PLDM design proposal

PLDM design proposal

[Deepak Kodihalli]

Hi All,

I've put down some thoughts below on an initial PLDM design on OpenBMC. 
Thie structure of the document is based on the OpenBMC design template. 
Please review and let me know your feedback. Once we've had a discussion 
here on the list, I can move this to Gerrit with some more details. I'd 
say reading the MCTP proposal from Jeremy should be a precursor to 
reading this.

# PLDM Stack on OpenBMC

Author: Deepak Kodihalli <dkodihal@linux.vnet.ibm.com> <dkodihal>

## Problem Description

On OpenBMC, in-band IPMI is currently the primary industry-standard 
means of communication between the BMC and the Host firmware. We've 
started hitting some inherent limitations of IPMI on OpenPOWER servers: 
a limited number of sensors, and a lack of a generic control mechanism 
(sensors are a generic monitoring mechanism) are the major ones. There 
is a need to improve upon the communication protocol, but at the same 
time inventing a custom protocol is undesirable.

This design aims to employ Platform Level Data Model (PLDM), a standard 
application layer communication protocol defined by the DMTF. PLDM draws 
inputs from IPMI, but it overcomes most of the latter's limitations. 
PLDM is also designed to run on standard transport protocols, for e.g. 
MCTP (also designed by the DMTF). MCTP provides for a common transport 
layer over several physical channels, by defining hardware bindings. The 
solution of PLDM over MCTP also helps overcome some of the limitations 
of the hardware channels that IPMI uses.

PLDM's purpose is to enable all sorts of "inside the box communication": 
BMC - Host, BMC - BMC, BMC - Network Controller and BMC - Other (for 
e.g. sensor) devices. This design doesn't preclude enablement of 
communication channels not involving the BMC and the host.

## Background and References

PLDM is designed to be an effective interface and data model that 
provides efficient access to low-level platform inventory, monitoring, 
control, event, and data/parameters transfer functions. For example, 
temperature, voltage, or fan sensors can have a PLDM representation that 
can be used to monitor and control the platform using a set of PLDM 
messages. PLDM defines data representations and commands that abstract 
the platform management hardware.

As stated earlier, PLDM is designed for different flavors of "inside the 
box" communication. PLDM groups commands under broader functions, and 
defines separate specifications for each of these functions (also called 
PLDM "Types"). The currently defined Types (and corresponding specs) are 
: PLDM base (with associated IDs and states specs), BIOS, FRU, Platform 
monitoring and control, Firmware Update and SMBIOS. All these 
specifications are available at:

https://www.dmtf.org/standards/pmci

Some of the reasons PLDM sounds promising (some of these are advantages 
over IPMI):

- Common in-band communication protocol.

- Already existing PLDM Type specifications that cover the most common 
communication requirements. Up to 64 PLDM Types can be defined (the last 
one is OEM). At the moment, 6 are defined. Each PLDM type can house up 
to 256 PLDM commands.

- PLDM sensors are 2 bytes in length.

- PLDM introduces the concept of effecters - a control mechanism. Both 
sensors and effecters are associated to entities (similar to IPMI, 
entities cab be physical or logical), where sensors are a mechanism for 
monitoring and effecters are a mechanism for control. Effecters can be 
numeric or state based. PLDM defines commonly used entities and their 
IDs, but there 8K slots available to define OEM entities.

- PLDM allows bidirectional communication, and sending asynchronous events.

- A very active PLDM related working group in the DMTF.

The plan is to run PLDM over MCTP. MCTP is defined in a spec of its own, 
and a proposal on the MCTP design is in discussion already. There's 
going to be an intermediate PLDM over MCTP binding layer, which lets us 
send PLDM messages over MCTP. This is defined in a spec of its own, and 
the design for this binding will be proposed separately.

## Requirements

How different BMC/Host/other applications make use of PLDM messages is 
outside the scope of this requirements doc. The requirements listed here 
are related to the PLDM protocol stack and the request/response model:

- Marshalling and unmarshalling of PLDM messages, defined in various 
PLDM Type specs, must be implemented. This can of course be staged based 
on the need of specific Types and functions. Since this is just encoding 
and decoding PLDM messages, I believe there would be motivation to build 
this into a library that could be shared between BMC, host and other 
firmware stacks. The specifics of each PLDM Type (such as FRU table 
structures, sensor PDR structures, etc) are implemented by this lib.

- Mapping PLDM concepts to native OpenBMC concepts must be implemented. 
For e.g.: mapping PLDM sensors to phosphor-hwmon hosted D-Bus objects, 
mapping PLDM FRU data to D-Bus objects hosted by 
phosphor-inventory-manager, etc. The mapping shouldn't be restrictive to 
D-Bus alone (meaning it shouldn't be necessary to put objects on the Bus 
just so serve PLDM requests, a problem that exists with 
phosphor-host-ipmid today). Essentially these are platform specific PLDM 
message handlers.

- The BMC should be able to act as a PLDM responder as well as a PLDM 
requester. As a PLDM responder, the BMC can monitor/control other 
devices. As a PLDM responder, the BMC can react to PLDM messages 
directed to it via requesters in the platform, for e.g, the Host.

- As a PLDM requester, the BMC must be able to discover other PLDM 
enabled components in the platform.

- As a PLDM requester, the BMC must be able to send simultaneous 
messages to different responders, but at the same time it can issue a 
single message to a specific responder at a time.

- As a PLDM requester, the BMC must be able to handle out of order 
responses.

- As a PLDM responder, the BMC may simultaneously respond to messages 
from different requesters, but the spec doesn't mandate this. In other 
words the responder could be single-threaded.

- It should be possible to plug-in non-existent PLDM functions (these 
maybe new/existing standard Types, or OEM Types) into the PLDM stack.

## Proposed Design

The following are high level structural elements of the design:

### PLDM encode/decode libraries

This library would take a PLDM message, decode it and spit out the 
different fields of the message. Conversely, given a PLDM Type, command 
code, and the command's data fields, it would make a PLDM message. The 
thought is to design this library such that it can be used by BMC and 
the host firmware stacks, because it's the encode/decode and protocol 
piece (and not the handling of a message). I'd like to know if there's 
enough motivation to have this as a common lib. That would mean 
additional requirements such as having this as a C lib instead of C++, 
because of the runtime constraints of host firmware stacks. If there's 
not enough interest to have this as a common lib, this could just be 
part of the provider libs (see below), and it could then be written in C++.

There would be one encode/decode lib per PLDM Type. So for e.g. 
something like /usr/lib/pldm/libbase.so, /usr/lib/pldm/libfru.so, etc.

### PLDM provider libraries

These libraries would implement the platform specific handling of 
incoming PLDM requests (basically helping with the PLDM responder 
implementation, see next bullet point), so for instance they would query 
D-Bus objects (or even something like a JSON file) to fetch platform 
specific information to respond to the PLDM message. They would link 
with the encode/decode libs. Like the encode/decode libs, there would be 
one per PLDM Type (for e.g /usr/lib/pldm/providers/libfru.so).

These libraries would essentially be plug-ins. That lets someone add 
functionality for new PLDM (standard as well as OEM) Types, and it also 
lets them replace default handlers. The libraries would implement a 
"register" API to plug-in handlers for specific PLDM messages. Something 
like:

template <typename Handler, typename... args>
auto register(uint8_t type, uint8_t command, Handler handler);

This allows for providing a strongly-typed C++ handler registration 
scheme. It would also be possible to validate the parameters passed to 
the handler at compile time.

### Request/Response Model

There are two approaches that I've described here, and they correlate to 
the two options in Jeremy's MCTP design for how to notify on incoming 
PLDM messages: in-process callbacks vs D-Bus signals.

#### With in-process callbacks

In this case, there would be a single PLDM (over MCTP) daemon that 
implements both the PLDM responder and PLDM requester function. The 
daemon would link with the encode/decode libs mentioned above, and the 
MCTP lib.

The PLDM responder function would involve registering the PLDM provider 
libs on startup. The PLDM responder implementation would sit in the 
callback handler from the transport's rx. If it receives PLDM messages 
of type Request, it will route them to an appropriate handler in a 
provider lib, get the response back, and send back a PLDM response 
message via the transport's tx API. If it receives messages of type 
Response, it will put them on a "Response queue".

I think designing the BMC as a PLDM requester is interesting. We haven't 
had this with IPMI, because the BMC was typically an IPMI server. I 
envision PLDM requester functions to be spread across multiple OpenBMC 
applications (instead of a single big requester app) - based on the 
responder they're talking and the high level function they implement. 
For example, there could be an app that lets the BMC upgrade firmware 
for other devices using PLDM - this would be a generic app in the sense 
that the same set of commands might have to be run irrespective of the 
device on the other side. There could also be an app that does fan 
control on a remote device, based on sensors from that device and 
algorithms specific to that device.

The PLDM daemon would have to provide a D-Bus interface to send a PLDM 
request message. This API would be used by apps wanting to send out PLDM 
requests. If the message payload is too large, the interface could 
accept an fd (containing the message), instead of an array of bytes. The 
implementation of this would send the PLDM request message via the 
transport's tx API, and then conditionally wait on the response queue to 
have an entry that matches this request (the match is by instance id). 
The conditional wait (or something equivalent) is required because the 
app sending the PLDM message must block until getting a response back 
from the remote PLDM device.

With what's been described above, it's obvious that the responder and 
requester functions need to be able to run concurrently (this is as per 
the PLDM spec as well). The BMC can simultaneously act as a responder 
and requester. Waiting on a rx from the transport layer shouldn't block 
other BMC apps from sending PLDM messages. So this means the PLDM daemon 
would have to be multi-threaded, or maybe we can instead achieve this 
via an event loop.

#### With D-Bus signals

This lets us separate PLDM daemons from the MCTP daemon, and eliminates 
the need to handle request and response messages concurrently in the 
same daemon, at the cost of much more D-Bus traffic. The MCTP daemon 
would emit D-Bus signals describing the type of the PLDM message 
(request/response) and containing the message payload. Alternatively it 
could pass the PLDM message over a D-Bus API that the PLDM daemons would 
implement. The MCTP daemon would also implement a D-Bus API to send PLDM 
messages, as with the previous approach.

With this approach, I'd recommend two separate PLDM daemons - a 
responder daemon and a requester daemon. The responder daemon reacts to 
D-Bus signals corresponding to PLDM Request messages. It handles 
incoming requests as before. The requester daemon would react to D-Bus 
signals corresponding to PLDM response messages. It would implement the 
instance id generation, and would also implement the response queue and 
the conditional wait on that queue. It would also have to implement a 
D-Bus API to let other PLDM-enabled OpenBMC apps send PLDM requests. The 
implementation of that API would send the message to the MCTP daemon, 
and then block on the response queue to get a response back.

### Multiple requesters and responders

The PLDM spec does allow simultaneous connections between multiple 
responders/requesters. For e.g. the BMC talking to a multi-host system 
on two different physical channels. Instead of implementing this in one 
MCTP/PLDM daemon, we could spawn one daemon per physical channel.

## Impacts

Development would be required to implement the PLDM protocol, the 
request/response model, and platform specific handling. Low level design 
is required to implement the protocol specifics of each of the PLDM 
Types. Such low level design is not included in this proposal.

Design and development needs to involve potential host firmware
implementations.

## Testing

Testing can be done without having to depend on the underlying transport 
layer.

The responder function can be tested by mocking a requester and the 
transport layer: this would essentially test the protocol handling and 
platform specific handling. The requester function can be tested by 
mocking a responder: this would test the instance id handling and the 
send/receive functions.

APIs from the shared libraries can be tested via fuzzing.

Thanks,
Deepak

Re: PLDM design proposal

[Alexander Amelkin]

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13.12.2018 19:30, Deepak Kodihalli wrote:
> Hi All,
>
> I've put down some thoughts below on an initial PLDM design on OpenBMC. Thie structure of the document is based on the OpenBMC design template. Please review and let me know your feedback. Once we've had a discussion here on the list, I can move this to Gerrit with some more details. I'd say reading the MCTP proposal from Jeremy should be a precursor to reading this.
>
> # PLDM Stack on OpenBMC
Hi Deepak!

Thank you for bringing this up.

PLDM/MCTP look like a logical step in context of bringing in RedFish.

Are there any ready Linux-based tools for inband management (similar to ipmitool via /dev/ipmi0) for PLDM/MCTP?

Alexander.


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Re: PLDM design proposal

[Alexander Amelkin]

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18.12.2018 17:36, Alexander Amelkin wrote:
> 13.12.2018 19:30, Deepak Kodihalli wrote:
>> Hi All,
>>
>> I've put down some thoughts below on an initial PLDM design on OpenBMC. Thie structure of the document is based on the OpenBMC design template. Please review and let me know your feedback. Once we've had a discussion here on the list, I can move this to Gerrit with some more details. I'd say reading the MCTP proposal from Jeremy should be a precursor to reading this.
>>
>> # PLDM Stack on OpenBMC
> Hi Deepak!
>
> Thank you for bringing this up.
>
> PLDM/MCTP look like a logical step in context of bringing in RedFish.
>
> Are there any ready Linux-based tools for inband management (similar to ipmitool via /dev/ipmi0) for PLDM/MCTP?
>
Also I'd like to draw your attention to our need of keeping OpenBMC compatible with OpenPOWER Firmware for P8 family. If you're planning to switch to PLDM/MCTP for BMC-to-PNOR communications, we'd need support for that in PNOR for P8.
P8 is going to remain our main CPU until P9+ is released, but we are very interested in resolving the sensor count limit problems. We're currently developing a workaround for IPMI in context of https://github.com/openbmc/openbmc/issues/3417

Alexander.


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Re: PLDM design proposal

[Deepak Kodihalli]

On 13/12/18 10:00 PM, Deepak Kodihalli wrote:
> Hi All,
> 
> I've put down some thoughts below on an initial PLDM design on OpenBMC. 
> Thie structure of the document is based on the OpenBMC design template. 
> Please review and let me know your feedback. Once we've had a discussion 
> here on the list, I can move this to Gerrit with some more details. I'd 
> say reading the MCTP proposal from Jeremy should be a precursor to 
> reading this.
> 
> # PLDM Stack on OpenBMC
> 
> Author: Deepak Kodihalli <dkodihal@linux.vnet.ibm.com> <dkodihal>
> 
> ## Problem Description
> 
> On OpenBMC, in-band IPMI is currently the primary industry-standard 
> means of communication between the BMC and the Host firmware. We've 
> started hitting some inherent limitations of IPMI on OpenPOWER servers: 
> a limited number of sensors, and a lack of a generic control mechanism 
> (sensors are a generic monitoring mechanism) are the major ones. There 
> is a need to improve upon the communication protocol, but at the same 
> time inventing a custom protocol is undesirable.
> 
> This design aims to employ Platform Level Data Model (PLDM), a standard 
> application layer communication protocol defined by the DMTF. PLDM draws 
> inputs from IPMI, but it overcomes most of the latter's limitations. 
> PLDM is also designed to run on standard transport protocols, for e.g. 
> MCTP (also designed by the DMTF). MCTP provides for a common transport 
> layer over several physical channels, by defining hardware bindings. The 
> solution of PLDM over MCTP also helps overcome some of the limitations 
> of the hardware channels that IPMI uses.
> 
> PLDM's purpose is to enable all sorts of "inside the box communication": 
> BMC - Host, BMC - BMC, BMC - Network Controller and BMC - Other (for 
> e.g. sensor) devices. This design doesn't preclude enablement of 
> communication channels not involving the BMC and the host.
> 
> ## Background and References
> 
> PLDM is designed to be an effective interface and data model that 
> provides efficient access to low-level platform inventory, monitoring, 
> control, event, and data/parameters transfer functions. For example, 
> temperature, voltage, or fan sensors can have a PLDM representation that 
> can be used to monitor and control the platform using a set of PLDM 
> messages. PLDM defines data representations and commands that abstract 
> the platform management hardware.
> 
> As stated earlier, PLDM is designed for different flavors of "inside the 
> box" communication. PLDM groups commands under broader functions, and 
> defines separate specifications for each of these functions (also called 
> PLDM "Types"). The currently defined Types (and corresponding specs) are 
> : PLDM base (with associated IDs and states specs), BIOS, FRU, Platform 
> monitoring and control, Firmware Update and SMBIOS. All these 
> specifications are available at:
> 
> https://www.dmtf.org/standards/pmci
> 
> Some of the reasons PLDM sounds promising (some of these are advantages 
> over IPMI):
> 
> - Common in-band communication protocol.
> 
> - Already existing PLDM Type specifications that cover the most common 
> communication requirements. Up to 64 PLDM Types can be defined (the last 
> one is OEM). At the moment, 6 are defined. Each PLDM type can house up 
> to 256 PLDM commands.
> 
> - PLDM sensors are 2 bytes in length.
> 
> - PLDM introduces the concept of effecters - a control mechanism. Both 
> sensors and effecters are associated to entities (similar to IPMI, 
> entities cab be physical or logical), where sensors are a mechanism for 
> monitoring and effecters are a mechanism for control. Effecters can be 
> numeric or state based. PLDM defines commonly used entities and their 
> IDs, but there 8K slots available to define OEM entities.
> 
> - PLDM allows bidirectional communication, and sending asynchronous events.
> 
> - A very active PLDM related working group in the DMTF.
> 
> The plan is to run PLDM over MCTP. MCTP is defined in a spec of its own, 
> and a proposal on the MCTP design is in discussion already. There's 
> going to be an intermediate PLDM over MCTP binding layer, which lets us 
> send PLDM messages over MCTP. This is defined in a spec of its own, and 
> the design for this binding will be proposed separately.
> 
> ## Requirements
> 
> How different BMC/Host/other applications make use of PLDM messages is 
> outside the scope of this requirements doc. The requirements listed here 
> are related to the PLDM protocol stack and the request/response model:
> 
> - Marshalling and unmarshalling of PLDM messages, defined in various 
> PLDM Type specs, must be implemented. This can of course be staged based 
> on the need of specific Types and functions. Since this is just encoding 
> and decoding PLDM messages, I believe there would be motivation to build 
> this into a library that could be shared between BMC, host and other 
> firmware stacks. The specifics of each PLDM Type (such as FRU table 
> structures, sensor PDR structures, etc) are implemented by this lib.
> 
> - Mapping PLDM concepts to native OpenBMC concepts must be implemented. 
> For e.g.: mapping PLDM sensors to phosphor-hwmon hosted D-Bus objects, 
> mapping PLDM FRU data to D-Bus objects hosted by 
> phosphor-inventory-manager, etc. The mapping shouldn't be restrictive to 
> D-Bus alone (meaning it shouldn't be necessary to put objects on the Bus 
> just so serve PLDM requests, a problem that exists with 
> phosphor-host-ipmid today). Essentially these are platform specific PLDM 
> message handlers.
> 
> - The BMC should be able to act as a PLDM responder as well as a PLDM 
> requester. As a PLDM responder, the BMC can monitor/control other 
> devices. As a PLDM responder, the BMC can react to PLDM messages 
> directed to it via requesters in the platform, for e.g, the Host.
> 
> - As a PLDM requester, the BMC must be able to discover other PLDM 
> enabled components in the platform.
> 
> - As a PLDM requester, the BMC must be able to send simultaneous 
> messages to different responders, but at the same time it can issue a 
> single message to a specific responder at a time.
> 
> - As a PLDM requester, the BMC must be able to handle out of order 
> responses.
> 
> - As a PLDM responder, the BMC may simultaneously respond to messages 
> from different requesters, but the spec doesn't mandate this. In other 
> words the responder could be single-threaded.
> 
> - It should be possible to plug-in non-existent PLDM functions (these 
> maybe new/existing standard Types, or OEM Types) into the PLDM stack.
> 
> ## Proposed Design
> 
> The following are high level structural elements of the design:
> 
> ### PLDM encode/decode libraries
> 
> This library would take a PLDM message, decode it and spit out the 
> different fields of the message. Conversely, given a PLDM Type, command 
> code, and the command's data fields, it would make a PLDM message. The 
> thought is to design this library such that it can be used by BMC and 
> the host firmware stacks, because it's the encode/decode and protocol 
> piece (and not the handling of a message). I'd like to know if there's 
> enough motivation to have this as a common lib. That would mean 
> additional requirements such as having this as a C lib instead of C++, 
> because of the runtime constraints of host firmware stacks. If there's 
> not enough interest to have this as a common lib, this could just be 
> part of the provider libs (see below), and it could then be written in C++.
> 
> There would be one encode/decode lib per PLDM Type. So for e.g. 
> something like /usr/lib/pldm/libbase.so, /usr/lib/pldm/libfru.so, etc.
> 
> ### PLDM provider libraries
> 
> These libraries would implement the platform specific handling of 
> incoming PLDM requests (basically helping with the PLDM responder 
> implementation, see next bullet point), so for instance they would query 
> D-Bus objects (or even something like a JSON file) to fetch platform 
> specific information to respond to the PLDM message. They would link 
> with the encode/decode libs. Like the encode/decode libs, there would be 
> one per PLDM Type (for e.g /usr/lib/pldm/providers/libfru.so).
> 
> These libraries would essentially be plug-ins. That lets someone add 
> functionality for new PLDM (standard as well as OEM) Types, and it also 
> lets them replace default handlers. The libraries would implement a 
> "register" API to plug-in handlers for specific PLDM messages. Something 
> like:
> 
> template <typename Handler, typename... args>
> auto register(uint8_t type, uint8_t command, Handler handler);
> 
> This allows for providing a strongly-typed C++ handler registration 
> scheme. It would also be possible to validate the parameters passed to 
> the handler at compile time.
> 
> ### Request/Response Model
> 
> There are two approaches that I've described here, and they correlate to 
> the two options in Jeremy's MCTP design for how to notify on incoming 
> PLDM messages: in-process callbacks vs D-Bus signals.
> 
> #### With in-process callbacks
> 
> In this case, there would be a single PLDM (over MCTP) daemon that 
> implements both the PLDM responder and PLDM requester function. The 
> daemon would link with the encode/decode libs mentioned above, and the 
> MCTP lib.
> 
> The PLDM responder function would involve registering the PLDM provider 
> libs on startup. The PLDM responder implementation would sit in the 
> callback handler from the transport's rx. If it receives PLDM messages 
> of type Request, it will route them to an appropriate handler in a 
> provider lib, get the response back, and send back a PLDM response 
> message via the transport's tx API. If it receives messages of type 
> Response, it will put them on a "Response queue".
> 
> I think designing the BMC as a PLDM requester is interesting. We haven't 
> had this with IPMI, because the BMC was typically an IPMI server. I 
> envision PLDM requester functions to be spread across multiple OpenBMC 
> applications (instead of a single big requester app) - based on the 
> responder they're talking and the high level function they implement. 
> For example, there could be an app that lets the BMC upgrade firmware 
> for other devices using PLDM - this would be a generic app in the sense 
> that the same set of commands might have to be run irrespective of the 
> device on the other side. There could also be an app that does fan 
> control on a remote device, based on sensors from that device and 
> algorithms specific to that device.
> 
> The PLDM daemon would have to provide a D-Bus interface to send a PLDM 
> request message. This API would be used by apps wanting to send out PLDM 
> requests. If the message payload is too large, the interface could 
> accept an fd (containing the message), instead of an array of bytes. The 
> implementation of this would send the PLDM request message via the 
> transport's tx API, and then conditionally wait on the response queue to 
> have an entry that matches this request (the match is by instance id). 
> The conditional wait (or something equivalent) is required because the 
> app sending the PLDM message must block until getting a response back 
> from the remote PLDM device.
> 
> With what's been described above, it's obvious that the responder and 
> requester functions need to be able to run concurrently (this is as per 
> the PLDM spec as well). The BMC can simultaneously act as a responder 
> and requester. Waiting on a rx from the transport layer shouldn't block 
> other BMC apps from sending PLDM messages. So this means the PLDM daemon 
> would have to be multi-threaded, or maybe we can instead achieve this 
> via an event loop.
> 
> #### With D-Bus signals
> 
> This lets us separate PLDM daemons from the MCTP daemon, and eliminates 
> the need to handle request and response messages concurrently in the 
> same daemon, at the cost of much more D-Bus traffic. The MCTP daemon 
> would emit D-Bus signals describing the type of the PLDM message 
> (request/response) and containing the message payload. Alternatively it 
> could pass the PLDM message over a D-Bus API that the PLDM daemons would 
> implement. The MCTP daemon would also implement a D-Bus API to send PLDM 
> messages, as with the previous approach.
> 
> With this approach, I'd recommend two separate PLDM daemons - a 
> responder daemon and a requester daemon. The responder daemon reacts to 
> D-Bus signals corresponding to PLDM Request messages. It handles 
> incoming requests as before. The requester daemon would react to D-Bus 
> signals corresponding to PLDM response messages. It would implement the 
> instance id generation, and would also implement the response queue and 
> the conditional wait on that queue. It would also have to implement a 
> D-Bus API to let other PLDM-enabled OpenBMC apps send PLDM requests. The 
> implementation of that API would send the message to the MCTP daemon, 
> and then block on the response queue to get a response back.
> 
> ### Multiple requesters and responders
> 
> The PLDM spec does allow simultaneous connections between multiple 
> responders/requesters. For e.g. the BMC talking to a multi-host system 
> on two different physical channels. Instead of implementing this in one 
> MCTP/PLDM daemon, we could spawn one daemon per physical channel.
> 
> ## Impacts
> 
> Development would be required to implement the PLDM protocol, the 
> request/response model, and platform specific handling. Low level design 
> is required to implement the protocol specifics of each of the PLDM 
> Types. Such low level design is not included in this proposal.
> 
> Design and development needs to involve potential host firmware
> implementations.
> 
> ## Testing
> 
> Testing can be done without having to depend on the underlying transport 
> layer.
> 
> The responder function can be tested by mocking a requester and the 
> transport layer: this would essentially test the protocol handling and 
> platform specific handling. The requester function can be tested by 
> mocking a responder: this would test the instance id handling and the 
> send/receive functions.
> 
> APIs from the shared libraries can be tested via fuzzing.
> 
> Thanks,
> Deepak

Hi,

I received some feedback on this, and I will respond to those soon (just 
got back from vacation). Others on the To: list (people who expressed 
interest in PLDM/MCTP), would like to opine on this?

Thanks,
Deepak

Re: PLDM design proposal

[Deepak Kodihalli]

On 18/12/18 8:06 PM, Alexander Amelkin wrote:
> 13.12.2018 19:30, Deepak Kodihalli wrote:
>> Hi All,
>>
>> I've put down some thoughts below on an initial PLDM design on OpenBMC. Thie structure of the document is based on the OpenBMC design template. Please review and let me know your feedback. Once we've had a discussion here on the list, I can move this to Gerrit with some more details. I'd say reading the MCTP proposal from Jeremy should be a precursor to reading this.
>>
>> # PLDM Stack on OpenBMC
> Hi Deepak!
> 
> Thank you for bringing this up.
> 
> PLDM/MCTP look like a logical step in context of bringing in RedFish.
> 
> Are there any ready Linux-based tools for inband management (similar to ipmitool via /dev/ipmi0) for PLDM/MCTP?

I haven't found one, but I've been meaning to ask this to the relevant 
DMTF workgroup. I'll keep you posted.

> Alexander.
> 

Re: PLDM design proposal

[Deepak Kodihalli]

On 21/01/19 1:38 PM, Deepak Kodihalli wrote:
> On 18/01/19 4:29 AM, Ben Wei wrote:
>>> Please do let me know if you have additional questions. I plan to 
>>> incorporate your feedback, and I'll most likely post the next draft 
>>> on Gerrit.
>>
>> Great! Looking forward to it.

I've added this design to Gerrit: 
https://gerrit.openbmc-project.xyz/#/c/openbmc/docs/+/17592/. All of the 
feedback that I've received on the mailing list has been addressed.

Ben, regarding the concurrency aspects of the PLDM requester/responder, 
I've recommended using ASIO (sdbuplus-asio, which is based on Boost 
ASIO, lets us make asynchronous D-Bus calls) as an alternate to 
multi-theading.

Thanks,
Deepak

Re: PLDM design proposal

[Deepak Kodihalli]

On 18/01/19 4:29 AM, Ben Wei wrote:
> Thanks Deepak, just couple additional questions below.
> 
>>>> Hi All,
>>>>
>>>> I've put down some thoughts below on an initial PLDM design on OpenBMC.
>>>> The structure of the document is based on the OpenBMC design template.
>>>> Please review and let me know your feedback. Once we've had a
>>>> discussion here on the list, I can move this to Gerrit with some more
>>>> details. I'd say reading the MCTP proposal from Jeremy should be a
>>>> precursor to reading this.
>>>>
>>>> # PLDM Stack on OpenBMC
>>>>
>>>> Author: Deepak Kodihalli <mailto:dkodihal@linux.vnet.ibm.com> <dkodihal>
>>>>
>>>> ## Problem Description
>>>>
>>>> On OpenBMC, in-band IPMI is currently the primary industry-standard
>>>> means of communication between the BMC and the Host firmware. We've
>>>> started hitting some inherent limitations of IPMI on OpenPOWER servers:
>>>> a limited number of sensors, and a lack of a generic control
>>>> mechanism (sensors are a generic monitoring mechanism) are the major
>>>> ones. There is a need to improve upon the communication protocol, but
>>>> at the same time inventing a custom protocol is undesirable.
>>>>
>>>> This design aims to employ Platform Level Data Model (PLDM), a
>>>> standard application layer communication protocol defined by the
>>>> DMTF. PLDM draws inputs from IPMI, but it overcomes most of the latter's limitations.
>>>> PLDM is also designed to run on standard transport protocols, for e.g.
>>>> MCTP (also designed by the DMTF). MCTP provides for a common
>>>> transport layer over several physical channels, by defining hardware
>>>> bindings. The solution of PLDM over MCTP also helps overcome some of
>>>> the limitations of the hardware channels that IPMI uses.
>>>>
>>>> PLDM's purpose is to enable all sorts of "inside the box communication":
>>>> BMC - Host, BMC - BMC, BMC - Network Controller and BMC - Other (for
>>>> e.g. sensor) devices. This design doesn't preclude enablement of
>>>> communication channels not involving the BMC and the host.
>>>>
>>>> ## Background and References
>>>>
>>>> PLDM is designed to be an effective interface and data model that
>>>> provides efficient access to low-level platform inventory,
>>>> monitoring, control, event, and data/parameters transfer functions.
>>>> For example, temperature, voltage, or fan sensors can have a PLDM
>>>> representation that can be used to monitor and control the platform
>>>> using a set of PLDM messages. PLDM defines data representations and
>>>> commands that abstract the platform management hardware.
>>>>
>>>> As stated earlier, PLDM is designed for different flavors of "inside
>>>> the box" communication. PLDM groups commands under broader functions,
>>>> and defines separate specifications for each of these functions (also
>>>> called PLDM "Types"). The currently defined Types (and corresponding
>>>> specs) are
>>>> : PLDM base (with associated IDs and states specs), BIOS, FRU,
>>>> Platform monitoring and control, Firmware Update and SMBIOS. All
>>>> these specifications are available at:
>>>>
>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.dmtf.org_sta
>>>> ndards_pmci&d=DwICAg&c=5VD0RTtNlTh3ycd41b3MUw&r=U35IaQ-7Tnwjs7q_Fwf_b
>>>> Q&m=hfNgxW6BBJnW0LRRa3Hh2xnPH29lrZDGcvqooGTWVjc&s=qOY-dlAn__E9D7LWH6L
>>>> 16US1Sq8lsCZQX1zJv36BLN0&e=
>>>>
>>>> Some of the reasons PLDM sounds promising (some of these are
>>>> advantages over IPMI):
>>>>
>>>> - Common in-band communication protocol.
>>>>
>>>> - Already existing PLDM Type specifications that cover the most
>>>> common communication requirements. Up to 64 PLDM Types can be defined
>>>> (the last one is OEM). At the moment, 6 are defined. Each PLDM type
>>>> can house up to 256 PLDM commands.
>>>>
>>>> - PLDM sensors are 2 bytes in length.
>>>>
>>>> - PLDM introduces the concept of effecters - a control mechanism.
>>>> Both sensors and effecters are associated to entities (similar to
>>>> IPMI, entities cab be physical or logical), where sensors are a
>>>> mechanism for monitoring and effecters are a mechanism for control.
>>>> Effecters can be numeric or state based. PLDM defines commonly used
>>>> entities and their IDs, but there 8K slots available to define OEM entities.
>>>>
>>>> - PLDM allows bidirectional communication, and sending asynchronous events.
>>>>
>>>> - A very active PLDM related working group in the DMTF.
>>>>
>>>> The plan is to run PLDM over MCTP. MCTP is defined in a spec of its
>>>> own, and a proposal on the MCTP design is in discussion already.
>>>> There's going to be an intermediate PLDM over MCTP binding layer,
>>>> which lets us send PLDM messages over MCTP. This is defined in a spec
>>>> of its own, and the design for this binding will be proposed separately.
>>>>
>>>> ## Requirements
>>>>
>>>> How different BMC/Host/other applications make use of PLDM messages
>>>> is outside the scope of this requirements doc. The requirements
>>>> listed here are related to the PLDM protocol stack and the request/response model:
>>>>
>>>> - Marshalling and unmarshalling of PLDM messages, defined in various
>>>> PLDM Type specs, must be implemented. This can of course be staged
>>>> based on the need of specific Types and functions. Since this is just
>>>> encoding and decoding PLDM messages, I believe there would be
>>>> motivation to build this into a library that could be shared between
>>>> BMC, host and other firmware stacks. The specifics of each PLDM Type
>>>> (such as FRU table structures, sensor PDR structures, etc) are implemented by this lib.
>>>>
>>>> - Mapping PLDM concepts to native OpenBMC concepts must be implemented.
>>>> For e.g.: mapping PLDM sensors to phosphor-hwmon hosted D-Bus
>>>> objects, mapping PLDM FRU data to D-Bus objects hosted by
>>>> phosphor-inventory-manager, etc. The mapping shouldn't be restrictive
>>>> to D-Bus alone (meaning it shouldn't be necessary to put objects on
>>>> the Bus just so serve PLDM requests, a problem that exists with
>>>> phosphor-host-ipmid today). Essentially these are platform specific
>>>> PLDM message handlers.
>>>>
>>>> - The BMC should be able to act as a PLDM responder as well as a PLDM
>>>> requester. As a PLDM responder, the BMC can monitor/control other
>>>> devices. As a PLDM responder, the BMC can react to PLDM messages
>>>> directed to it via requesters in the platform, for e.g, the Host.
>>>>
>>>> - As a PLDM requester, the BMC must be able to discover other PLDM
>>>> enabled components in the platform.
>>>>
>>>> - As a PLDM requester, the BMC must be able to send simultaneous
>>>> messages to different responders, but at the same time it can issue a
>>>> single message to a specific responder at a time.
>>>>
>>>> - As a PLDM requester, the BMC must be able to handle out of order
>>>> responses.
>>>>
>>>> - As a PLDM responder, the BMC may simultaneously respond to messages
>>>> from different requesters, but the spec doesn't mandate this. In
>>>> other words the responder could be single-threaded.
>>>>
>>>> - It should be possible to plug-in non-existent PLDM functions (these
>>>> maybe new/existing standard Types, or OEM Types) into the PLDM stack.
>>>>
>>>> ## Proposed Design
>>>>
>>>> The following are high level structural elements of the design:
>>>>
>>>> ### PLDM encode/decode libraries
>>>>
>>>> This library would take a PLDM message, decode it and spit out the
>>>> different fields of the message. Conversely, given a PLDM Type,
>>>> command code, and the command's data fields, it would make a PLDM
>>>> message. The thought is to design this library such that it can be
>>>> used by BMC and the host firmware stacks, because it's the
>>>> encode/decode and protocol piece (and not the handling of a message).
>>>> I'd like to know if there's enough motivation to have this as a
>>>> common lib. That would mean additional requirements such as having
>>>> this as a C lib instead of C++, because of the runtime constraints of
>>>> host firmware stacks. If there's not enough interest to have this as
>>>> a common lib, this could just be part of the provider libs (see below), and it could then be written in C++.
>>>
>>>
>>> Can you elaborate a bit on the pros and cons of having PLDM library as
>>> a common C lib vs them being provider libs only?
>>
>> These two are exclusive of each other, meaning what can be common is the encoding and decoding alone. The provider libs would be platform specific. I think the main advantage of having the common piece is the BMC and every other host firmware stack needn't re-implement this part.
>> So while we should strive for this, I guess some host firmware stack might not find it usable (even if it's in C) due to other constraints.
>> These constraints might not be determinable exhaustively a priori, so the disadvantage is that I'm not sure if the common lib is worth the effort as opposed to the liberty of using something like modern C++ to code this.
>>
> 
> Great, I think having a common shared library would be nice especially if we're going to have potentially multiple daemon running linking to the shared lib.
> Also I'm wondering, would this place any constraints on the plug ins?
> For example suppose we have provider libs in libbase.so and libfru.so in C++, would other plug in modules  (e.g. libfwupdate ,libbios), do they need to be in C++ as well?

The common encode/decode libs would have to be C libs, plus any other 
constraints that commonly apply to host firmware stacks (such as limited 
dynamic memory allocations) apply to them. The provider libs, like I 
said are different than the encode/decode libs. Since they are platform 
specific, they can be implemented using whatever norms apply to a 
specific platform.

>>>>
>>>> There would be one encode/decode lib per PLDM Type. So for e.g.
>>>> something like /usr/lib/pldm/libbase.so, /usr/lib/pldm/libfru.so, etc.
>>>>
>>>> ### PLDM provider libraries
>>>>
>>>> These libraries would implement the platform specific handling of
>>>> incoming PLDM requests (basically helping with the PLDM responder
>>>> implementation, see next bullet point), so for instance they would
>>>> query D-Bus objects (or even something like a JSON file) to fetch
>>>> platform specific information to respond to the PLDM message. They
>>>> would link with the encode/decode libs. Like the encode/decode libs,
>>>> there would be one per PLDM Type (for e.g /usr/lib/pldm/providers/libfru.so).
>>>>
>>>> These libraries would essentially be plug-ins. That lets someone add
>>>> functionality for new PLDM (standard as well as OEM) Types, and it
>>>> also lets them replace default handlers. The libraries would
>>>> implement a "register" API to plug-in handlers for specific PLDM
>>>> messages. Something
>>>> like:
>>>>
>>>> template <typename Handler, typename... args> auto register(uint8_t
>>>> type, uint8_t command, Handler handler);
> One thought on this is, do you want to limit registration to Type only (e.g. a libfru),
> or open registration on command level?
> At high level I feel having 1 lib registered for a type (e.g. libfru will handle all "PLDM For FRU Data"  commands) would be very clean.
> If there are unsupported command, the lib handler would reject accordingly, and anyone can add new/modify command handler at lib.
> 
> This proposed API seems to allow multiple libraries of the same type?   e.g. libfruX.so registers  Type 4, commands 0x01, 0x05, 0x07,
> And libfruY.so has the option to register Type 4, commands 0x02, 0x04,  (or even overwrite 0x01).
> Do you want to allow  this?   (I feel it's best to just combine libFruX.so and libFruY.so  into 1 libfru.so)

I agree that overwrites should be prevented, and that in general the 
registration is per-type. Although, there might be use-cases to plug-in 
an implementation of OEM commands/extensions for an existing standard type.


>>>>
>>>> This allows for providing a strongly-typed C++ handler registration
>>>> scheme. It would also be possible to validate the parameters passed
>>>> to the handler at compile time.
>>>>
>>>> ### Request/Response Model
>>>>
>>>> There are two approaches that I've described here, and they correlate
>>>> to the two options in Jeremy's MCTP design for how to notify on
>>>> incoming PLDM messages: in-process callbacks vs D-Bus signals.
>>>>
>>>> #### With in-process callbacks
>>>>
>>>> In this case, there would be a single PLDM (over MCTP) daemon that
>>>> implements both the PLDM responder and PLDM requester function. The
>>>> daemon would link with the encode/decode libs mentioned above, and
>>>> the MCTP lib.
>>>
>>> In the case if we want to run PLDM over NCSI, do you envision having a
>>> separate NCSI daemon that also link with PLDM decode/encode lib? So in
>>> this case there'd be multiple stream of (separate) PLDM traffic.
>>
>> That's one way. Having separate daemons (linking to shared PLDM
>> libraries) per transport channel gives us greater flexibility at not too much additional cost, I think.
>>
>>>>
>>>> The PLDM responder function would involve registering the PLDM
>>>> provider libs on startup. The PLDM responder implementation would sit
>>>> in the callback handler from the transport's rx. If it receives PLDM
>>>> messages of type Request, it will route them to an appropriate
>>>> handler in a provider lib, get the response back, and send back a
>>>> PLDM response message via the transport's tx API. If it receives
>>>> messages of type Response, it will put them on a "Response queue".
>>>
>>> Do you see any needs for handler in the provider lib to communicate
>>> with other daemons?
>>
>> Yes.
>>
>> For example, PLDM sensor handler may have to query a separate
>>> sensor daemon (sensord) to get the sensor data before it can respond.
>>>
>>> If the handler needs to communicate with other daemons/applications in
>>> the system, I think this part of the design would be very similar to
>>> the "BMC as PLDM requester" design you've specified below.
>>>
>>> e.g.
>>> The response from sensord may not return right away, and the PLDM
>>> handler shouldn't block, in this case I think the handler for each PLDM type  would also need a "Request Queue"
>>> so it may queue up  incoming requests while it processes each request.
>>>
>>> Also if each PLDM Type handler needs to communicate with multiple
>>> daemons, I'm thinking having a msg_in  queue (in addition to the
>>> Request queue above) so it may receive responses back from other
>>> daemons in the system, and store PLDM IID in meta-data when
>>> communicating with other daemons so the PLDM handler can map each messages in msg_in queue to a PLDM request in Request Queue.
>>>
>>> In this case each PLDM handler would need multiple threads to handle these separate tasks.
>>
>> All this sounds reasonable to me. Implementation-wise, we might have to carefully consider multi-threading as opposed to using a single thread with ASIO/event loop.
>>
>>>>
>>>> I think designing the BMC as a PLDM requester is interesting. We
>>>> haven't had this with IPMI, because the BMC was typically an IPMI
>>>> server. I envision PLDM requester functions to be spread across
>>>> multiple OpenBMC applications (instead of a single big requester app)
>>>> - based on the responder they're talking and the high level function they implement.
>>>> For example, there could be an app that lets the BMC upgrade firmware
>>>> for other devices using PLDM - this would be a generic app in the
>>>> sense that the same set of commands might have to be run irrespective
>>>> of the device on the other side. There could also be an app that does
>>>> fan control on a remote device, based on sensors from that device and
>>>> algorithms specific to that device.
>>>>
>>>> The PLDM daemon would have to provide a D-Bus interface to send a
>>>> PLDM request message. This API would be used by apps wanting to send
>>>> out PLDM requests. If the message payload is too large, the interface
>>>> could accept an fd (containing the message), instead of an array of
>>>> bytes. The implementation of this would send the PLDM request message
>>>> via the transport's tx API, and then conditionally wait on the
>>>> response queue to have an entry that matches this request (the match is by instance id).
>>>> The conditional wait (or something equivalent) is required because
>>>> the app sending the PLDM message must block until getting a response
>>>> back from the remote PLDM device.
>>>>
>>>> With what's been described above, it's obvious that the responder and
>>>> requester functions need to be able to run concurrently (this is as
>>>> per the PLDM spec as well). The BMC can simultaneously act as a
>>>> responder and requester. Waiting on a rx from the transport layer
>>>> shouldn't block other BMC apps from sending PLDM messages. So this
>>>> means the PLDM daemon would have to be multi-threaded, or maybe we
>>>> can instead achieve this via an event loop.
>>>
>>> Do you see both Requester and Responder spawning multiple threads?
>>
>> As per the base specification, I understand that the responder and requester functions should not block each other out. The base spec says a requester terminus should wait for a response from the other end before sending a new command. The spec also says a responder may optionally be multi-threaded. So I guess the answer depends on whether we view the BMC as a single requester, or multiple virtual requesters.
>> As a responder, the BMC must definitely be able to respond to different transport channels concurrently. I'm not sure yet if concurrency is required on the same transport channel.
>>
>>> I can see them performing similar functionalities,
>>>
>>> e.g. perhaps something like this below:
>>>
>>> PLDM Requester
>>> - listens for other applications/daemons for PLDM requests, and generate and send PLDM
>>>      Requests to device (1 thread)
>>> - waits for device response,  look up original request sender via response IID and send
>>>      response back to applications/daemons (1 thread)
>>>
>>> PLDM Responder
>>>     - listens for PLDM requests from device, decode request and add it
>>> to corresponding handler's Request queue (1 thread)
>>> - each handler:
>>> 	- checks its Request Queue, process request inline (if able to) and adds response to response queue,
>>>                      If request needs data from other application, send message to other application (1 thread)
>>>               - processes incoming messages from other applications and put them to Response queue (1 thread)
>>>               - process Response queue - send response back to device
>>> (1 thread)
>>>
>>>> #### With D-Bus signals
>>>>
>>>> This lets us separate PLDM daemons from the MCTP daemon, and
>>>> eliminates the need to handle request and response messages
>>>> concurrently in the same daemon, at the cost of much more D-Bus
>>>> traffic. The MCTP daemon would emit D-Bus signals describing the type
>>>> of the PLDM message
>>>> (request/response) and containing the message payload. Alternatively
>>>> it could pass the PLDM message over a D-Bus API that the PLDM daemons
>>>> would implement. The MCTP daemon would also implement a D-Bus API to
>>>> send PLDM messages, as with the previous approach.
>>>>
>>>> With this approach, I'd recommend two separate PLDM daemons - a
>>>> responder daemon and a requester daemon. The responder daemon reacts
>>>> to D-Bus signals corresponding to PLDM Request messages. It handles
>>>> incoming requests as before. The requester daemon would react to
>>>> D-Bus signals corresponding to PLDM response messages. It would
>>>> implement the instance id generation, and would also implement the
>>>> response queue and the conditional wait on that queue. It would also
>>>> have to implement a D-Bus API to let other PLDM-enabled OpenBMC apps
>>>> send PLDM requests. The implementation of that API would send the
>>>> message to the MCTP daemon, and then block on the response queue to get a response back.
>>>
>>> Similar to previous "in-process callback" approach, the  Responder
>>> daemon may have to send D-Bus signals to other applications in order process a PLDM request?
>>
>> I was thinking the responder would make D-Bus method calls.
>>
>>> Is there a way for any daemons in the system to register a
>>> communication channel With PLDM handler?
>>
>> That's a good question. We should design an API for this.
>>
>>>> ### Multiple requesters and responders
>>>>
>>>> The PLDM spec does allow simultaneous connections between multiple
>>>> responders/requesters. For e.g. the BMC talking to a multi-host
>>>> system on two different physical channels. Instead of implementing
>>>> this in one MCTP/PLDM daemon, we could spawn one daemon per physical channel.
>>>
>>> OK I see, so in this case a daemon monitor MCTP channel would have its
>>> own PLDM handler, and a daemon monitoring NCSI channel would spawn its
>>> PLDM handler, both streams of PLDM traffic occurs independently of
>>> each other and have its own series of instance IDs.
>>>
>>>> ## Impacts
>>>>
>>>> Development would be required to implement the PLDM protocol, the
>>>> request/response model, and platform specific handling. Low level
>>>> design is required to implement the protocol specifics of each of the
>>>> PLDM Types. Such low level design is not included in this proposal.
>>>>
>>>> Design and development needs to involve potential host firmware
>>>> implementations.
>>>>
>>>> ## Testing
>>>>
>>>> Testing can be done without having to depend on the underlying
>>>> transport layer.
>>>>
>>>> The responder function can be tested by mocking a requester and the
>>>> transport layer: this would essentially test the protocol handling
>>>> and platform specific handling. The requester function can be tested
>>>> by mocking a responder: this would test the instance id handling and
>>>> the send/receive functions.
>>>>
>>>> APIs from the shared libraries can be tested via fuzzing.
>>>
>>> Thanks!
>>> -Ben
>>
>> Please do let me know if you have additional questions. I plan to incorporate your feedback, and I'll most likely post the next draft on Gerrit.
> 
> Great! Looking forward to it.
> 
> Best,
> -Ben

Thanks,
Deepak

RE: PLDM design proposal

[Ben Wei]

Thanks Deepak, just couple additional questions below.

> >> Hi All,
> >>
> >> I've put down some thoughts below on an initial PLDM design on OpenBMC.
> >> The structure of the document is based on the OpenBMC design template.
> >> Please review and let me know your feedback. Once we've had a 
> >> discussion here on the list, I can move this to Gerrit with some more 
> >> details. I'd say reading the MCTP proposal from Jeremy should be a 
> >> precursor to reading this.
> >>
> >> # PLDM Stack on OpenBMC
> >>
> >> Author: Deepak Kodihalli <mailto:dkodihal@linux.vnet.ibm.com> <dkodihal>
> >>
> >> ## Problem Description
> >>
> >> On OpenBMC, in-band IPMI is currently the primary industry-standard 
> >> means of communication between the BMC and the Host firmware. We've 
> >> started hitting some inherent limitations of IPMI on OpenPOWER servers:
> >> a limited number of sensors, and a lack of a generic control 
> >> mechanism (sensors are a generic monitoring mechanism) are the major 
> >> ones. There is a need to improve upon the communication protocol, but 
> >> at the same time inventing a custom protocol is undesirable.
> >>
> >> This design aims to employ Platform Level Data Model (PLDM), a 
> >> standard application layer communication protocol defined by the 
> >> DMTF. PLDM draws inputs from IPMI, but it overcomes most of the latter's limitations.
> >> PLDM is also designed to run on standard transport protocols, for e.g.
> >> MCTP (also designed by the DMTF). MCTP provides for a common 
> >> transport layer over several physical channels, by defining hardware 
> >> bindings. The solution of PLDM over MCTP also helps overcome some of 
> >> the limitations of the hardware channels that IPMI uses.
> >>
> >> PLDM's purpose is to enable all sorts of "inside the box communication":
> >> BMC - Host, BMC - BMC, BMC - Network Controller and BMC - Other (for 
> >> e.g. sensor) devices. This design doesn't preclude enablement of 
> >> communication channels not involving the BMC and the host.
> >>
> >> ## Background and References
> >>
> >> PLDM is designed to be an effective interface and data model that 
> >> provides efficient access to low-level platform inventory, 
> >> monitoring, control, event, and data/parameters transfer functions. 
> >> For example, temperature, voltage, or fan sensors can have a PLDM 
> >> representation that can be used to monitor and control the platform 
> >> using a set of PLDM messages. PLDM defines data representations and 
> >> commands that abstract the platform management hardware.
> >>
> >> As stated earlier, PLDM is designed for different flavors of "inside 
> >> the box" communication. PLDM groups commands under broader functions, 
> >> and defines separate specifications for each of these functions (also 
> >> called PLDM "Types"). The currently defined Types (and corresponding 
> >> specs) are
> >> : PLDM base (with associated IDs and states specs), BIOS, FRU, 
> >> Platform monitoring and control, Firmware Update and SMBIOS. All 
> >> these specifications are available at:
> >>
> >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.dmtf.org_sta
> >> ndards_pmci&d=DwICAg&c=5VD0RTtNlTh3ycd41b3MUw&r=U35IaQ-7Tnwjs7q_Fwf_b
> >> Q&m=hfNgxW6BBJnW0LRRa3Hh2xnPH29lrZDGcvqooGTWVjc&s=qOY-dlAn__E9D7LWH6L
> >> 16US1Sq8lsCZQX1zJv36BLN0&e=
> >>
> >> Some of the reasons PLDM sounds promising (some of these are 
> >> advantages over IPMI):
> >>
> >> - Common in-band communication protocol.
> >>
> >> - Already existing PLDM Type specifications that cover the most 
> >> common communication requirements. Up to 64 PLDM Types can be defined 
> >> (the last one is OEM). At the moment, 6 are defined. Each PLDM type 
> >> can house up to 256 PLDM commands.
> >>
> >> - PLDM sensors are 2 bytes in length.
> >>
> >> - PLDM introduces the concept of effecters - a control mechanism. 
> >> Both sensors and effecters are associated to entities (similar to 
> >> IPMI, entities cab be physical or logical), where sensors are a 
> >> mechanism for monitoring and effecters are a mechanism for control. 
> >> Effecters can be numeric or state based. PLDM defines commonly used 
> >> entities and their IDs, but there 8K slots available to define OEM entities.
> >>
> >> - PLDM allows bidirectional communication, and sending asynchronous events.
> >>
> >> - A very active PLDM related working group in the DMTF.
> >>
> >> The plan is to run PLDM over MCTP. MCTP is defined in a spec of its 
> >> own, and a proposal on the MCTP design is in discussion already. 
> >> There's going to be an intermediate PLDM over MCTP binding layer, 
> >> which lets us send PLDM messages over MCTP. This is defined in a spec 
> >> of its own, and the design for this binding will be proposed separately.
> >>
> >> ## Requirements
> >>
> >> How different BMC/Host/other applications make use of PLDM messages 
> >> is outside the scope of this requirements doc. The requirements 
> >> listed here are related to the PLDM protocol stack and the request/response model:
> >>
> >> - Marshalling and unmarshalling of PLDM messages, defined in various 
> >> PLDM Type specs, must be implemented. This can of course be staged 
> >> based on the need of specific Types and functions. Since this is just 
> >> encoding and decoding PLDM messages, I believe there would be 
> >> motivation to build this into a library that could be shared between 
> >> BMC, host and other firmware stacks. The specifics of each PLDM Type 
> >> (such as FRU table structures, sensor PDR structures, etc) are implemented by this lib.
> >>
> >> - Mapping PLDM concepts to native OpenBMC concepts must be implemented.
> >> For e.g.: mapping PLDM sensors to phosphor-hwmon hosted D-Bus 
> >> objects, mapping PLDM FRU data to D-Bus objects hosted by 
> >> phosphor-inventory-manager, etc. The mapping shouldn't be restrictive 
> >> to D-Bus alone (meaning it shouldn't be necessary to put objects on 
> >> the Bus just so serve PLDM requests, a problem that exists with 
> >> phosphor-host-ipmid today). Essentially these are platform specific 
> >> PLDM message handlers.
> >>
> >> - The BMC should be able to act as a PLDM responder as well as a PLDM 
> >> requester. As a PLDM responder, the BMC can monitor/control other 
> >> devices. As a PLDM responder, the BMC can react to PLDM messages 
> >> directed to it via requesters in the platform, for e.g, the Host.
> >>
> >> - As a PLDM requester, the BMC must be able to discover other PLDM 
> >> enabled components in the platform.
> >>
> >> - As a PLDM requester, the BMC must be able to send simultaneous 
> >> messages to different responders, but at the same time it can issue a 
> >> single message to a specific responder at a time.
> >>
> >> - As a PLDM requester, the BMC must be able to handle out of order 
> >> responses.
> >>
> >> - As a PLDM responder, the BMC may simultaneously respond to messages 
> >> from different requesters, but the spec doesn't mandate this. In 
> >> other words the responder could be single-threaded.
> >>
> >> - It should be possible to plug-in non-existent PLDM functions (these 
> >> maybe new/existing standard Types, or OEM Types) into the PLDM stack.
> >>
> >> ## Proposed Design
> >>
> >> The following are high level structural elements of the design:
> >>
> >> ### PLDM encode/decode libraries
> >>
> >> This library would take a PLDM message, decode it and spit out the 
> >> different fields of the message. Conversely, given a PLDM Type, 
> >> command code, and the command's data fields, it would make a PLDM 
> >> message. The thought is to design this library such that it can be 
> >> used by BMC and the host firmware stacks, because it's the 
> >> encode/decode and protocol piece (and not the handling of a message). 
> >> I'd like to know if there's enough motivation to have this as a 
> >> common lib. That would mean additional requirements such as having 
> >> this as a C lib instead of C++, because of the runtime constraints of 
> >> host firmware stacks. If there's not enough interest to have this as 
> >> a common lib, this could just be part of the provider libs (see below), and it could then be written in C++.
> > 
> > 
> > Can you elaborate a bit on the pros and cons of having PLDM library as 
> > a common C lib vs them being provider libs only?
> 
> These two are exclusive of each other, meaning what can be common is the encoding and decoding alone. The provider libs would be platform specific. I think the main advantage of having the common piece is the BMC and every other host firmware stack needn't re-implement this part. 
> So while we should strive for this, I guess some host firmware stack might not find it usable (even if it's in C) due to other constraints. 
> These constraints might not be determinable exhaustively a priori, so the disadvantage is that I'm not sure if the common lib is worth the effort as opposed to the liberty of using something like modern C++ to code this.
> 

Great, I think having a common shared library would be nice especially if we're going to have potentially multiple daemon running linking to the shared lib.
Also I'm wondering, would this place any constraints on the plug ins?  
For example suppose we have provider libs in libbase.so and libfru.so in C++, would other plug in modules  (e.g. libfwupdate ,libbios), do they need to be in C++ as well?

> >>
> >> There would be one encode/decode lib per PLDM Type. So for e.g.
> >> something like /usr/lib/pldm/libbase.so, /usr/lib/pldm/libfru.so, etc.
> >>
> >> ### PLDM provider libraries
> >>
> >> These libraries would implement the platform specific handling of 
> >> incoming PLDM requests (basically helping with the PLDM responder 
> >> implementation, see next bullet point), so for instance they would 
> >> query D-Bus objects (or even something like a JSON file) to fetch 
> >> platform specific information to respond to the PLDM message. They 
> >> would link with the encode/decode libs. Like the encode/decode libs, 
> >> there would be one per PLDM Type (for e.g /usr/lib/pldm/providers/libfru.so).
> >>
> >> These libraries would essentially be plug-ins. That lets someone add 
> >> functionality for new PLDM (standard as well as OEM) Types, and it 
> >> also lets them replace default handlers. The libraries would 
> >> implement a "register" API to plug-in handlers for specific PLDM 
> >> messages. Something
> >> like:
> >>
> >> template <typename Handler, typename... args> auto register(uint8_t 
> >> type, uint8_t command, Handler handler);
One thought on this is, do you want to limit registration to Type only (e.g. a libfru), 
or open registration on command level?  
At high level I feel having 1 lib registered for a type (e.g. libfru will handle all "PLDM For FRU Data"  commands) would be very clean.
If there are unsupported command, the lib handler would reject accordingly, and anyone can add new/modify command handler at lib.

This proposed API seems to allow multiple libraries of the same type?   e.g. libfruX.so registers  Type 4, commands 0x01, 0x05, 0x07, 
And libfruY.so has the option to register Type 4, commands 0x02, 0x04,  (or even overwrite 0x01).
Do you want to allow  this?   (I feel it's best to just combine libFruX.so and libFruY.so  into 1 libfru.so)


> >>
> >> This allows for providing a strongly-typed C++ handler registration 
> >> scheme. It would also be possible to validate the parameters passed 
> >> to the handler at compile time.
> >>
> >> ### Request/Response Model
> >>
> >> There are two approaches that I've described here, and they correlate 
> >> to the two options in Jeremy's MCTP design for how to notify on 
> >> incoming PLDM messages: in-process callbacks vs D-Bus signals.
> >>
> >> #### With in-process callbacks
> >>
> >> In this case, there would be a single PLDM (over MCTP) daemon that 
> >> implements both the PLDM responder and PLDM requester function. The 
> >> daemon would link with the encode/decode libs mentioned above, and 
> >> the MCTP lib.
> > 
> > In the case if we want to run PLDM over NCSI, do you envision having a 
> > separate NCSI daemon that also link with PLDM decode/encode lib? So in 
> > this case there'd be multiple stream of (separate) PLDM traffic.
> 
> That's one way. Having separate daemons (linking to shared PLDM
> libraries) per transport channel gives us greater flexibility at not too much additional cost, I think.
> 
> >>
> >> The PLDM responder function would involve registering the PLDM 
> >> provider libs on startup. The PLDM responder implementation would sit 
> >> in the callback handler from the transport's rx. If it receives PLDM 
> >> messages of type Request, it will route them to an appropriate 
> >> handler in a provider lib, get the response back, and send back a 
> >> PLDM response message via the transport's tx API. If it receives 
> >> messages of type Response, it will put them on a "Response queue".
> > 
> > Do you see any needs for handler in the provider lib to communicate 
> > with other daemons?
> 
> Yes.
> 
> For example, PLDM sensor handler may have to query a separate
> > sensor daemon (sensord) to get the sensor data before it can respond.
> > 
> > If the handler needs to communicate with other daemons/applications in 
> > the system, I think this part of the design would be very similar to 
> > the "BMC as PLDM requester" design you've specified below.
> > 
> > e.g.
> > The response from sensord may not return right away, and the PLDM 
> > handler shouldn't block, in this case I think the handler for each PLDM type  would also need a "Request Queue"
> > so it may queue up  incoming requests while it processes each request.
> > 
> > Also if each PLDM Type handler needs to communicate with multiple 
> > daemons, I'm thinking having a msg_in  queue (in addition to the 
> > Request queue above) so it may receive responses back from other 
> > daemons in the system, and store PLDM IID in meta-data when 
> > communicating with other daemons so the PLDM handler can map each messages in msg_in queue to a PLDM request in Request Queue.
> > 
> > In this case each PLDM handler would need multiple threads to handle these separate tasks.
> 
> All this sounds reasonable to me. Implementation-wise, we might have to carefully consider multi-threading as opposed to using a single thread with ASIO/event loop.
> 
> >>
> >> I think designing the BMC as a PLDM requester is interesting. We 
> >> haven't had this with IPMI, because the BMC was typically an IPMI 
> >> server. I envision PLDM requester functions to be spread across 
> >> multiple OpenBMC applications (instead of a single big requester app) 
> >> - based on the responder they're talking and the high level function they implement.
> >> For example, there could be an app that lets the BMC upgrade firmware 
> >> for other devices using PLDM - this would be a generic app in the 
> >> sense that the same set of commands might have to be run irrespective 
> >> of the device on the other side. There could also be an app that does 
> >> fan control on a remote device, based on sensors from that device and 
> >> algorithms specific to that device.
> >>
> >> The PLDM daemon would have to provide a D-Bus interface to send a 
> >> PLDM request message. This API would be used by apps wanting to send 
> >> out PLDM requests. If the message payload is too large, the interface 
> >> could accept an fd (containing the message), instead of an array of 
> >> bytes. The implementation of this would send the PLDM request message 
> >> via the transport's tx API, and then conditionally wait on the 
> >> response queue to have an entry that matches this request (the match is by instance id).
> >> The conditional wait (or something equivalent) is required because 
> >> the app sending the PLDM message must block until getting a response 
> >> back from the remote PLDM device.
> >>
> >> With what's been described above, it's obvious that the responder and 
> >> requester functions need to be able to run concurrently (this is as 
> >> per the PLDM spec as well). The BMC can simultaneously act as a 
> >> responder and requester. Waiting on a rx from the transport layer 
> >> shouldn't block other BMC apps from sending PLDM messages. So this 
> >> means the PLDM daemon would have to be multi-threaded, or maybe we 
> >> can instead achieve this via an event loop.
> > 
> > Do you see both Requester and Responder spawning multiple threads?
> 
> As per the base specification, I understand that the responder and requester functions should not block each other out. The base spec says a requester terminus should wait for a response from the other end before sending a new command. The spec also says a responder may optionally be multi-threaded. So I guess the answer depends on whether we view the BMC as a single requester, or multiple virtual requesters. 
> As a responder, the BMC must definitely be able to respond to different transport channels concurrently. I'm not sure yet if concurrency is required on the same transport channel.
> 
> > I can see them performing similar functionalities,
> > 
> > e.g. perhaps something like this below:
> > 
> > PLDM Requester
> > - listens for other applications/daemons for PLDM requests, and generate and send PLDM
> >     Requests to device (1 thread)
> > - waits for device response,  look up original request sender via response IID and send
> >     response back to applications/daemons (1 thread)
> > 
> > PLDM Responder
> >    - listens for PLDM requests from device, decode request and add it 
> > to corresponding handler's Request queue (1 thread)
> > - each handler:
> > 	- checks its Request Queue, process request inline (if able to) and adds response to response queue,
> >                     If request needs data from other application, send message to other application (1 thread)
> >              - processes incoming messages from other applications and put them to Response queue (1 thread)
> >              - process Response queue - send response back to device 
> > (1 thread)
> > 
> >> #### With D-Bus signals
> >>
> >> This lets us separate PLDM daemons from the MCTP daemon, and 
> >> eliminates the need to handle request and response messages 
> >> concurrently in the same daemon, at the cost of much more D-Bus 
> >> traffic. The MCTP daemon would emit D-Bus signals describing the type 
> >> of the PLDM message
> >> (request/response) and containing the message payload. Alternatively 
> >> it could pass the PLDM message over a D-Bus API that the PLDM daemons 
> >> would implement. The MCTP daemon would also implement a D-Bus API to 
> >> send PLDM messages, as with the previous approach.
> >>
> >> With this approach, I'd recommend two separate PLDM daemons - a 
> >> responder daemon and a requester daemon. The responder daemon reacts 
> >> to D-Bus signals corresponding to PLDM Request messages. It handles 
> >> incoming requests as before. The requester daemon would react to 
> >> D-Bus signals corresponding to PLDM response messages. It would 
> >> implement the instance id generation, and would also implement the 
> >> response queue and the conditional wait on that queue. It would also 
> >> have to implement a D-Bus API to let other PLDM-enabled OpenBMC apps 
> >> send PLDM requests. The implementation of that API would send the 
> >> message to the MCTP daemon, and then block on the response queue to get a response back.
> > 
> > Similar to previous "in-process callback" approach, the  Responder 
> > daemon may have to send D-Bus signals to other applications in order process a PLDM request?
> 
> I was thinking the responder would make D-Bus method calls.
> 
> > Is there a way for any daemons in the system to register a 
> > communication channel With PLDM handler?
> 
> That's a good question. We should design an API for this.
> 
> >> ### Multiple requesters and responders
> >>
> >> The PLDM spec does allow simultaneous connections between multiple 
> >> responders/requesters. For e.g. the BMC talking to a multi-host 
> >> system on two different physical channels. Instead of implementing 
> >> this in one MCTP/PLDM daemon, we could spawn one daemon per physical channel.
> > 
> > OK I see, so in this case a daemon monitor MCTP channel would have its 
> > own PLDM handler, and a daemon monitoring NCSI channel would spawn its 
> > PLDM handler, both streams of PLDM traffic occurs independently of 
> > each other and have its own series of instance IDs.
> > 
> >> ## Impacts
> >>
> >> Development would be required to implement the PLDM protocol, the 
> >> request/response model, and platform specific handling. Low level 
> >> design is required to implement the protocol specifics of each of the 
> >> PLDM Types. Such low level design is not included in this proposal.
> >>
> >> Design and development needs to involve potential host firmware 
> >> implementations.
> >>
> >> ## Testing
> >>
> >> Testing can be done without having to depend on the underlying 
> >> transport layer.
> >>
> >> The responder function can be tested by mocking a requester and the 
> >> transport layer: this would essentially test the protocol handling 
> >> and platform specific handling. The requester function can be tested 
> >> by mocking a responder: this would test the instance id handling and 
> >> the send/receive functions.
> >>
> >> APIs from the shared libraries can be tested via fuzzing.
> > 
> > Thanks!
> > -Ben
> 
> Please do let me know if you have additional questions. I plan to incorporate your feedback, and I'll most likely post the next draft on Gerrit.

Great! Looking forward to it.

Best,
-Ben

Re: PLDM design proposal

[Deepak Kodihalli]

On 13/01/19 9:39 AM, Ben Wei wrote:
> Hi Deepak,
> 
> Thanks for providing the detailed design and the background info.
> I just have some questions and comments below,


Thanks for the feedback!

>> Hi All,
>>
>> I've put down some thoughts below on an initial PLDM design on OpenBMC.
>> The structure of the document is based on the OpenBMC design template.
>> Please review and let me know your feedback. Once we've had a discussion
>> here on the list, I can move this to Gerrit with some more details. I'd
>> say reading the MCTP proposal from Jeremy should be a precursor to
>> reading this.
>>
>> # PLDM Stack on OpenBMC
>>
>> Author: Deepak Kodihalli <dkodihal@linux.vnet.ibm.com> <dkodihal>
>>
>> ## Problem Description
>>
>> On OpenBMC, in-band IPMI is currently the primary industry-standard
>> means of communication between the BMC and the Host firmware. We've
>> started hitting some inherent limitations of IPMI on OpenPOWER servers:
>> a limited number of sensors, and a lack of a generic control mechanism
>> (sensors are a generic monitoring mechanism) are the major ones. There
>> is a need to improve upon the communication protocol, but at the same
>> time inventing a custom protocol is undesirable.
>>
>> This design aims to employ Platform Level Data Model (PLDM), a standard
>> application layer communication protocol defined by the DMTF. PLDM draws
>> inputs from IPMI, but it overcomes most of the latter's limitations.
>> PLDM is also designed to run on standard transport protocols, for e.g.
>> MCTP (also designed by the DMTF). MCTP provides for a common transport
>> layer over several physical channels, by defining hardware bindings. The
>> solution of PLDM over MCTP also helps overcome some of the limitations
>> of the hardware channels that IPMI uses.
>>
>> PLDM's purpose is to enable all sorts of "inside the box communication":
>> BMC - Host, BMC - BMC, BMC - Network Controller and BMC - Other (for
>> e.g. sensor) devices. This design doesn't preclude enablement of
>> communication channels not involving the BMC and the host.
>>
>> ## Background and References
>>
>> PLDM is designed to be an effective interface and data model that
>> provides efficient access to low-level platform inventory, monitoring,
>> control, event, and data/parameters transfer functions. For example,
>> temperature, voltage, or fan sensors can have a PLDM representation that
>> can be used to monitor and control the platform using a set of PLDM
>> messages. PLDM defines data representations and commands that abstract
>> the platform management hardware.
>>
>> As stated earlier, PLDM is designed for different flavors of "inside the
>> box" communication. PLDM groups commands under broader functions, and
>> defines separate specifications for each of these functions (also called
>> PLDM "Types"). The currently defined Types (and corresponding specs) are
>> : PLDM base (with associated IDs and states specs), BIOS, FRU, Platform
>> monitoring and control, Firmware Update and SMBIOS. All these
>> specifications are available at:
>>
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.dmtf.org_standards_pmci&d=DwICAg&c=5VD0RTtNlTh3ycd41b3MUw&r=U35IaQ-7Tnwjs7q_Fwf_bQ&m=hfNgxW6BBJnW0LRRa3Hh2xnPH29lrZDGcvqooGTWVjc&s=qOY-dlAn__E9D7LWH6L16US1Sq8lsCZQX1zJv36BLN0&e=
>>
>> Some of the reasons PLDM sounds promising (some of these are advantages
>> over IPMI):
>>
>> - Common in-band communication protocol.
>>
>> - Already existing PLDM Type specifications that cover the most common
>> communication requirements. Up to 64 PLDM Types can be defined (the last
>> one is OEM). At the moment, 6 are defined. Each PLDM type can house up
>> to 256 PLDM commands.
>>
>> - PLDM sensors are 2 bytes in length.
>>
>> - PLDM introduces the concept of effecters - a control mechanism. Both
>> sensors and effecters are associated to entities (similar to IPMI,
>> entities cab be physical or logical), where sensors are a mechanism for
>> monitoring and effecters are a mechanism for control. Effecters can be
>> numeric or state based. PLDM defines commonly used entities and their
>> IDs, but there 8K slots available to define OEM entities.
>>
>> - PLDM allows bidirectional communication, and sending asynchronous events.
>>
>> - A very active PLDM related working group in the DMTF.
>>
>> The plan is to run PLDM over MCTP. MCTP is defined in a spec of its own,
>> and a proposal on the MCTP design is in discussion already. There's
>> going to be an intermediate PLDM over MCTP binding layer, which lets us
>> send PLDM messages over MCTP. This is defined in a spec of its own, and
>> the design for this binding will be proposed separately.
>>
>> ## Requirements
>>
>> How different BMC/Host/other applications make use of PLDM messages is
>> outside the scope of this requirements doc. The requirements listed here
>> are related to the PLDM protocol stack and the request/response model:
>>
>> - Marshalling and unmarshalling of PLDM messages, defined in various
>> PLDM Type specs, must be implemented. This can of course be staged based
>> on the need of specific Types and functions. Since this is just encoding
>> and decoding PLDM messages, I believe there would be motivation to build
>> this into a library that could be shared between BMC, host and other
>> firmware stacks. The specifics of each PLDM Type (such as FRU table
>> structures, sensor PDR structures, etc) are implemented by this lib.
>>
>> - Mapping PLDM concepts to native OpenBMC concepts must be implemented.
>> For e.g.: mapping PLDM sensors to phosphor-hwmon hosted D-Bus objects,
>> mapping PLDM FRU data to D-Bus objects hosted by
>> phosphor-inventory-manager, etc. The mapping shouldn't be restrictive to
>> D-Bus alone (meaning it shouldn't be necessary to put objects on the Bus
>> just so serve PLDM requests, a problem that exists with
>> phosphor-host-ipmid today). Essentially these are platform specific PLDM
>> message handlers.
>>
>> - The BMC should be able to act as a PLDM responder as well as a PLDM
>> requester. As a PLDM responder, the BMC can monitor/control other
>> devices. As a PLDM responder, the BMC can react to PLDM messages
>> directed to it via requesters in the platform, for e.g, the Host.
>>
>> - As a PLDM requester, the BMC must be able to discover other PLDM
>> enabled components in the platform.
>>
>> - As a PLDM requester, the BMC must be able to send simultaneous
>> messages to different responders, but at the same time it can issue a
>> single message to a specific responder at a time.
>>
>> - As a PLDM requester, the BMC must be able to handle out of order
>> responses.
>>
>> - As a PLDM responder, the BMC may simultaneously respond to messages
>> from different requesters, but the spec doesn't mandate this. In other
>> words the responder could be single-threaded.
>>
>> - It should be possible to plug-in non-existent PLDM functions (these
>> maybe new/existing standard Types, or OEM Types) into the PLDM stack.
>>
>> ## Proposed Design
>>
>> The following are high level structural elements of the design:
>>
>> ### PLDM encode/decode libraries
>>
>> This library would take a PLDM message, decode it and spit out the
>> different fields of the message. Conversely, given a PLDM Type, command
>> code, and the command's data fields, it would make a PLDM message. The
>> thought is to design this library such that it can be used by BMC and
>> the host firmware stacks, because it's the encode/decode and protocol
>> piece (and not the handling of a message). I'd like to know if there's
>> enough motivation to have this as a common lib. That would mean
>> additional requirements such as having this as a C lib instead of C++,
>> because of the runtime constraints of host firmware stacks. If there's
>> not enough interest to have this as a common lib, this could just be
>> part of the provider libs (see below), and it could then be written in C++.
> 
> 
> Can you elaborate a bit on the pros and cons of having PLDM library as a common C lib vs them
> being provider libs only?

These two are exclusive of each other, meaning what can be common is the 
encoding and decoding alone. The provider libs would be platform 
specific. I think the main advantage of having the common piece is the 
BMC and every other host firmware stack needn't re-implement this part. 
So while we should strive for this, I guess some host firmware stack 
might not find it usable (even if it's in C) due to other constraints. 
These constraints might not be determinable exhaustively a priori, so 
the disadvantage is that I'm not sure if the common lib is worth the 
effort as opposed to the liberty of using something like modern C++ to 
code this.

>>
>> There would be one encode/decode lib per PLDM Type. So for e.g.
>> something like /usr/lib/pldm/libbase.so, /usr/lib/pldm/libfru.so, etc.
>>
>> ### PLDM provider libraries
>>
>> These libraries would implement the platform specific handling of
>> incoming PLDM requests (basically helping with the PLDM responder
>> implementation, see next bullet point), so for instance they would query
>> D-Bus objects (or even something like a JSON file) to fetch platform
>> specific information to respond to the PLDM message. They would link
>> with the encode/decode libs. Like the encode/decode libs, there would be
>> one per PLDM Type (for e.g /usr/lib/pldm/providers/libfru.so).
>>
>> These libraries would essentially be plug-ins. That lets someone add
>> functionality for new PLDM (standard as well as OEM) Types, and it also
>> lets them replace default handlers. The libraries would implement a
>> "register" API to plug-in handlers for specific PLDM messages. Something
>> like:
>>
>> template <typename Handler, typename... args>
>> auto register(uint8_t type, uint8_t command, Handler handler);
>>
>> This allows for providing a strongly-typed C++ handler registration
>> scheme. It would also be possible to validate the parameters passed to
>> the handler at compile time.
>>
>> ### Request/Response Model
>>
>> There are two approaches that I've described here, and they correlate to
>> the two options in Jeremy's MCTP design for how to notify on incoming
>> PLDM messages: in-process callbacks vs D-Bus signals.
>>
>> #### With in-process callbacks
>>
>> In this case, there would be a single PLDM (over MCTP) daemon that
>> implements both the PLDM responder and PLDM requester function. The
>> daemon would link with the encode/decode libs mentioned above, and the
>> MCTP lib.
> 
> In the case if we want to run PLDM over NCSI, do you envision having a separate
> NCSI daemon that also link with PLDM decode/encode lib? So in this case there'd
> be multiple stream of (separate) PLDM traffic.

That's one way. Having separate daemons (linking to shared PLDM 
libraries) per transport channel gives us greater flexibility at not too 
much additional cost, I think.

>>
>> The PLDM responder function would involve registering the PLDM provider
>> libs on startup. The PLDM responder implementation would sit in the
>> callback handler from the transport's rx. If it receives PLDM messages
>> of type Request, it will route them to an appropriate handler in a
>> provider lib, get the response back, and send back a PLDM response
>> message via the transport's tx API. If it receives messages of type
>> Response, it will put them on a "Response queue".
> 
> Do you see any needs for handler in the provider lib to communicate with
> other daemons?

Yes.

For example, PLDM sensor handler may have to query a separate
> sensor daemon (sensord) to get the sensor data before it can respond.
> 
> If the handler needs to communicate with other daemons/applications in the system,
> I think this part of the design would be very similar to the "BMC as PLDM requester" design
> you've specified below.
> 
> e.g.
> The response from sensord may not return right away, and the PLDM handler shouldn't
> block, in this case I think the handler for each PLDM type  would also need a "Request Queue"
> so it may queue up  incoming requests while it processes each request.
> 
> Also if each PLDM Type handler needs to communicate with multiple daemons, I'm thinking having
> a msg_in  queue (in addition to the Request queue above) so it may receive responses back
> from other daemons in the system, and store PLDM IID in meta-data when
> communicating with other daemons so the PLDM handler can map each messages in
> msg_in queue to a PLDM request in Request Queue.
> 
> In this case each PLDM handler would need multiple threads to handle these separate tasks.

All this sounds reasonable to me. Implementation-wise, we might have to 
carefully consider multi-threading as opposed to using a single thread 
with ASIO/event loop.

>>
>> I think designing the BMC as a PLDM requester is interesting. We haven't
>> had this with IPMI, because the BMC was typically an IPMI server. I
>> envision PLDM requester functions to be spread across multiple OpenBMC
>> applications (instead of a single big requester app) - based on the
>> responder they're talking and the high level function they implement.
>> For example, there could be an app that lets the BMC upgrade firmware
>> for other devices using PLDM - this would be a generic app in the sense
>> that the same set of commands might have to be run irrespective of the
>> device on the other side. There could also be an app that does fan
>> control on a remote device, based on sensors from that device and
>> algorithms specific to that device.
>>
>> The PLDM daemon would have to provide a D-Bus interface to send a PLDM
>> request message. This API would be used by apps wanting to send out PLDM
>> requests. If the message payload is too large, the interface could
>> accept an fd (containing the message), instead of an array of bytes. The
>> implementation of this would send the PLDM request message via the
>> transport's tx API, and then conditionally wait on the response queue to
>> have an entry that matches this request (the match is by instance id).
>> The conditional wait (or something equivalent) is required because the
>> app sending the PLDM message must block until getting a response back
>> from the remote PLDM device.
>>
>> With what's been described above, it's obvious that the responder and
>> requester functions need to be able to run concurrently (this is as per
>> the PLDM spec as well). The BMC can simultaneously act as a responder
>> and requester. Waiting on a rx from the transport layer shouldn't block
>> other BMC apps from sending PLDM messages. So this means the PLDM daemon
>> would have to be multi-threaded, or maybe we can instead achieve this
>> via an event loop.
> 
> Do you see both Requester and Responder spawning multiple threads?

As per the base specification, I understand that the responder and 
requester functions should not block each other out. The base spec says 
a requester terminus should wait for a response from the other end 
before sending a new command. The spec also says a responder may 
optionally be multi-threaded. So I guess the answer depends on whether 
we view the BMC as a single requester, or multiple virtual requesters. 
As a responder, the BMC must definitely be able to respond to different 
transport channels concurrently. I'm not sure yet if concurrency is 
required on the same transport channel.

> I can see them performing similar functionalities,
> 
> e.g. perhaps something like this below:
> 
> PLDM Requester
> - listens for other applications/daemons for PLDM requests, and generate and send PLDM
>     Requests to device (1 thread)
> - waits for device response,  look up original request sender via response IID and send
>     response back to applications/daemons (1 thread)
> 
> PLDM Responder
>    - listens for PLDM requests from device, decode request and add it to corresponding handler's Request queue (1 thread)
> - each handler:
> 	- checks its Request Queue, process request inline (if able to) and adds response to response queue,
>                     If request needs data from other application, send message to other application (1 thread)
>              - processes incoming messages from other applications and put them to Response queue (1 thread)
>              - process Response queue - send response back to device (1 thread)
> 
>> #### With D-Bus signals
>>
>> This lets us separate PLDM daemons from the MCTP daemon, and eliminates
>> the need to handle request and response messages concurrently in the
>> same daemon, at the cost of much more D-Bus traffic. The MCTP daemon
>> would emit D-Bus signals describing the type of the PLDM message
>> (request/response) and containing the message payload. Alternatively it
>> could pass the PLDM message over a D-Bus API that the PLDM daemons would
>> implement. The MCTP daemon would also implement a D-Bus API to send PLDM
>> messages, as with the previous approach.
>>
>> With this approach, I'd recommend two separate PLDM daemons - a
>> responder daemon and a requester daemon. The responder daemon reacts to
>> D-Bus signals corresponding to PLDM Request messages. It handles
>> incoming requests as before. The requester daemon would react to D-Bus
>> signals corresponding to PLDM response messages. It would implement the
>> instance id generation, and would also implement the response queue and
>> the conditional wait on that queue. It would also have to implement a
>> D-Bus API to let other PLDM-enabled OpenBMC apps send PLDM requests. The
>> implementation of that API would send the message to the MCTP daemon,
>> and then block on the response queue to get a response back.
> 
> Similar to previous "in-process callback" approach, the  Responder daemon may
> have to send D-Bus signals to other applications in order process a PLDM request?

I was thinking the responder would make D-Bus method calls.

> Is there a way for any daemons in the system to register a communication channel
> With PLDM handler?

That's a good question. We should design an API for this.

>> ### Multiple requesters and responders
>>
>> The PLDM spec does allow simultaneous connections between multiple
>> responders/requesters. For e.g. the BMC talking to a multi-host system
>> on two different physical channels. Instead of implementing this in one
>> MCTP/PLDM daemon, we could spawn one daemon per physical channel.
> 
> OK I see, so in this case a daemon monitor MCTP channel would have its own PLDM
> handler, and a daemon monitoring NCSI channel would spawn its PLDM handler,
> both streams of PLDM traffic occurs independently of each other and have its own
> series of instance IDs.
> 
>> ## Impacts
>>
>> Development would be required to implement the PLDM protocol, the
>> request/response model, and platform specific handling. Low level design
>> is required to implement the protocol specifics of each of the PLDM
>> Types. Such low level design is not included in this proposal.
>>
>> Design and development needs to involve potential host firmware
>> implementations.
>>
>> ## Testing
>>
>> Testing can be done without having to depend on the underlying transport
>> layer.
>>
>> The responder function can be tested by mocking a requester and the
>> transport layer: this would essentially test the protocol handling and
>> platform specific handling. The requester function can be tested by
>> mocking a responder: this would test the instance id handling and the
>> send/receive functions.
>>
>> APIs from the shared libraries can be tested via fuzzing.
> 
> Thanks!
> -Ben

Please do let me know if you have additional questions. I plan to 
incorporate your feedback, and I'll most likely post the next draft on 
Gerrit.

Thanks,
Deepak

RE: PLDM design proposal

[Ben Wei]

Hi Deepak,

Thanks for providing the detailed design and the background info. 
I just have some questions and comments below, 

> Hi All,
>
> I've put down some thoughts below on an initial PLDM design on OpenBMC. 
> The structure of the document is based on the OpenBMC design template. 
> Please review and let me know your feedback. Once we've had a discussion 
> here on the list, I can move this to Gerrit with some more details. I'd 
> say reading the MCTP proposal from Jeremy should be a precursor to 
> reading this.
>
> # PLDM Stack on OpenBMC
>
> Author: Deepak Kodihalli <dkodihal@linux.vnet.ibm.com> <dkodihal>
>
> ## Problem Description
>
> On OpenBMC, in-band IPMI is currently the primary industry-standard 
> means of communication between the BMC and the Host firmware. We've 
> started hitting some inherent limitations of IPMI on OpenPOWER servers: 
> a limited number of sensors, and a lack of a generic control mechanism 
> (sensors are a generic monitoring mechanism) are the major ones. There 
> is a need to improve upon the communication protocol, but at the same 
> time inventing a custom protocol is undesirable.
>
> This design aims to employ Platform Level Data Model (PLDM), a standard 
> application layer communication protocol defined by the DMTF. PLDM draws 
> inputs from IPMI, but it overcomes most of the latter's limitations. 
> PLDM is also designed to run on standard transport protocols, for e.g. 
> MCTP (also designed by the DMTF). MCTP provides for a common transport 
> layer over several physical channels, by defining hardware bindings. The 
> solution of PLDM over MCTP also helps overcome some of the limitations 
> of the hardware channels that IPMI uses.
>
> PLDM's purpose is to enable all sorts of "inside the box communication": 
> BMC - Host, BMC - BMC, BMC - Network Controller and BMC - Other (for 
> e.g. sensor) devices. This design doesn't preclude enablement of 
> communication channels not involving the BMC and the host.
>
> ## Background and References
>
> PLDM is designed to be an effective interface and data model that 
> provides efficient access to low-level platform inventory, monitoring, 
> control, event, and data/parameters transfer functions. For example, 
> temperature, voltage, or fan sensors can have a PLDM representation that 
> can be used to monitor and control the platform using a set of PLDM 
> messages. PLDM defines data representations and commands that abstract 
> the platform management hardware.
>
> As stated earlier, PLDM is designed for different flavors of "inside the 
> box" communication. PLDM groups commands under broader functions, and 
> defines separate specifications for each of these functions (also called 
> PLDM "Types"). The currently defined Types (and corresponding specs) are 
>: PLDM base (with associated IDs and states specs), BIOS, FRU, Platform 
> monitoring and control, Firmware Update and SMBIOS. All these 
> specifications are available at:
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.dmtf.org_standards_pmci&d=DwICAg&c=5VD0RTtNlTh3ycd41b3MUw&r=U35IaQ-7Tnwjs7q_Fwf_bQ&m=hfNgxW6BBJnW0LRRa3Hh2xnPH29lrZDGcvqooGTWVjc&s=qOY-dlAn__E9D7LWH6L16US1Sq8lsCZQX1zJv36BLN0&e=
>
> Some of the reasons PLDM sounds promising (some of these are advantages 
> over IPMI):
>
> - Common in-band communication protocol.
>
> - Already existing PLDM Type specifications that cover the most common 
> communication requirements. Up to 64 PLDM Types can be defined (the last 
> one is OEM). At the moment, 6 are defined. Each PLDM type can house up 
> to 256 PLDM commands.
>
> - PLDM sensors are 2 bytes in length.
>
> - PLDM introduces the concept of effecters - a control mechanism. Both 
> sensors and effecters are associated to entities (similar to IPMI, 
> entities cab be physical or logical), where sensors are a mechanism for 
> monitoring and effecters are a mechanism for control. Effecters can be 
> numeric or state based. PLDM defines commonly used entities and their 
> IDs, but there 8K slots available to define OEM entities.
> 
> - PLDM allows bidirectional communication, and sending asynchronous events.
>
> - A very active PLDM related working group in the DMTF.
>
> The plan is to run PLDM over MCTP. MCTP is defined in a spec of its own, 
> and a proposal on the MCTP design is in discussion already. There's 
> going to be an intermediate PLDM over MCTP binding layer, which lets us 
> send PLDM messages over MCTP. This is defined in a spec of its own, and 
> the design for this binding will be proposed separately.
>
> ## Requirements
>
> How different BMC/Host/other applications make use of PLDM messages is 
> outside the scope of this requirements doc. The requirements listed here 
> are related to the PLDM protocol stack and the request/response model:
>
> - Marshalling and unmarshalling of PLDM messages, defined in various 
> PLDM Type specs, must be implemented. This can of course be staged based 
> on the need of specific Types and functions. Since this is just encoding 
> and decoding PLDM messages, I believe there would be motivation to build 
> this into a library that could be shared between BMC, host and other 
> firmware stacks. The specifics of each PLDM Type (such as FRU table 
> structures, sensor PDR structures, etc) are implemented by this lib.
>
> - Mapping PLDM concepts to native OpenBMC concepts must be implemented. 
> For e.g.: mapping PLDM sensors to phosphor-hwmon hosted D-Bus objects, 
> mapping PLDM FRU data to D-Bus objects hosted by 
> phosphor-inventory-manager, etc. The mapping shouldn't be restrictive to 
> D-Bus alone (meaning it shouldn't be necessary to put objects on the Bus 
> just so serve PLDM requests, a problem that exists with 
> phosphor-host-ipmid today). Essentially these are platform specific PLDM 
> message handlers.
>
> - The BMC should be able to act as a PLDM responder as well as a PLDM 
> requester. As a PLDM responder, the BMC can monitor/control other 
> devices. As a PLDM responder, the BMC can react to PLDM messages 
> directed to it via requesters in the platform, for e.g, the Host.
>
> - As a PLDM requester, the BMC must be able to discover other PLDM 
> enabled components in the platform.
>
> - As a PLDM requester, the BMC must be able to send simultaneous 
> messages to different responders, but at the same time it can issue a 
> single message to a specific responder at a time.
>
> - As a PLDM requester, the BMC must be able to handle out of order 
> responses.
>
> - As a PLDM responder, the BMC may simultaneously respond to messages 
> from different requesters, but the spec doesn't mandate this. In other 
> words the responder could be single-threaded.
>
> - It should be possible to plug-in non-existent PLDM functions (these 
> maybe new/existing standard Types, or OEM Types) into the PLDM stack.
>
> ## Proposed Design
>
> The following are high level structural elements of the design:
>
> ### PLDM encode/decode libraries
>
> This library would take a PLDM message, decode it and spit out the 
> different fields of the message. Conversely, given a PLDM Type, command 
> code, and the command's data fields, it would make a PLDM message. The 
> thought is to design this library such that it can be used by BMC and 
> the host firmware stacks, because it's the encode/decode and protocol 
> piece (and not the handling of a message). I'd like to know if there's 
> enough motivation to have this as a common lib. That would mean 
> additional requirements such as having this as a C lib instead of C++, 
> because of the runtime constraints of host firmware stacks. If there's 
> not enough interest to have this as a common lib, this could just be 
> part of the provider libs (see below), and it could then be written in C++.


Can you elaborate a bit on the pros and cons of having PLDM library as a common C lib vs them
being provider libs only?


>
> There would be one encode/decode lib per PLDM Type. So for e.g. 
> something like /usr/lib/pldm/libbase.so, /usr/lib/pldm/libfru.so, etc.
>
> ### PLDM provider libraries
>
> These libraries would implement the platform specific handling of 
> incoming PLDM requests (basically helping with the PLDM responder 
> implementation, see next bullet point), so for instance they would query 
> D-Bus objects (or even something like a JSON file) to fetch platform 
> specific information to respond to the PLDM message. They would link 
> with the encode/decode libs. Like the encode/decode libs, there would be 
> one per PLDM Type (for e.g /usr/lib/pldm/providers/libfru.so).
>
> These libraries would essentially be plug-ins. That lets someone add 
> functionality for new PLDM (standard as well as OEM) Types, and it also 
> lets them replace default handlers. The libraries would implement a 
> "register" API to plug-in handlers for specific PLDM messages. Something 
> like:
>
> template <typename Handler, typename... args>
> auto register(uint8_t type, uint8_t command, Handler handler);
>
> This allows for providing a strongly-typed C++ handler registration 
> scheme. It would also be possible to validate the parameters passed to 
> the handler at compile time.
>
> ### Request/Response Model
>
> There are two approaches that I've described here, and they correlate to 
> the two options in Jeremy's MCTP design for how to notify on incoming 
> PLDM messages: in-process callbacks vs D-Bus signals.
>
> #### With in-process callbacks
>
> In this case, there would be a single PLDM (over MCTP) daemon that 
> implements both the PLDM responder and PLDM requester function. The 
> daemon would link with the encode/decode libs mentioned above, and the 
> MCTP lib.

In the case if we want to run PLDM over NCSI, do you envision having a separate 
NCSI daemon that also link with PLDM decode/encode lib? So in this case there'd
be multiple stream of (separate) PLDM traffic.

>
> The PLDM responder function would involve registering the PLDM provider 
> libs on startup. The PLDM responder implementation would sit in the 
> callback handler from the transport's rx. If it receives PLDM messages 
> of type Request, it will route them to an appropriate handler in a 
> provider lib, get the response back, and send back a PLDM response 
> message via the transport's tx API. If it receives messages of type 
> Response, it will put them on a "Response queue".

Do you see any needs for handler in the provider lib to communicate with
other daemons? For example, PLDM sensor handler may have to query a separate 
sensor daemon (sensord) to get the sensor data before it can respond. 

If the handler needs to communicate with other daemons/applications in the system,
I think this part of the design would be very similar to the "BMC as PLDM requester" design
you've specified below.

e.g. 
The response from sensord may not return right away, and the PLDM handler shouldn't 
block, in this case I think the handler for each PLDM type  would also need a "Request Queue" 
so it may queue up  incoming requests while it processes each request.

Also if each PLDM Type handler needs to communicate with multiple daemons, I'm thinking having
a msg_in  queue (in addition to the Request queue above) so it may receive responses back
from other daemons in the system, and store PLDM IID in meta-data when
communicating with other daemons so the PLDM handler can map each messages in 
msg_in queue to a PLDM request in Request Queue.

In this case each PLDM handler would need multiple threads to handle these separate tasks.

>
> I think designing the BMC as a PLDM requester is interesting. We haven't 
> had this with IPMI, because the BMC was typically an IPMI server. I 
> envision PLDM requester functions to be spread across multiple OpenBMC 
> applications (instead of a single big requester app) - based on the 
> responder they're talking and the high level function they implement. 
> For example, there could be an app that lets the BMC upgrade firmware 
> for other devices using PLDM - this would be a generic app in the sense 
> that the same set of commands might have to be run irrespective of the 
> device on the other side. There could also be an app that does fan 
> control on a remote device, based on sensors from that device and 
> algorithms specific to that device.
>
> The PLDM daemon would have to provide a D-Bus interface to send a PLDM 
> request message. This API would be used by apps wanting to send out PLDM 
> requests. If the message payload is too large, the interface could 
> accept an fd (containing the message), instead of an array of bytes. The 
> implementation of this would send the PLDM request message via the 
> transport's tx API, and then conditionally wait on the response queue to 
> have an entry that matches this request (the match is by instance id). 
> The conditional wait (or something equivalent) is required because the 
> app sending the PLDM message must block until getting a response back 
> from the remote PLDM device.
>
> With what's been described above, it's obvious that the responder and 
> requester functions need to be able to run concurrently (this is as per 
> the PLDM spec as well). The BMC can simultaneously act as a responder 
> and requester. Waiting on a rx from the transport layer shouldn't block 
> other BMC apps from sending PLDM messages. So this means the PLDM daemon 
> would have to be multi-threaded, or maybe we can instead achieve this 
> via an event loop.

Do you see both Requester and Responder spawning multiple threads?

I can see them performing similar functionalities, 

e.g. perhaps something like this below:

PLDM Requester 
- listens for other applications/daemons for PLDM requests, and generate and send PLDM 
   Requests to device (1 thread)
- waits for device response,  look up original request sender via response IID and send 
   response back to applications/daemons (1 thread)

PLDM Responder
  - listens for PLDM requests from device, decode request and add it to corresponding handler's Request queue (1 thread)
- each handler:  
	- checks its Request Queue, process request inline (if able to) and adds response to response queue, 
                   If request needs data from other application, send message to other application (1 thread)
            - processes incoming messages from other applications and put them to Response queue (1 thread)
            - process Response queue - send response back to device (1 thread)  

> #### With D-Bus signals
>
> This lets us separate PLDM daemons from the MCTP daemon, and eliminates 
> the need to handle request and response messages concurrently in the 
> same daemon, at the cost of much more D-Bus traffic. The MCTP daemon 
> would emit D-Bus signals describing the type of the PLDM message 
> (request/response) and containing the message payload. Alternatively it 
> could pass the PLDM message over a D-Bus API that the PLDM daemons would 
> implement. The MCTP daemon would also implement a D-Bus API to send PLDM 
> messages, as with the previous approach.
>
> With this approach, I'd recommend two separate PLDM daemons - a 
> responder daemon and a requester daemon. The responder daemon reacts to 
> D-Bus signals corresponding to PLDM Request messages. It handles 
> incoming requests as before. The requester daemon would react to D-Bus 
> signals corresponding to PLDM response messages. It would implement the 
> instance id generation, and would also implement the response queue and 
> the conditional wait on that queue. It would also have to implement a 
> D-Bus API to let other PLDM-enabled OpenBMC apps send PLDM requests. The 
> implementation of that API would send the message to the MCTP daemon, 
> and then block on the response queue to get a response back.

Similar to previous "in-process callback" approach, the  Responder daemon may
have to send D-Bus signals to other applications in order process a PLDM request?

Is there a way for any daemons in the system to register a communication channel
With PLDM handler?

> ### Multiple requesters and responders
>
> The PLDM spec does allow simultaneous connections between multiple 
> responders/requesters. For e.g. the BMC talking to a multi-host system 
> on two different physical channels. Instead of implementing this in one 
> MCTP/PLDM daemon, we could spawn one daemon per physical channel.

OK I see, so in this case a daemon monitor MCTP channel would have its own PLDM
handler, and a daemon monitoring NCSI channel would spawn its PLDM handler,
both streams of PLDM traffic occurs independently of each other and have its own 
series of instance IDs.

> ## Impacts
>
> Development would be required to implement the PLDM protocol, the 
> request/response model, and platform specific handling. Low level design 
> is required to implement the protocol specifics of each of the PLDM 
> Types. Such low level design is not included in this proposal.
>
> Design and development needs to involve potential host firmware
> implementations.
>
> ## Testing
>
> Testing can be done without having to depend on the underlying transport 
> layer.
>
> The responder function can be tested by mocking a requester and the 
> transport layer: this would essentially test the protocol handling and 
> platform specific handling. The requester function can be tested by 
> mocking a responder: this would test the instance id handling and the 
> send/receive functions.
>
> APIs from the shared libraries can be tested via fuzzing.

Thanks!
-Ben

Re: PLDM design proposal

[Ben Wei]

Hi Deepak, 

On 19/12/18 5:41 AM, Ben Wei wrote:
>>>>> Hi All,
>>>>>
>>>>> I've put down some thoughts below on an initial PLDM design on OpenBMC.
>>>>> The structure of the document is based on the OpenBMC design template.
>>>>> Please review and let me know your feedback. Once we've had a 
>>>>> discussion here on the list, I can move this to Gerrit with some 
>>>>> more details. I'd say reading the MCTP proposal from Jeremy should 
>>>>> be a precursor to reading this.
>> 
>>> Hi Deepak,
>>> 
>>> Do you see any issues with running PLDM over NCSI/RBT?
>>> If the NCSI daemon implements the same in-process callbacks as the 
>>> MCTP daemon, (or if it supports the same D-Bus interface which takes 
>>> PLDM payload and encapsulate it as NCSI commands)
>
>Nothing jumps out as a problem with this.
>
>>> Also do you have plans on which PLDM functionalities to implement first?
>>> I'm looking at creating a prototype user library for PLDM firmware update would love to collaborate.
> 
> That sounds great! PLDM platform monitoring and BIOS are likely to be first on our list in terms of the order of implementation.  I did see some code being dropped at facebook/openbmc, related to PLDM firmware upgrade. Is that a prototype 
> and/or do you eventually plan to drop that openbmc as well? I'd love to hear feedback from you on the high level design that I sent. I'm planning to push that to Gerrit, so you could review there as well.

Great,  I'm currently prototyping PDLM firmware update functionality on one of facebook's platforms.  I plan to port that to openbmc once my prototyping is done.
At the moment it's in a shared library libpldm that parses and generate some base PLDM command parsing but mainly type 5 commands for PLDM firmware update. 
It's using NCSI as transporting layer for now but I can port it to MCTP as well.  I will review the high level design you sent earlier and comment. 

Thanks!
-Ben

Re: PLDM design proposal

[Deepak Kodihalli]

On 19/12/18 5:41 AM, Ben Wei wrote:
>>> Hi All,
>>>
>>> I've put down some thoughts below on an initial PLDM design on OpenBMC.
>>> Thie structure of the document is based on the OpenBMC design template.
>>> Please review and let me know your feedback. Once we've had a discussion
>>> here on the list, I can move this to Gerrit with some more details. I'd
>>> say reading the MCTP proposal from Jeremy should be a precursor to
>>> reading this.
> 
> Hi Deepak,
> 
> Do you see any issues with running PLDM over NCSI/RBT?
> If the NCSI daemon implements the same in-process callbacks as the MCTP daemon,
> (or if it supports the same D-Bus interface which takes PLDM payload and encapsulate it as NCSI commands)

Nothing jumps out as a problem with this.

> Also do you have plans on which PLDM functionalities to implement first?
> I'm looking at creating a prototype user library for PLDM firmware update would love to collaborate.

That sounds great! PLDM platform monitoring and BIOS are likely to be 
first on our list in terms of the order of implementation.  I did see 
some code being dropped at facebook/openbmc, related to PLDM firmware 
upgrade. Is that a prototype and/or do you eventually plan to drop that 
openbmc as well? I'd love to hear feedback from you on the high level 
design that I sent. I'm planning to push that to Gerrit, so you could 
review there as well.

>   Thanks!
> -Ben
> 

PLDM design proposal

[Ben Wei]

>> Hi All,
>>
>> I've put down some thoughts below on an initial PLDM design on OpenBMC. 
>> Thie structure of the document is based on the OpenBMC design template. 
>> Please review and let me know your feedback. Once we've had a discussion 
>> here on the list, I can move this to Gerrit with some more details. I'd 
>> say reading the MCTP proposal from Jeremy should be a precursor to 
>> reading this.

Hi Deepak, 

Do you see any issues with running PLDM over NCSI/RBT?  
If the NCSI daemon implements the same in-process callbacks as the MCTP daemon, 
(or if it supports the same D-Bus interface which takes PLDM payload and encapsulate it as NCSI commands)

Also do you have plans on which PLDM functionalities to implement first?
I'm looking at creating a prototype user library for PLDM firmware update would love to collaborate.

 Thanks!
-Ben