[PATCH v8 0/5] powerpc/papr_scm: Add support for reporting nvdimm health

[Vaibhav Jain]

Changes since v7 [1]:

* Addressed various review comments from Aneesh, Ira and Mpe.
* Removed the 'payload_offset' field from 'struct nd_pdsm_cmd_pkg' and
  replaced it with some reserved fields [ Aneesh ].
* Updated the doc and description for patch that fetches dimm health
  information from PHYP clarifying bit-ordering [ Mpe and Ira ].
* Updated the patch title & description for patch exporting
  'seq_buf_printf'. [ Christoph Hellwig ]
* Fix types of various newly introduced vars in papr_scm.c [ Ira ].
* Fixed a typo in 'papr_scm_pdsm.h' [ Ira ]

[1] https://lore.kernel.org/linux-nvdimm/20200519190058.257981-1-vaibhav@linux.ibm.com

---

The PAPR standard[2][4] provides mechanisms to query the health and
performance stats of an NVDIMM via various hcalls as described in
Ref[3].  Until now these stats were never available nor exposed to the
user-space tools like 'ndctl'. This is partly due to PAPR platform not
having support for ACPI and NFIT. Hence 'ndctl' is unable to query and
report the dimm health status and a user had no way to determine the
current health status of a NDVIMM.

To overcome this limitation, this patch-set updates papr_scm kernel
module to query and fetch NVDIMM health stats using hcalls described
in Ref[3].  This health and performance stats are then exposed to
userspace via sysfs and PAPR-NVDIMM-Specific-Methods(PDSM) issued by
libndctl.

These changes coupled with proposed ndtcl changes located at Ref[5]
should provide a way for the user to retrieve NVDIMM health status
using ndtcl.

Below is a sample output using proposed kernel + ndctl for PAPR NVDIMM
in a emulation environment:

 # ndctl list -DH
[
  {
    "dev":"nmem0",
    "health":{
      "health_state":"fatal",
      "shutdown_state":"dirty"
    }
  }
]

Dimm health report output on a pseries guest lpar with vPMEM or HMS
based NVDIMMs that are in perfectly healthy conditions:

 # ndctl list -d nmem0 -H
[
  {
    "dev":"nmem0",
    "health":{
      "health_state":"ok",
      "shutdown_state":"clean"
    }
  }
]

PAPR NVDIMM-Specific-Methods(PDSM)
==================================

PDSM requests are issued by vendor specific code in libndctl to
execute certain operations or fetch information from NVDIMMS. PDSMs
requests can be sent to papr_scm module via libndctl(userspace) and
libnvdimm (kernel) using the ND_CMD_CALL ioctl command which can be
handled in the dimm control function papr_scm_ndctl(). Current
patchset proposes a single PDSM to retrieve NVDIMM health, defined in
the newly introduced uapi header named 'papr_scm_pdsm.h'. Support for
more PDSMs will be added in future.

Structure of the patch-set
==========================

The patch-set starts with a doc patch documenting details of hcall
H_SCM_HEALTH. Second patch exports kernel symbol seq_buf_printf()
thats used in subsequent patches to generate sysfs attribute content.

Third patch implements support for fetching NVDIMM health information
from PHYP and partially exposing it to user-space via a NVDIMM sysfs
flag.

Fourth patches deal with implementing support for servicing PDSM
commands in papr_scm module.

Finally the last patch implements support for servicing PDSM
'PAPR_SCM_PDSM_HEALTH' that returns the NVDIMM health information to
libndctl.

References:
[2] "Power Architecture Platform Reference"
      https://en.wikipedia.org/wiki/Power_Architecture_Platform_Reference
[3] commit 58b278f568f0
     ("powerpc: Provide initial documentation for PAPR hcalls")
[4] "Linux on Power Architecture Platform Reference"
     https://members.openpowerfoundation.org/document/dl/469
[5] https://github.com/vaibhav92/ndctl/tree/papr_scm_health_v8

---
Vaibhav Jain (5):
  powerpc: Document details on H_SCM_HEALTH hcall
  seq_buf: Export seq_buf_printf
  powerpc/papr_scm: Fetch nvdimm health information from PHYP
  ndctl/papr_scm,uapi: Add support for PAPR nvdimm specific methods
  powerpc/papr_scm: Implement support for PAPR_SCM_PDSM_HEALTH

 Documentation/ABI/testing/sysfs-bus-papr-scm  |  27 ++
 Documentation/powerpc/papr_hcalls.rst         |  45 ++-
 arch/powerpc/include/uapi/asm/papr_scm_pdsm.h | 175 +++++++++
 arch/powerpc/platforms/pseries/papr_scm.c     | 363 +++++++++++++++++-
 include/uapi/linux/ndctl.h                    |   1 +
 lib/seq_buf.c                                 |   1 +
 6 files changed, 599 insertions(+), 13 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-papr-scm
 create mode 100644 arch/powerpc/include/uapi/asm/papr_scm_pdsm.h

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