Redfish Aggregator vs. RDE over PLDM

[Deepak Kodihalli]

On 19/11/19 4:51 AM, Richard Hanley wrote:
> *Thoughts and Questions*
> Is RDE on the open-bmc roadmap at the moment?  Are there any other 
> companies looking into adding support for RDE?  Does anyone have any 
> strong feelings on this issue?
> 
> I think that in the long term a solid implementation of RDE offers a lot 
> more flexibility than a http aggregator.  However, I'd also expect it's 
> significantly more effort to get up and running.  Hence why I am asking 
> how the community feels about this subject.
>
>
> I'm also interested in hearing what people's experience working with 
> MCTP or PLDM have been.  Has anyone here used them in production? Are 
> there any particular highlights or lowlights with the protocols?

IBM will use PLDM over MCTP (over an LPC binding) for Host - BMC 
communications (system management being shared between the Host and the 
BMC) on upcoming systems. The main motivation to switch to PLDM was 
because it fit the bill of an industry standard communications protocol 
with improvements compared to in-band IPMI. RDE was also motivation for 
us to work on implementing a PLDM stack, although RDE isn't on the 
immediate roadmap. If you're interested in looking at the existing 
PLDM/MCTP code/design docs on OpenBMC, I have some links below.

We're able to map our requirements for the in-band Host BMC 
communications path to standard PLDM mostly. We did define a set of OEM 
commands to model a file as a PLDM object (and have that transferred). 
We still need to run this by PMCI to see if it's of interest to anyone 
for standardization purposes.

I'm curious why we'd use RDE for a case where the multiple management 
controllers all do have a network stack and can parse JSON. Wouldn't 
they just implement Redfish (instead of RDE) and hence this makes a case 
for the Redfish Aggregator? Based on my reading of the RDE spec, it 
seemed to target IO adapters, for eg storage controllers, that would 
want to participate in Redfish based management, but the firmware 
running on those wouldn't implement an HTTP stack.

https://github.com/openbmc/pldm
https://github.com/openbmc/libmctp
https://github.com/openbmc/docs/blob/master/designs/pldm-stack.md
https://github.com/openbmc/docs/blob/master/designs/mctp.md

Thanks,
Deepak