On Wed, Nov 25, 2020 at 6:43 PM Furquan Shaikh <furquan@xxxxxxxxxx> wrote: > > On Wed, Nov 25, 2020 at 8:39 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > > > On Thu, Nov 12, 2020 at 8:19 PM Furquan Shaikh <furquan@xxxxxxxxxx> wrote: > > > > > > On x86 Chromebooks, we have observed this issue for a long time now - > > > when the system is powered off or rebooted, ACPI PM is not invoked and > > > this results in PowerResource _OFF methods not being invoked for any > > > of the devices. The _OFF methods are invoked correctly in case of > > > suspend-to-idle (S0ix) and suspend-to-memory(S3). However, they do not > > > get invoked when `poweroff` or `reboot` are triggered. > > > > > > One of the differences between suspend, hibernate and shutdown paths > > > in Linux kernel is that the shutdown path does not use the typical > > > device PM phases (prepare, freeze/suspend, poweroff) as used by > > > suspend/hibernate. Instead the shutdown path makes use of > > > .shutdown_pre() and .shutdown() callbacks. > > > > > > If I understand correctly, .shutdown() has been around for a long time > > > and existed even before the PM callbacks were added. Thus, > > > pm->poweroff() and .shutdown() are supposed to be analogous and > > > consistent in the behavior. > > > > Well, not quite. > > > > ->shutdown() is expected to be a lightweight operation also suitable > > for kexec() and similar situations where ->poweroff() may not work. > > > > > This is why runtime PM is disallowed by > > > device_shutdown() before it calls .shutdown() (i.e. to keep behavior > > > consistent for both paths). However, in practice, there are > > > differences in behavior for the pm->poweroff() and .shutdown() paths > > > since the shutdown path does not execute any PM domain operations. > > > > That's correct. > > > > > Because of this difference in behavior, shutdown path never invokes > > > ACPI PM and thus the ACPI PowerResources are not turned off when the > > > system is rebooted or powered off (sleep S5). On Chromebooks, it is > > > critical to run the _OFF methods for poweroff/reboot in order to > > > ensure that the device power off sequencing requirements are met. > > > Currently, these requirements are violated which impact the > > > reliability of devices over the lifetime of the platform. > > > > > > There are a few ways in which this can be addressed: > > > > > > 1. Similar to the case of hibernation, a new > > > PMSG_POWEROFF/PM_EVENT_POWEROFF can be introduced to invoke device > > > power management phases using `dpm_suspend_start(PMSG_POWEROFF)` and > > > `dpm_suspend_end(PMSG_POWEROFF)`. However, as the shutdown path uses > > > the class/bus/driver .shutdown() callbacks, adding dpm phases for > > > poweroff complicates the order of operations. If the dpm phases are > > > run before .shutdown() callbacks, then it will result in the callbacks > > > accessing devices after they are powered off. If the .shutdown() > > > callbacks are run before dpm phases, then the pm->poweroff() calls are > > > made after the device shutdown is done. Since .shutdown() and > > > pm->poweroff() are supposed to be analogous, having both calls in the > > > shutdown path is not only redundant but also results in incorrect > > > behavior. > > > > > > 2. Another option is to update device_shutdown() to make > > > pm_domain.poweroff calls after the class/bus/driver .shutdown() is > > > done. However, this suffers from the same problem as #1 above i.e. it > > > is redundant and creates conflicting order of operations. > > > > > > 3. Third possible solution is to detach the device from the PM domain > > > after it is shutdown. Currently, device drivers perform a detach > > > operation only when the device is removed. However, in case of > > > poweroff/reboot as the device is already shutdown, detaching PM domain > > > will give it the opportunity to ensure that any power resources are > > > correctly turned off before the system shuts down. > > > > 4. Make Chromebooks call something like hibernation_platform_enter() > > on S5 entries (including reboot). > > Actually, Chromebooks do not support S4 and hence CONFIG_HIBERNATION. This doesn't matter. The ->poweroff callbacks can still be used by them (of course, that part of the current hibernation support code needs to be put under a more general Kconfig option for that, but this is a technical detail). > This is done for a number of reasons including security. Hence, I > don't think using hibernation_platform_enter() would be an option. Yes, it is an option. Having "hibernation" in the name need not mean that the given piece of code is really hibernation-specific ... > > > > > Out of these, I think #3 makes the most sense as it does not introduce > > > any conflicting operations. I verified that the following diff results > > > in _OFF methods getting invoked in both poweroff and reboot cases: > > > > This won't work for PCI devices though, only for devices in the ACPI > > PM domain, so it is not sufficient in general. > > That is true. The proposed solution only handles detaching of PM > domains. I understand your point about this not working for any > devices not part of the PM domain. The issues that we have observed in > shutdown/reboot paths have been specific to ACPI power resources > controlling the sequencing to external devices. PCI devices PM can use power resources too. For instance, this has been quite common for discrete GPUs in laptops IIRC.
