FW burn issue solution design

Signed-off-by: liora <liora@nvidia.com>

doc/fw_burn_init_issue/solution_design.md

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+# FW Burn Init Issue
+# Overview
+- We have an issue in init flow when FW burn takes place.
+- We can see that SWSS Orchagent tries to configure Syncd while FW burn takes place.
+- Since the flow is valid the decision that was taken is to increase timeout for Orchagent calls.
+![fw_burn_init_issue](issue_description.svg "Figure 1: BFD in SONiC Architecture")
+
+# High-Level Design
+- We set the timeout for SAI Redis calls in Orchagent init flow.
+- Timeout value determined by system type.
+- We have 2 system types, with and without Gearbox.
+- In systems without Gearbox, FW burn takes ~2 min -> set timeout to 150 seconds
+- In systems with Gearbox, FW burn takes ~7 min -> set timeout to 480 seconds
+- See below table with time measurements
+
+|Operation|SPC1|SPC2|SPC3|SPC2 with Gearbox
+|--|--|--|--|--|
+|MST start|2s|2s|2s|2s
+|FW burn|1m55s|1m27s|1m32s|1m35s
+|SXD start|3s|12s|42s|5m26s
+|Whole process|2m|1m41s|2m16s|7m3s
+
+# API
+- This API allows us to set the timeout for SAI Redis API calls.
+- Identifier: SAI_REDIS_SWITCH_ATTR_GET_RESPONSE_TIMEOUT_MS
+- Value: determined by system type.