1.. SPDX-License-Identifier: GPL-2.0
2
3==================================
4NVDIMM Runtime Firmware Activation
5==================================
6
7Some persistent memory devices run a firmware locally on the device /
8"DIMM" to perform tasks like media management, capacity provisioning,
9and health monitoring. The process of updating that firmware typically
10involves a reboot because it has implications for in-flight memory
11transactions. However, reboots are disruptive and at least the Intel
12persistent memory platform implementation, described by the Intel ACPI
13DSM specification [1], has added support for activating firmware at
14runtime.
15
16A native sysfs interface is implemented in libnvdimm to allow platform
17to advertise and control their local runtime firmware activation
18capability.
19
20The libnvdimm bus object, ndbusX, implements an ndbusX/firmware/activate
21attribute that shows the state of the firmware activation as one of 'idle',
22'armed', 'overflow', and 'busy'.
23
24- idle:
25  No devices are set / armed to activate firmware
26
27- armed:
28  At least one device is armed
29
30- busy:
31  In the busy state armed devices are in the process of transitioning
32  back to idle and completing an activation cycle.
33
34- overflow:
35  If the platform has a concept of incremental work needed to perform
36  the activation it could be the case that too many DIMMs are armed for
37  activation. In that scenario the potential for firmware activation to
38  timeout is indicated by the 'overflow' state.
39
40The 'ndbusX/firmware/activate' property can be written with a value of
41either 'live', or 'quiesce'. A value of 'quiesce' triggers the kernel to
42run firmware activation from within the equivalent of the hibernation
43'freeze' state where drivers and applications are notified to stop their
44modifications of system memory. A value of 'live' attempts
45firmware activation without this hibernation cycle. The
46'ndbusX/firmware/activate' property will be elided completely if no
47firmware activation capability is detected.
48
49Another property 'ndbusX/firmware/capability' indicates a value of
50'live' or 'quiesce', where 'live' indicates that the firmware
51does not require or inflict any quiesce period on the system to update
52firmware. A capability value of 'quiesce' indicates that firmware does
53expect and injects a quiet period for the memory controller, but 'live'
54may still be written to 'ndbusX/firmware/activate' as an override to
55assume the risk of racing firmware update with in-flight device and
56application activity. The 'ndbusX/firmware/capability' property will be
57elided completely if no firmware activation capability is detected.
58
59The libnvdimm memory-device / DIMM object, nmemX, implements
60'nmemX/firmware/activate' and 'nmemX/firmware/result' attributes to
61communicate the per-device firmware activation state. Similar to the
62'ndbusX/firmware/activate' attribute, the 'nmemX/firmware/activate'
63attribute indicates 'idle', 'armed', or 'busy'. The state transitions
64from 'armed' to 'idle' when the system is prepared to activate firmware,
65firmware staged + state set to armed, and 'ndbusX/firmware/activate' is
66triggered. After that activation event the nmemX/firmware/result
67attribute reflects the state of the last activation as one of:
68
69- none:
70  No runtime activation triggered since the last time the device was reset
71
72- success:
73  The last runtime activation completed successfully.
74
75- fail:
76  The last runtime activation failed for device-specific reasons.
77
78- not_staged:
79  The last runtime activation failed due to a sequencing error of the
80  firmware image not being staged.
81
82- need_reset:
83  Runtime firmware activation failed, but the firmware can still be
84  activated via the legacy method of power-cycling the system.
85
86[1]: https://docs.pmem.io/persistent-memory/
87