From mboxrd@z Thu Jan 1 00:00:00 1970 From: robin.murphy@arm.com (Robin Murphy) Date: Fri, 21 Oct 2016 17:20:43 +0100 Subject: [PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s In-Reply-To: <20161019124932.GP9193@arm.com> References: <5cf1acbf9c42cc99e5cc0dacb50b7a92c3bd0feb.1476702234.git.robin.murphy@arm.com> <20161019124932.GP9193@arm.com> Message-ID: <7aff47c3-c794-5291-4b2a-44493f398828@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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? Robin. > > Will >