[...] > > > >> > >> In all honesty, I am a bit surprised that the Linux device driver model > >> does not try to default the absence of a ->shutdown() to a ->suspend() > >> call since in most cases they are functionally equivalent, or should be, > >> in that they need to save power and quiesce the hardware, or leave > >> enough running to support a wake-up event. > > > > Well, the generall assumption is that the platform is going to be > > entirely powered off, thus moving things into a low power state would > > just be a waste of execution cycles. Of course, that's not the case > > for your platform. > > That assumption may hold true for ACPI-enabled machines but power off is > offered as a general function towards other more flexible and snowflaky > systems (read embedded) as well. > > > > > As I have stated earlier, to me it looks a bit questionable to use the > > kernel_power_off() path to support the use case you describe. On the > > other hand, we may not have a better option at this point. > > Correct, there is not really anything better and I am not sure what the > semantics of something better could be anyway. > > > > > Just a few things, from the top of my head, that we certainly are > > missing to support your use case through kernel_power_off() path > > (there are certainly more): > > 1. In general, subsystems/drivers don't care about moving things into > > lower power modes from their ->shutdown() callbacks. > > 2. System wakeups and devices being affected in the wakeup path, needs > > to be respected properly. Additionally, userspace should be able to > > decide if system wakeups should be enabled or not. > > 3. PM domains don't have ->shutdown() callbacks, thus it's likely that > > they remain powered on. > > 4. Etc... > > For the particular eMMC driver being discussed here this is a no-brainer > because it is not a wake-up source, therefore there is no reason not to > power if off if we can. It also seems proper to have it done by the > kernel as opposed to firmware. Okay, I have applied the $subject patch onto my next branch, along with patch 1/2 (the DT doc change). However, I still think we should look for a proper long term solution, because the kernel_power_off() path does not currently support your use case, with system wakeups etc. I guess it could be a topic that is easier to bring up at the Linux Plumbers Conf, for example. Kind regards Uffe
