vfio/pci: Revert nvlink removal uAPI breakage

Revert the uAPI changes from the below commit with notice that these
regions and capabilities are no longer provided.

Fixes: b392a198 ("vfio/pci: remove vfio_pci_nvlink2")
Reported-by: NGreg Kurz <groug@kaod.org>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Reviewed-by: NGreg Kurz <groug@kaod.org>
Tested-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Message-Id: <162014341432.3807030.11054087109120670135.stgit@omen>

include/uapi/linux/vfio.h

@@ -333,10 +333,21 @@ struct vfio_region_info_cap_type {
 #define VFIO_REGION_SUBTYPE_INTEL_IGD_LPC_CFG	(3)
 
 /* 10de vendor PCI sub-types */
-/* subtype 1 was VFIO_REGION_SUBTYPE_NVIDIA_NVLINK2_RAM, don't use */
+/*
+ * NVIDIA GPU NVlink2 RAM is coherent RAM mapped onto the host address space.
+ *
+ * Deprecated, region no longer provided
+ */
+#define VFIO_REGION_SUBTYPE_NVIDIA_NVLINK2_RAM	(1)
 
 /* 1014 vendor PCI sub-types */
-/* subtype 1 was VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD, don't use */
+/*
+ * IBM NPU NVlink2 ATSD (Address Translation Shootdown) register of NPU
+ * to do TLB invalidation on a GPU.
+ *
+ * Deprecated, region no longer provided
+ */
+#define VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD	(1)
 
 /* sub-types for VFIO_REGION_TYPE_GFX */
 #define VFIO_REGION_SUBTYPE_GFX_EDID            (1)
@@ -630,9 +641,36 @@ struct vfio_device_migration_info {
  */
 #define VFIO_REGION_INFO_CAP_MSIX_MAPPABLE	3
 
-/* subtype 4 was VFIO_REGION_INFO_CAP_NVLINK2_SSATGT, don't use */
+/*
+ * Capability with compressed real address (aka SSA - small system address)
+ * where GPU RAM is mapped on a system bus. Used by a GPU for DMA routing
+ * and by the userspace to associate a NVLink bridge with a GPU.
+ *
+ * Deprecated, capability no longer provided
+ */
+#define VFIO_REGION_INFO_CAP_NVLINK2_SSATGT	4
+
+struct vfio_region_info_cap_nvlink2_ssatgt {
+	struct vfio_info_cap_header header;
+	__u64 tgt;
+};
 
-/* subtype 5 was VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD, don't use */
+/*
+ * Capability with an NVLink link speed. The value is read by
+ * the NVlink2 bridge driver from the bridge's "ibm,nvlink-speed"
+ * property in the device tree. The value is fixed in the hardware
+ * and failing to provide the correct value results in the link
+ * not working with no indication from the driver why.
+ *
+ * Deprecated, capability no longer provided
+ */
+#define VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD	5
+
+struct vfio_region_info_cap_nvlink2_lnkspd {
+	struct vfio_info_cap_header header;
+	__u32 link_speed;
+	__u32 __pad;
+};
 
 /**
  * VFIO_DEVICE_GET_IRQ_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 9,