From mboxrd@z Thu Jan 1 00:00:00 1970 From: lorenzo.pieralisi@arm.com (Lorenzo Pieralisi) Date: Mon, 17 Oct 2016 18:57:48 +0100 Subject: [PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s In-Reply-To: References: <5cf1acbf9c42cc99e5cc0dacb50b7a92c3bd0feb.1476702234.git.robin.murphy@arm.com> <20161017132146.GA26341@red-moon> Message-ID: <20161017175748.GB28817@red-moon> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Oct 17, 2016 at 03:19:46PM +0100, Robin Murphy wrote: > Hi Lorenzo, > > On 17/10/16 14:21, Lorenzo Pieralisi 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; > > > > 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. > > Well, I'd say it really goes the other way around - since the very first > thing bus_set_iommu() does is check if ops are present, and return if > so, and the v2 driver already doesn't care about that return value, > there's not really any need for it to duplicate the check either. I > didn't change it at the time to avoid cluttering the gigantic rework any > further, but I could spin a cleanup patch if you like. No worries, it was to understand if there was a reason to keep the code different and after another look I agree with what you are saying (by checking if ops are present you could eg avoid calling pci_request_acs() every probe but that's a detail). Thanks for fixing it ! Lorenzo > > Anyway: > > > > Acked-by: Lorenzo Pieralisi > > Thanks! > > Robin. >