This option is used to start up the hw_server with the ability to enable ir lengths greater than 64 bits. The default value for this setting is 64. You can increase this value for devices in the JTAG chains whose ir length are wider (for example 93). Note that increasing this number will slow the device discovery process, which in turn can slow cable access. Therefore, you should only increase this value for systems with long ir lengths and device counts.
This is how you specify the option at hw_server start-up:
hw_server -e "set max-ir-length 93"