12v slot AC Support in x86-power-control

Patrick Williams patrick at stwcx.xyz
Fri Oct 9 03:31:49 AEDT 2020

On Thu, Oct 08, 2020 at 01:13:49PM +0000, P. Priyatharshan wrote:
> Out platform is multi host system and we  have the host as FRU and it can be plugged in to a slot. The slot has an option to control slot power and this can be used for a AC cycle.


I'm still very confused by the word "AC" here.  I know your server
doesn't have a single joule of AC power on any voltage rail.  This
server plugs into an OCP rack with a 12V DC bus-bar powering all the
servers in the rack.

Vijay implemented, for Tiogapass, the 12V system power cycle.  This,
in hardware, uses the HSC* to remove the server from the bus-bar, which
power cycles the entire server including the BMC.  This is as if someone
physically pulled the server from the rack and then pushed it back in
but implemented via the HSC.

On the server you are working on, we should have that same design for
the "full system power cycle" which interacts with the HSC.  This should
be done the same way as what Vijay implemented.

You also have power control to the multi-host cards which feed 12V to
each of the compute cards in your chassis.  What I don't understand is
why does this also need control of the full 12V and why is it separate
from the normal "power on the compute card" sequence?  This "power on
the compute card" sequence is what is suppose to be modelled by the
'chassisN' objects referenced by others.

Can you expand on what the difference is and what functionality you are
enabling by having two different slot-level power controls?

> We proposed  a design to add the slot power control in the x86-power-control.The earlier discussion can be found in the below link.
> https://lists.ozlabs.org/pipermail/openbmc/2020-August/022481.html

* - HSC = Hot Swap Controller.

Patrick Williams
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