[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[sricharan@codeaurora.org (Sricharan)]

Hi,

>-----Original Message-----
>From: linux-arm-kernel [mailto:linux-arm-kernel-bounces at lists.infradead.org] On Behalf Of Robin Murphy
>Sent: Monday, October 17, 2016 4:36 PM
>To: will.deacon at arm.com; joro at 8bytes.org
>Cc: iommu at lists.linux-foundation.org; Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>; linux-arm-kernel at lists.infradead.org
>Subject: [PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s
>
>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 <lorenzo.pieralisi@arm.com>
>Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>---
> 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;
    reviewed-by: sricharan at codeaurora.org

Regards,
 Sricharan