iommu: Separate IOMMU_DEV_FEAT_IOPF from IOMMU_DEV_FEAT_SVA

Some devices manage I/O Page Faults (IOPF) themselves instead of relying
on PCIe PRI or Arm SMMU stall. Allow their drivers to enable SVA without
mandating IOMMU-managed IOPF. The other device drivers now need to first
enable IOMMU_DEV_FEAT_IOPF before enabling IOMMU_DEV_FEAT_SVA. Enabling
IOMMU_DEV_FEAT_IOPF on its own doesn't have any effect visible to the
device driver, it is used in combination with other features.

Reviewed-by: Eric Auger <[email protected]>
Reviewed-by: Lu Baolu <[email protected]>
Signed-off-by: Jean-Philippe Brucker <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>

Author: jpbrucker

include/linux/iommu.h

@@ -156,10 +156,24 @@ struct iommu_resv_region {
 	enum iommu_resv_type	type;
 };
 
-/* Per device IOMMU features */
+/**
+ * enum iommu_dev_features - Per device IOMMU features
+ * @IOMMU_DEV_FEAT_AUX: Auxiliary domain feature
+ * @IOMMU_DEV_FEAT_SVA: Shared Virtual Addresses
+ * @IOMMU_DEV_FEAT_IOPF: I/O Page Faults such as PRI or Stall. Generally
+ *			 enabling %IOMMU_DEV_FEAT_SVA requires
+ *			 %IOMMU_DEV_FEAT_IOPF, but some devices manage I/O Page
+ *			 Faults themselves instead of relying on the IOMMU. When
+ *			 supported, this feature must be enabled before and
+ *			 disabled after %IOMMU_DEV_FEAT_SVA.
+ *
+ * Device drivers query whether a feature is supported using
+ * iommu_dev_has_feature(), and enable it using iommu_dev_enable_feature().
+ */
 enum iommu_dev_features {
-	IOMMU_DEV_FEAT_AUX,	/* Aux-domain feature */
-	IOMMU_DEV_FEAT_SVA,	/* Shared Virtual Addresses */
+	IOMMU_DEV_FEAT_AUX,
+	IOMMU_DEV_FEAT_SVA,
+	IOMMU_DEV_FEAT_IOPF,
 };
 
 #define IOMMU_PASID_INVALID	(-1U)