.. SPDX-License-Identifier: GPL-2.0

=========
S/390 PCI
=========

Authors:
        - Pierre Morel

Copyright, IBM Corp. 2020


command line parameters and debugfs entries
===========================================

Command line parameters
-----------------------

* nomio

  Do not use MIO instructions.

* norid

  Ignore the RID field and force use of one PCI domain per PCI function.

debugfs entries
---------------

* /sys/kernel/debug/s390dbf/pci_*/ (S/390 debug feature)

  Some views generated by the debug feature to hold various debug outputs.

  - /sys/kernel/debug/s390dbf/pci_msg/sprintf
    Messages from the processing of PCI events like machine check handling
    and setting of global functionality like UID checking.

  The level of logging can be changed to be more or less verbose by piping to
  /sys/kernel/debug/s390dbf/pci_*/level a number between 0 and 6; see the
  documentation on the S/390 debug feature (Documentation/s390/s390dbf.rst)
  for details.

Sysfs entries
=============

Specific entries, or entries specificities for zPCI functions.

* /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 digitis.

  - /sys/bus/pci/slots/XXXXXXXX/power

  A physical function currently supporting virtual function can not be
  powered-off until all virtual-function have been removed with
  echo 0 > /sys/bus/pci/devices/XXXX:XX:XX.X/sriov_numvf

* /sys/bus/pci/devices/XXXX:XX:XX.X/

  - function_id
    zPCI function identifier unique for the complete Z System.
    It define uniquely a function in the system.

  - function_handle
    Low level identifier used for a configured PCI function.
    It may be useful for debuging.

  - pchid
    Model dependent location of the I/O adapter.

  - pfgid
    PCI Function Group ID, functions sharing identical functionality
    are using a common identifier.
    A PCI group defines interrupts, IOMMU, IOTLB and DMA specifics.

  - vfn
    The Virtual Function Number, from 1 to N for virtual functions.
    0 for physical functions.

  - pft
    PCI function type specifies the type of the PCI function.

  - port
    The port correspond to the physical port the function is attached to.
    It also gives an indication on the physical function a virtual function
    is attached to.

  - 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.

  - uid_is_unique
    Indicates whether the user identifier (UID) is guaranteed to be and remain
    unique within this Linux instance.

  - pfip/segmentX
    The segments are used to determine the isolation of a function.
    They corresponds to the physical path to the function.
    The more the segment are different the more the functions are isolated.

Enumeration and hotplug
=======================

The PCI address is made of 4 parts: domain, bus, device and function,
like in DDDD:BB:dd.f

* When not using multi-functions (norid is set or firmware does not support
  multi-functions)

  - There is only one function per domain.

  - the domain is set from the zPCI function's UID as defined during the
    LPAR creation.

  - Addresses look like DDDD:00:00.0

* When using multi-functions (norid parameter is not set), there are some
  change in the way zPCI functions are addressed:

  - There is still only one bus per domain.

  - There can be up to 256 functions per bus.

  - The domain part of the address of all functions 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.

  - New functions will only be ready to be used after the function zero
    (the function with devfn 0) has been enumerated.