HLD for 'Have a deterministic approach in SONiC for Interface Link bring-up sequence'

doc/sfp-cmis/Interface-Link-bring-up-sequence.md

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+# Feature Name
+Deterministic Approach for Interface Link bring-up sequence
+
+# High Level Design Document
+#### Rev 0.7
+
+# Table of Contents
+  * [List of Tables](#list-of-tables)
+  * [Revision](#revision)
+  * [About This Manual](#about-this-manual)
+  * [Abbreviation](#abbreviation)
+  * [References](#references)
+  * [Problem Definition](#problem-definition)
+  * [Background](#background)
+  * [Objective](#objective)
+  * [Plan](#plan)
+  * [Pre-requisite](#pre-requisite)
+  * [Breakout handling](#breakout-handling)
+  * [Proposed Work-Flows](#proposed-work-flows)
+
+# List of Tables
+  * [Table 1: Definitions](#table-1-definitions)
+  * [Table 2: References](#table-2-references)
+
+# Revision
+| Rev |     Date    |       Author                       | Change Description                |
+|:---:|:-----------:|:----------------------------------:|-----------------------------------|
+| 0.1 | 08/16/2021  | Shyam Kumar                        | Initial version                       
+| 0.2 | 12/13/2021  | Shyam Kumar,  Jaganathan Anbalagan | Added uses-cases, workflows  
+| 0.3 | 01/19/2022  | Shyam Kumar,  Jaganathan Anbalagan | Addressed review-comments    
+| 0.4 | 01/26/2022  | Shyam Kumar,  Jaganathan Anbalagan | Addressed further review-comments 
+| 0.5 | 01/28/2022  | Shyam Kumar,  Jaganathan Anbalagan | Addressed further review-comments
+| 0.6 | 02/02/2022  | Shyam Kumar                        | Added feature-enablement workflow 
+| 0.7 | 02/02/2022  | Jaganathan Anbalagan               | Added Breakout Handling 
+
+
+# About this Manual
+This is a high-level design document describing the need to have determinstic approach for
+Interface link bring-up sequence and workflows for use-cases around it 
+
+# Abbreviation
+
+# Table 1: Definitions
+| **Term**       | **Definition**                                   |
+| -------------- | ------------------------------------------------ |
+| pmon           | Platform Monitoring Service                      |
+| xcvr           | Transceiver                                      |
+| xcvrd          | Transceiver Daemon                               |
+| CMIS           | Common Management Interface Specification        |
+| gbsyncd        | Gearbox (External PHY) docker container          |
+| DPInit         | Data-Path Initialization                         |
+| QSFP-DD        | QSFP-Double Density (i.e. 400G) optical module   |
+
+# References
+
+# Table 2 References
+
+| **Document**                                            | **Location**  |
+|---------------------------------------------------------|---------------|
+| CMIS v4 | [QSFP-DD-CMIS-rev4p0.pdf](http://www.qsfp-dd.com/wp-content/uploads/2019/05/QSFP-DD-CMIS-rev4p0.pdf) | 
+| CMIS v5 | [CMIS5p0.pdf](http://www.qsfp-dd.com/wp-content/uploads/2021/05/CMIS5p0.pdf) |
+
+
+# Problem Definition
+
+1.	Presently in SONiC, there is no synchronization between Datapath Init operation of CMIS complaint optical module and enabling ASIC (NPU/PHY) Tx which may cause link instability during administrative interface enable “config interface startup Ethernet” configuration and bootup scenarios. 
+
+    For CMIS-compliant active (optical) modules, the Host (NPU/PHY) needs to provide a valid high-speed Tx input signal at the required signaling rate and encoding type prior to causing a DPSM to exit from DPDeactivated state and to move to DP Init transient state.
+
+    Fundamentally it means - have a deterministic approach to bring-up the interface.
+
+    Also, this problem is mentioned ‘as outside-the-scope’ of ‘CMIS Application Initialization’ high-level design document
+      **(https://github.com/ds952811/SONiC/blob/0e4516d7bf707a36127438c7f2fa9cc2b504298e/doc/sfp-cmis/cmis-init.md#outside-the-scope)**
+
+2.  During administrative interface disable “config interface shutdown Ethernet”, only the ASIC(NPU) Tx is disabled and not the opticcal module Tx/laser. 
+      This will lead to power wastage and un-necessary fan power consumption to keep the module temperature in operating range 
+
+# Background
+
+  Per the ‘CMIS spec’,  ‘validation, diagnostics’ done by HW team' and 'agreement with vendors', 
+  need to follow following bring-up seq to enable port/interface with CMIS compliant optical modules in LC/chassis:
+
+    a) Enable port on NPU (bring-up port, serdes on the NPU ; enable signals) : syncd
+    b) Enable port on PHY (bring-up port, serdes on the PHY ; enable signals) : gbsyncd
+       - Wait for signal to stabilize on PHY   
+    c) Enable optical module (data path initializatio, turn laser on/ enable tx) : xcvrd
+
+  In boards not having PHY, #b) not needed but #a) and #c) sequence to be followed.
+
+  ## Clause from CMIS4.0 spec
+
+     Excerpt from CMIS4.0 spec providing detailed reasoning for the above-mentioned bring-up sequence
+
+  ![61f5b485-cf3b-4ca8-beac-9102b6feabfe](https://user-images.githubusercontent.com/69485234/147173702-f124fc9d-ef27-4816-b1a1-b4a44a5833a7.PNG)
+
+
+  ## Clause from CMIS5.0 spec
+
+     Excerpt from CMIS5.0 spec providing detailed reasoning for the above-mentioned bring-up sequence
+
+  ![96a35dc5-618f-418c-9593-5639a90f1b28](https://user-images.githubusercontent.com/69485234/147173164-5ad0123c-479a-4774-b3ee-12a81fdd7d7e.PNG)
+
+
+# Objective
+
+Have a determistic approach for Interface link bring-up sequence for all interfaces types i.e. below sequence to be followed:
+  1. Initialize and enable NPU Tx and Rx path
+  2. For system with 'External' PHY: Initialize and enable PHY Tx and Rx on both line and host sides; ensure host side link is up 
+  3. Then only perform optics data path initialization/activation/Tx enable (for CMIS complaint optical modules) and Tx enable (for SFF complaint optical modules)
+
+# Plan
+
+Plan is to follow this high-level work-flow sequence to accomplish the Objective:
+- xcvrd to subscribe to a new field “host_tx_ready” in port table state-DB
+- Orchagent will set the “host_tx_ready” to true/false based on the SET_ADMIN_STATE attribute return status from syncd/gbsyncd. (As part of SET_ADMIN_STATE attribute enable, the NPU Tx is enabled)
+- xcvrd process the “host_tx_ready” value change event and do optics datapath init / de-init using CMIS API
+- Per the discussion and agreement in sonic-chassis workgroup and OCP community, plan is to follow this proposal for all the known interfaces types- 400G/100G/40G/25G/10G. Reason being: 
+  - CMIS complaint optical modules:-
+      All CMIS complaint optical modules will follow this approach as recommended in the CMIS spec.
+  - SFF complaint optical modules:- 
+    - deterministic approach to bring the interface will eliminate any link stability issue which will be difficult to chase in the production network
+      e.g. If there is a PHY device in between, and this 'deterministic approach' is not followed, PHY may adapt to a bad signal or interface flaps may occur when the optics tx/rx  enabled during PHY initialization. 
+    - there is a possibility of interface link flaps with non-quiescent optical modules <QSFP+/SFP28/SFP+> if this 'deterministic approach' is not followed
+    - It helps bring down the optical module laser when interface is adminstiratively shutdown. Per the workflow here, this is acheived by xcvrd listening to host_tx_ready field from PORT_TABLE of STATE_DB. Turning the laser off would reduce the power consumption and avoid any lab hazard
+    - Additionally provides uniform workflow (from SONiC NOS) across all interface types with or without module presence. 
+  - This synchronization will also benefit SFP+ optical modules as they are "plug N play" and may not have quiescent functionality. (xcvrd can use the optional 'soft tx disable' ctrl reg to disable the tx)
+
+# Pre-requisite
+
+As mentioned above in 'Background' and 'Plan' sections, need to follow specified bring-up sequence.
+Work flows are designed considering SONiC NOS operating in sync mode.
+
+In case SONiC NOS operates in async mode, then expected behavior is - the return status of the set ADMIN_STATE attribute update in ASIC-DB (syncd/GBsyncd) will be treated to set the host_tx_ready in Orchagent.
+
+# Breakout Handling
+  - The new 'host_tx_ready' field of Port table in state-DB is created for every interface <regular/breakout interface>.
+  - Xcvrd processes the 'host_tx_ready' change event and is responsible to disable Tx/laser for all optical lanes or respective optical lane that belongs to the interface in case of breakout.
+  - Currently the logical mapping between the interface and optical lane is not present in xcvrd. Creating this logical mapping in xcvrd will address breakout interface handling.
+
+# Proposed Work-Flows
+
+Please refer to the  flow/sequence diagrams which covers the following required use-cases
+  - Enabling this feature 
+  - Transceiver initialization
+  - admin enable configurations 
+  - admin disable configurations
+  - No transceiver present
+
+# Feature enablement
+  This feature (optics Interface Link bring-up sequence) would be enabled on per platform basis.
+  There could be cases where vendor(s)/platform(s) may take time to shift from existing codebase to the model (work-flows) described in this document.
+  In order to avoid any breakage and ensure gradual migration of different platforms/vendors to this model, there would be new field (flag) in xcvrd to enable/disable this feature. 
+  When xcvrd spawns on LC/board, it would invoke platform plugin to check with the platform (hwsku) whether this feature is yet supported on underlying platform (board/LC) or not
+
+  Workflow :
+  ![Enabling 'Interface link bring-up sequence' feature(3)](https://user-images.githubusercontent.com/69485234/152266723-050377ce-d4de-4c67-a405-5acc66474d46.png)
+
+
+# Transceiver Initialization 
+  (at platform bootstrap layer)
+
+![LC boot-up sequence - optics INIT (platform bootstrap)](https://user-images.githubusercontent.com/69485234/152261613-e20dcda9-2adc-42aa-a1f1-4b8a47dd32af.png)
+
+# Applying 'interface admin startup' configuration
+
+![LC boot-up sequence - 'admin enable' Config gets applied](https://user-images.githubusercontent.com/69485234/147166867-56f3e82d-1b1c-4b7a-a867-5470ee6050e7.png)
+
+
+# Applying 'interface admin shutdown' configuration
+
+![LC boot-up sequence - 'admin disable' Config gets applied](https://user-images.githubusercontent.com/69485234/147166884-92c9af48-2d64-4e67-8933-f80531d821b4.png)
+
+# No transceiver present
+if transceiver is not present:
+ - All the workflows mentioned above will reamin same ( or get exercised) till host_tx_ready field update
+ - xcvrd will not perform any action on receiving host_tx_ready field update 
+
+
+# Out of Scope 
+Following items are not in the scope of this document. They would be taken up separately
+1. xcvrd restart 
+   - If the xcvrd goes for restart, then all the DB events will be replayed. 
+     Here the Datapath init/activate for CMIS compliant optical modules, tx-disable register set (for SFF complaint optical modules), will be a no-op if the optics is already in that state 
+2. syncd/gbsyncd/swss docker container restart
+   - Cleanup scenario - Check if the host_tx_ready field in STATE-DB need to be updated to “False” for any use-case, either in going down or coming up path 
+   - Discuss further on the possible use-cases
+3. CMIS API feature is not part of this design and the APIs will be used in this design. For CMIS HLD, Please refer to:
+   https://github.com/Azure/SONiC/blob/9d480087243fd1158e785e3c2f4d35b73c6d1317/doc/sfp-cmis/cmis-init.md
+4. Error handling of SAI attributes
+   a) At present, If there is a set attribute failure, orch agent will exit. 
+      Refer the error handling API : https://github.com/Azure/sonic-swss/blob/master/orchagent/orch.cpp#L885
+   b) Error handling for SET_ADMIN_STATUS attribute will be added in future.
+   c) A propabale way to handle the failure is to set a error handling attribute to respective container syncd/GBsyncd with attribute that is failed. 
+      The platform layer knows the error better and it will try to recover.
+