On Fri, Jun 26, 2020 at 7:22 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > 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. Hmm, yes I guess freeze should be sufficient to quiesce most device-DMA in the general case as applications will stop sending requests. I do expect some RDMA devices will happily keep on transmitting, but that likely will need explicit mitigation. It also appears the suspend callback for at least one RDMA device mlx5_suspend() is rather violent as it appears to fully teardown the device context, not just suspend operations. To be clear, what debug interface were you thinking I could glom onto to just trigger firmware-activate at the end of the freeze phase?
