On August 21, 2020, Mike Jones wrote:
>I am trying to understand how the Server power button in the webui
>works.
>
>As before, using raspberry pi, and I’ll leave project links at the
>end for anyone that wants to use them. Things work up to monitoring
>voltages. Note the conf project has a phosphor branch for the full
>monty.>>To reverse engineer, I setup: dbus-monitor —system > someFile.log
>
>There is a message for systemd1.Manager; member=StartUnit and best I
>can tell, somehow this gets routed to systemd to start some service
>or run some exe. I see this mentioned in the dbus transactions:
>
>"obmc-host-start@0.target”
>
>And that is in /lib/systemd/system and depends
>on obmc-host-startmin@0.target, but that does not depend on any
>service. So that is a dead end. It also depends on a reboot attempts,
>but I think that is not responsible for power on/off.
>
>Then there are chassis services, but I cannot find a link from
>obmc-host-start@0.target to objc-chassis-poweron@0.target.



>
>In this
>doc: https://github.com/openbmc/docs/blob/master/architecture/openbmc
>-systemd.md
>
>It shows:
>
>
>ls -1 /lib/systemd/system/obmc-chassis-poweron\@0.target.requires/
>op-power-start@0.service op-wait-power-on@0.service>>But when I “ls” that path, the above dependencies are not there.
>There is only a dependency on phosphor-fan-presence-tach@0.service
>
>There is some state service that lead to things with xzy paths, and I
>eventually found /run/systemd/units. These have file names starting
>with “invocation” in the names and link to GUID like nodes that don’t
>“cat” like a normal file. So I am not sure how those work. Is there
>some kernel driver that works like sysfs so that these nodes are not
>traditional files?
>
>What I am trying to understand is two things:
>
>- Interaction with the power regulator
>- Interaction with the host cpu
>
>So my hope is someone can connect the dots of the path from the dbus
>to systemd through the targets to a service executable doing the work
>so I can try to replace them with:
>
>- Something that turns the regulators on/off, with pmbus in this
>case.
>- Something that can behave like a host to keep the system happy like
>a real system.



Hi.  There is some design documentation here

https://github.com/openbmc/docs/blob/master/designs/state-management-and-external-interfaces.md

and that links to phosphor-state-manager which has a lot of the units
that kick off power and state transitions.


The op-power-start are for systems following the OpenPOWER reference
designs.  The regulators are sequenced by an external microcontroller
based on the state of a POWER_ON gpio from the BMC and a return
PGOOD to indicate the state.  There are also other op- prefixed units that
initiate the host processor initialization (after the units check that fans are
running as you found). 

There is also a watchdog that is started when the host is started and
pinged and stopped via IPMI.

If you are prototyping for a x86 system, there are alternative
power implementations where the gpio toggles to represent a
main power button push and their start cpu sequences.  I think
there are also arm systems but don't know what they are using
for host interaction.

I hope this advances your investigation and learning.

milton

>
>Mike
>
>My repos
>——————
>
>https://github.com/Proclivis/meta-pmbus-raspberrypi.git
>https://github.com/Proclivis/meta-pmbus-phosphor.git
>https://github.com/Proclivis/conf-openbmc-adi.git
>
>The monitor messages for StartUnit
>———
>
>method call time=1598039669.247458 sender=:1.48 ->
>destination=org.freedesktop.systemd1 serial=33
>path=/org/freedesktop/systemd1;
>interface=org.freedesktop.systemd1.Manager; member=StartUnit
>   string "obmc-host-start@0.target"
>   string "replace"
>method call time=1598039669.276170 sender=:1.3 ->
>destination=org.freedesktop.DBus serial=775
>path=/org/freedesktop/DBus; interface=org.freedesktop.DBus;
>member=GetConnectionUnixUser
>   string ":1.48"
>method return time=1598039669.276234 sender=org.freedesktop.DBus ->
>destination=:1.3 serial=4294967295 reply_serial=775
>   uint32 0
>method call time=1598039669.280376 sender=:1.3 ->
>destination=org.freedesktop.DBus serial=776
>path=/org/freedesktop/DBus; interface=org.freedesktop.DBus;
>member=AddMatch
>   string
>"type='signal',sender='org.freedesktop.DBus',path='/org/freedesktop/D
>Bus',interface='org.freedesktop.DBus',member='NameOwnerChanged',arg0=
>':1.48'"
>method return time=1598039669.280661 sender=org.freedesktop.DBus ->
>destination=:1.3 serial=4294967295 reply_serial=776
>method call time=1598039669.280701 sender=:1.3 ->
>destination=org.freedesktop.DBus serial=777
>path=/org/freedesktop/DBus; interface=org.freedesktop.DBus;
>member=GetNameOwner
>   string ":1.48"
>method return time=1598039669.280738 sender=org.freedesktop.DBus ->
>destination=:1.3 serial=4294967295 reply_serial=777
>   string ":1.48"
>signal time=1598039669.280774 sender=:1.3 -> destination=(null
>destination) serial=778 path=/org/freedesktop/systemd1;
>interface=org.freedesktop.systemd1.Manager; member=UnitNew
>   string "obmc-host-start@0.target"
>   object path
>"/org/freedesktop/systemd1/unit/obmc_2dhost_2dstart_400_2etarget"
>signal time=1598039669.280823 sender=:1.3 -> destination=(null
>destination) serial=779 path=/org/freedesktop/systemd1;
>interface=org.freedesktop.systemd1.Manager; member=JobNew
>   uint32 1105
>   object path "/org/freedesktop/systemd1/job/1105"
>   string "obmc-host-start@0.target"
>method return time=1598039669.280883 sender=:1.3 -> destination=:1.48
>serial=780 reply_serial=33
>   object path "/org/freedesktop/systemd1/job/1105"
>signal time=1598039669.281305 sender=:1.48 -> destination=(null
>destination) serial=34 path=/xyz/openbmc_project/state/host0;
>interface=org.freedesktop.DBus.Properties; member=PropertiesChanged
>   string "xyz.openbmc_project.State.Host"
>   array [
>      dict entry(
>         string "RequestedHostTransition"
>         variant             string
>"xyz.openbmc_project.State.Host.Transition.On"
>      )
>   ]
>   array [
>   ]