Re: [Xen-devel] Xen ARM community call - meeting minutes and date for the next one

["Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>]

On Wed, Dec 14, 2016 at 03:59:00PM +0100, Dario Faggioli wrote:
> On Tue, 2016-12-13 at 19:00 +0000, Julien Grall wrote:
> > Hi all,
> > 
> > Stefano suggested to move the call at 5pm and I haven't seen any 
> > disagreement.
> > 
> > So the call will be tomorrow (Wednesday 14th December at 5pm).


Hi all,

Thanks for the call today. I'm sending a link to EEMI the
power management framework that Xilinx co-developed with Aggios.
I don't have a link to the ARM specs for SCMI. I found some slides
though. Perhaps Julien has specs?

SCMI:
http://www.slideshare.net/linaroorg/las16200-scmi-system-management-and-control-interface

EEMI:
https://www.xilinx.com/support/documentation/user_guides/ug1200-eemi-api.pdf

Roughly, EEMI works top down by having the various SW layers request
power down/up and other settings to the layer beneath. The various
layers are responsible for recounting so that we don't shut down
something that is in use and also to isolate so that we don't
turn on or off anything that we don't own.

At the moment we tunnel API calls via SMC calls to EL3. For calls
that ATF at EL3 can implement it answers directly. If not, these
calls further propagate over a shared memory / IPI interface to
a dedicated tiny core (PMU) with power management firmware.

The PMU is responsible for mediating power/clock request changes
and making sure that the requesters don't mess with devices or
settings that don't belong to them.

So top down the idea is:

EL0  User-space uses devices (open/close or whatever).
EL1  OS/Kernel refcounts per process and requests power down/up of devs when 
not used.
EL2  Hypervisor (or dom0 or something not yet implemented) refcounts per guest 
and forwards the request down the chain if appropriate.
EL3  Trusted Firmware mediates between Normal and Secure world.

PMU  Mediates between different CPU clusters and Programmable logic.

Best regards,
Edgar





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