[PATCH v6 1/2] docs: s390/pci: Improve and update PCI documentation

[Niklas Schnelle]

Update the s390 specific PCI documentation to better reflect current
behavior and terms such as the handling of Isolated VFs via commit
25f39d3dcb48 ("s390/pci: Ignore RID for isolated VFs").

Add a descriptions for /sys/firmware/clp/uid_is_unique which was added
in commit b043a81ce3ee ("s390/pci: Expose firmware provided UID Checking
state in sysfs") but missed documentation.

Similarly add documentation for the fidparm attribute added by commit
99ad39306a62 ("s390/pci: Expose FIDPARM attribute in sysfs") and
add a list of pft values and their names.

Finally improve formatting of the different attribute descriptions by
adding a separating colon.

Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
---
 Documentation/arch/s390/pci.rst | 139 +++++++++++++++++++++++++++-------------
 1 file changed, 94 insertions(+), 45 deletions(-)

diff --git a/Documentation/arch/s390/pci.rst b/Documentation/arch/s390/pci.rst
index d5755484d8e75c7bf67a350e61bbe04f0452a2fa..31c24ed5506f1fc07f89821f67a814118514f441 100644
--- a/Documentation/arch/s390/pci.rst
+++ b/Documentation/arch/s390/pci.rst
@@ -6,6 +6,7 @@ S/390 PCI
 
 Authors:
         - Pierre Morel
+        - Niklas Schnelle
 
 Copyright, IBM Corp. 2020
 
@@ -27,7 +28,8 @@ Command line parameters
 debugfs entries
 ---------------
 
-The S/390 debug feature (s390dbf) generates views to hold various debug results in sysfs directories of the form:
+The S/390 debug feature (s390dbf) generates views to hold various debug results
+in sysfs directories of the form:
 
  * /sys/kernel/debug/s390dbf/pci_*/
 
@@ -47,87 +49,134 @@ Sysfs entries
 
 Entries specific to zPCI functions and entries that hold zPCI information.
 
-* /sys/bus/pci/slots/XXXXXXXX
+* /sys/bus/pci/slots/XXXXXXXX:
 
-  The slot entries are set up using the function identifier (FID) of the
-  PCI function. The format depicted as XXXXXXXX above is 8 hexadecimal digits
-  with 0 padding and lower case hexadecimal digits.
+  The slot entries are set up using the function identifier (FID) of the PCI
+  function as slot name. The format depicted as XXXXXXXX above is 8 hexadecimal
+  digits with 0 padding and lower case hexadecimal digits.
 
   - /sys/bus/pci/slots/XXXXXXXX/power
 
   A physical function that currently supports a virtual function cannot be
   powered off until all virtual functions are removed with:
-  echo 0 > /sys/bus/pci/devices/XXXX:XX:XX.X/sriov_numvf
+  echo 0 > /sys/bus/pci/devices/DDDD:BB:dd.f/sriov_numvf
 
-* /sys/bus/pci/devices/XXXX:XX:XX.X/
+* /sys/bus/pci/devices/DDDD:BB:dd.f/:
 
-  - function_id
-    A zPCI function identifier that uniquely identifies the function in the Z server.
+  - function_id:
+    The zPCI function identifier (FID) is a 32 bit hexadecimal value that
+    uniquely identifies the PCI function. Unless the hypervisor provides
+    a virtual FID e.g. on KVM this identifier is unique across the machine even
+    between different partitions.
 
-  - function_handle
-    Low-level identifier used for a configured PCI function.
-    It might be useful for debugging.
+  - function_handle:
+    This 32 bit hexadecimal value is a low-level identifier used for a PCI
+    function. Note that the function handle may be changed and become invalid
+    on PCI events and when enabling/disabling the PCI function.
 
-  - pchid
-    Model-dependent location of the I/O adapter.
+  - pchid:
+    This 16 bit hexadecimal value encodes a model-dependent location for
+    the PCI function.
 
-  - pfgid
+  - pfgid:
     PCI function group ID, functions that share identical functionality
     use a common identifier.
     A PCI group defines interrupts, IOMMU, IOTLB, and DMA specifics.
 
-  - vfn
+  - vfn:
     The virtual function number, from 1 to N for virtual functions,
     0 for physical functions.
 
-  - pft
-    The PCI function type
+  - pft:
+    The PCI function type is an s390 specific type attribute. It indicates
+    a more general, usage oriented, type than PCI Specification
+    class/vendor/device identifiers. That is PCI functions with the same pft
+    value may be backed by different hardware implementations. At the same time
+    apart from unclassified functions (pft is 0x00) the same pft value
+    generally implies a similar usage model. At the same time the same
+    PCI hardware device may appear with different pft values when in a
+    different usage model. For example NETD and NETH VFs may be implemented
+    by the same PCI hardware device but in NETD the parent Physical Function
+    is user managed while with NETH it is platform managed.
 
-  - port
-    The port corresponds to the physical port the function is attached to.
-    It also gives an indication of the physical function a virtual function
-    is attached to.
+    Currently the following PFT values are defined:
 
-  - uid
-    The user identifier (UID) may be defined as part of the machine
-    configuration or the z/VM or KVM guest configuration. If the accompanying
-    uid_is_unique attribute is 1 the platform guarantees that the UID is unique
-    within that instance and no devices with the same UID can be attached
-    during the lifetime of the system.
+    - 0x00 (UNC): Unclassified
+    - 0x02 (ROCE): RoCE Express
+    - 0x05 (ISM): Internal Shared Memory
+    - 0x0a (ROC2): RoCE Express 2
+    - 0x0b (NVMe): NVMe
+    - 0x0c (NETH): Network Express hybrid
+    - 0x0d (CNW): Cloud Network Adapter
+    - 0x0f (NETD): Network Express direct
 
-  - uid_is_unique
-    Indicates whether the user identifier (UID) is guaranteed to be and remain
-    unique within this Linux instance.
+  - port:
+    The port is a decimal value corresponding to the physical port the function
+    is attached to. Virtual Functions (VFs) share the port with their parent
+    Physical Function (PF). A value of 0 indicates that the port attribute is
+    not applicable for that PCI function type.
 
-  - pfip/segmentX
+  - uid:
+    The user-defined identifier (UID) for a PCI function is a 32 bit
+    hexadecimal value. It is defined on a per instance basis as part of the
+    partition, KVM guest, or z/VM guest configuration. If UID Checking is
+    enabled the platform ensures that the UID is unique within that instance
+    and no two PCI functions with the same UID will be visible to the instance.
+
+    Independent of this guarantee and unlike the function ID (FID) the UID may
+    be the same in different partitions within the same machine. This allows to
+    create PCI configurations in multiple partitions to be identical in the
+    UID-namespace.
+
+  - uid_is_unique:
+    A 0 or 1 flag indicating whether the user-defined identifier (UID) is
+    guaranteed to be and remain unique within this Linux instance. This
+    platform feature is called UID Checking.
+
+  - pfip/segmentX:
     The segments determine the isolation of a function.
     They correspond to the physical path to the function.
     The more the segments are different, the more the functions are isolated.
 
+  - fidparm:
+    Contains an 8 bit per PCI function parameter field in hexadecimal provided
+    by the platform. The meaning of this field is PCI function type specific.
+    For NETH VFs a value of 0x01 indicates that the function supports
+    promiscuous mode.
+
+* /sys/firmware/clp/uid_is_unique:
+
+  In addition to the per-device uid_is_unique attribute this presents a
+  global indication of whether UID Checking is enabled. This allows users
+  to check for UID Checking even when no PCI functions are configured.
+
 Enumeration and hotplug
 =======================
 
 The PCI address consists of four parts: domain, bus, device and function,
-and is of this form: DDDD:BB:dd.f
+and is of this form: DDDD:BB:dd.f.
 
-* When not using multi-functions (norid is set, or the firmware does not
-  support multi-functions):
+* For a PCI function for which the platform does not expose the RID, the
+  pci=norid kernel parameter is used, or a so called isolated Virtual Function
+  which does have RID information but is used without its parent Physical
+  Function being part of the same PCI configuration:
 
   - There is only one function per domain.
 
-  - The domain is set from the zPCI function's UID as defined during the
-    LPAR creation.
+  - The domain is set from the zPCI function's UID if UID Checking is on
+    otherwise the domain ID is generated dynamically and is not stable
+    across reboots or hot plug.
 
-* When using multi-functions (norid parameter is not set),
-  zPCI functions are addressed differently:
+* For a PCI function for which the platform exposes the RID and which
+  is not an Isolated Virtual Function:
 
   - There is still only one bus per domain.
 
-  - There can be up to 256 functions per bus.
+  - There can be up to 256 PCI functions per bus.
 
-  - The domain part of the address of all functions for
-    a multi-Function device is set from the zPCI function's UID as defined
-    in the LPAR creation for the function zero.
+  - The domain part of the address of all functions within the same topology is
+    that of the configured PCI function with the lowest devfn within that
+    topology.
 
-  - New functions will only be ready for use after the function zero
-    (the function with devfn 0) has been enumerated.
+  - Virtual Functions generated by an SR-IOV capable Physical Function only
+    become visible once SR-IOV is enabled.

-- 
2.51.0