iommu: Add new iommu op to get iommu hardware information

Introduce a new iommu op to get the IOMMU hardware capabilities for
iommufd. This information will be used by any vIOMMU driver which is owned
by userspace.

This op chooses to make the special parameters opaque to the core. This
suits the current usage model where accessing any of the IOMMU device
special parameters does require a userspace driver that matches the kernel
driver. If a need for common parameters, implemented similarly by several
drivers, arises then there's room in the design to grow a generic
parameter set as well. No wrapper API is added as it is supposed to be
used by iommufd only.

Different IOMMU hardware would have different hardware information. So the
information reported differs as well. To let the external user understand
the difference, enum iommu_hw_info_type is defined. For the iommu drivers
that are capable to report hardware information, it should have a unique
iommu_hw_info_type and return to caller. For the driver doesn't report
hardware information, caller just uses IOMMU_HW_INFO_TYPE_NONE if a type
is required.

Link: https://lore.kernel.org/r/20230818101033.4100-3-yi.l.liu@intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Co-developed-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

include/uapi/linux/iommufd.h

@@ -370,4 +370,13 @@ struct iommu_hwpt_alloc {
 	__u32 __reserved;
 };
 #define IOMMU_HWPT_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_HWPT_ALLOC)
+
+/**
+ * enum iommu_hw_info_type - IOMMU Hardware Info Types
+ * @IOMMU_HW_INFO_TYPE_NONE: Used by the drivers that do not report hardware
+ *                           info
+ */
+enum iommu_hw_info_type {
+	IOMMU_HW_INFO_TYPE_NONE,
+};
 #endif