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Persistent memory devices like NVDIMMs can loose cached writes in case something prevents flush on power-fail. Such situations are termed as dirty shutdown and are exposed to applications as last-shutdown-state (LSS) flag and a dirty-shutdown-counter(DSC) as described at [1]. The latter being useful in conditions where multiple applications want to detect a dirty shutdown event without racing with one another. PAPR-NVDIMMs have so far only exposed LSS style flags to indicate a dirty-shutdown-state. This patch further adds support for DSC via the "ibm,persistence-failed-count" device tree property of an NVDIMM. This property is a monotonic increasing 64-bit counter thats an indication of number of times an NVDIMM has encountered a dirty-shutdown event causing persistence loss. Since this value is not expected to change after system-boot hence papr_scm reads & caches its value during NVDIMM probe and exposes it as a PAPR sysfs attributed named 'dirty_shutdown' to match the name of similarly named NFIT sysfs attribute. Also this value is available to libnvdimm via PAPR_PDSM_HEALTH payload. 'struct nd_papr_pdsm_health' has been extended to add a new member called 'dimm_dsc' presence of which is indicated by the newly introduced PDSM_DIMM_DSC_VALID flag. References: [1] https://pmem.io/documents/Dirty_Shutdown_Handling-V1.0.pdf Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210624080621.252038-1-vaibhav@linux.ibm.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.