iommu: Add device ATS supported capability

PCIe ATS may be disabled by platform firmware, root complex limitations,
or kernel policy even when a device advertises the ATS capability in its
PCI configuration space.

Add a new IOMMU_CAP_PCI_ATS_SUPPORTED capability to allow IOMMU drivers
to report the effective ATS decision for a device.

When this capability is true for a device, ATS may be enabled for that
device, but it does not imply that ATS is currently enabled.

A subsequent patch will extend iommufd to expose the effective ATS
status to userspace.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Author: Shameer Kolothum

drivers/iommu/amd/iommu.c

@@ -2985,6 +2985,12 @@ static bool amd_iommu_capable(struct device *dev, enum iommu_cap cap)
 
 		return amd_iommu_hd_support(iommu);
 	}
+	case IOMMU_CAP_PCI_ATS_SUPPORTED: {
+		struct iommu_dev_data *dev_data = dev_iommu_priv_get(dev);
+
+		return amd_iommu_iotlb_sup &&
+			 (dev_data->flags & AMD_IOMMU_DEVICE_FLAG_ATS_SUP);
+	}
 	default:
 		break;
 	}

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -107,6 +107,7 @@ static const char * const event_class_str[] = {
 };
 
 static int arm_smmu_alloc_cd_tables(struct arm_smmu_master *master);
+static bool arm_smmu_ats_supported(struct arm_smmu_master *master);
 
 static void parse_driver_options(struct arm_smmu_device *smmu)
 {
@@ -2494,6 +2495,8 @@ static bool arm_smmu_capable(struct device *dev, enum iommu_cap cap)
 		return true;
 	case IOMMU_CAP_DIRTY_TRACKING:
 		return arm_smmu_dbm_capable(master->smmu);
+	case IOMMU_CAP_PCI_ATS_SUPPORTED:
+		return arm_smmu_ats_supported(master);
 	default:
 		return false;
 	}

drivers/iommu/intel/iommu.c

@@ -3220,6 +3220,8 @@ static bool intel_iommu_capable(struct device *dev, enum iommu_cap cap)
 		return ecap_sc_support(info->iommu->ecap);
 	case IOMMU_CAP_DIRTY_TRACKING:
 		return ssads_supported(info->iommu);
+	case IOMMU_CAP_PCI_ATS_SUPPORTED:
+		return info->ats_supported;
 	default:
 		return false;
 	}

include/linux/iommu.h

@@ -272,6 +272,8 @@ enum iommu_cap {
 	 */
 	IOMMU_CAP_DEFERRED_FLUSH,
 	IOMMU_CAP_DIRTY_TRACKING,	/* IOMMU supports dirty tracking */
+	/* ATS is supported and may be enabled for this device */
+	IOMMU_CAP_PCI_ATS_SUPPORTED,
 };
 
 /* These are the possible reserved region types */