenzo? A cleanup patch sounds good, to keep the two drivers consistent. Will