On Fri, Jun 26, 2020 at 2:06 AM Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > Quoting the documentation: > > Some persistent memory devices run a firmware locally on the device / > "DIMM" to perform tasks like media management, capacity provisioning, > and health monitoring. The process of updating that firmware typically > involves a reboot because it has implications for in-flight memory > transactions. However, reboots are disruptive and at least the Intel > persistent memory platform implementation, described by the Intel ACPI > DSM specification [1], has added support for activating firmware at > runtime. > > [1]: https://docs.pmem.io/persistent-memory/ > > The approach taken is to abstract the Intel platform specific mechanism > behind a libnvdimm-generic sysfs interface. The interface could support > runtime-firmware-activation on another architecture without need to > change userspace tooling. > > The ACPI NFIT implementation involves a set of device-specific-methods > (DSMs) to 'arm' individual devices for activation and bus-level > 'trigger' method to execute the activation. Informational / enumeration > methods are also provided at the bus and device level. > > One complicating aspect of the memory device firmware activation is that > the memory controller may need to be quiesced, no memory cycles, during > the activation. While the platform has mechanisms to support holding off > in-flight DMA during the activation, the device response to that delay > is potentially undefined. The platform may reject a runtime firmware > update if, for example a PCI-E device does not support its completion > timeout value being increased to meet the activation time. Outside of > device timeouts the quiesce period may also violate application > timeouts. > > Given the above device and application timeout considerations the > implementation defaults to hooking into the suspend path to trigger the > activation, i.e. that a suspend-resume cycle (at least up to the syscore > suspend point) is required. Well, that doesn't work if the suspend method for the system is set to suspend-to-idle (for example, via /sys/power/mem_sleep), because the syscore callbacks are not invoked in that case. Also you probably don't need the device power state toggling that happens during regular suspend/resume (you may not want it even for some devices). The hibernation freeze/thaw may be a better match and there is some test support in there already that may be kind of co-opted for your use case. Cheers!
