87 lines
3.7 KiB
ReStructuredText
87 lines
3.7 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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==================================
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NVDIMM Runtime Firmware Activation
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==================================
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Some persistent memory devices run a firmware locally on the device /
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"DIMM" to perform tasks like media management, capacity provisioning,
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and health monitoring. The process of updating that firmware typically
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involves a reboot because it has implications for in-flight memory
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transactions. However, reboots are disruptive and at least the Intel
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persistent memory platform implementation, described by the Intel ACPI
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DSM specification [1], has added support for activating firmware at
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runtime.
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A native sysfs interface is implemented in libnvdimm to allow platform
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to advertise and control their local runtime firmware activation
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capability.
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The libnvdimm bus object, ndbusX, implements an ndbusX/firmware/activate
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attribute that shows the state of the firmware activation as one of 'idle',
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'armed', 'overflow', and 'busy'.
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- idle:
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No devices are set / armed to activate firmware
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- armed:
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At least one device is armed
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- busy:
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In the busy state armed devices are in the process of transitioning
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back to idle and completing an activation cycle.
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- overflow:
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If the platform has a concept of incremental work needed to perform
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the activation it could be the case that too many DIMMs are armed for
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activation. In that scenario the potential for firmware activation to
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timeout is indicated by the 'overflow' state.
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The 'ndbusX/firmware/activate' property can be written with a value of
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either 'live', or 'quiesce'. A value of 'quiesce' triggers the kernel to
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run firmware activation from within the equivalent of the hibernation
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'freeze' state where drivers and applications are notified to stop their
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modifications of system memory. A value of 'live' attempts
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firmware activation without this hibernation cycle. The
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'ndbusX/firmware/activate' property will be elided completely if no
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firmware activation capability is detected.
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Another property 'ndbusX/firmware/capability' indicates a value of
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'live' or 'quiesce', where 'live' indicates that the firmware
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does not require or inflict any quiesce period on the system to update
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firmware. A capability value of 'quiesce' indicates that firmware does
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expect and injects a quiet period for the memory controller, but 'live'
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may still be written to 'ndbusX/firmware/activate' as an override to
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assume the risk of racing firmware update with in-flight device and
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application activity. The 'ndbusX/firmware/capability' property will be
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elided completely if no firmware activation capability is detected.
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The libnvdimm memory-device / DIMM object, nmemX, implements
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'nmemX/firmware/activate' and 'nmemX/firmware/result' attributes to
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communicate the per-device firmware activation state. Similar to the
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'ndbusX/firmware/activate' attribute, the 'nmemX/firmware/activate'
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attribute indicates 'idle', 'armed', or 'busy'. The state transitions
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from 'armed' to 'idle' when the system is prepared to activate firmware,
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firmware staged + state set to armed, and 'ndbusX/firmware/activate' is
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triggered. After that activation event the nmemX/firmware/result
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attribute reflects the state of the last activation as one of:
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- none:
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No runtime activation triggered since the last time the device was reset
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- success:
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The last runtime activation completed successfully.
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- fail:
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The last runtime activation failed for device-specific reasons.
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- not_staged:
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The last runtime activation failed due to a sequencing error of the
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firmware image not being staged.
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- need_reset:
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Runtime firmware activation failed, but the firmware can still be
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activated via the legacy method of power-cycling the system.
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[1]: https://docs.pmem.io/persistent-memory/
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