For the Connection of Classic Bluetooth, there is a Link_Policy_Settings, which is one of the HCI configuration parameters.
The Link_Policy_Settings parameter determines the behavior of the local link manager (Link Manager) when it receives a request from the remote link manager, and is also used to decide to change the role (role) or enter Hold or Sniff mode. The local link manager will automatically accept or reject such requests from the remote device, and may even make the request automatically, depending on the value of the Link_Policy_Settings parameter of the corresponding Connection_Handle. When the value of the Link_Policy_Settings parameter for a Connection_Handle is changed, the new value will only be used for requests from remote devices or the local Link Manager itself after the command has completed. By enabling each mode individually, the host can choose to support any combination of modes of operation required. Multiple Link Manager policies can be specified for the Link_Policy_Settings parameter by bitwise ORing the different activity types.
Note: Regardless of the value of the Link_Policy_Settings parameter, the remote device can force the local BR/EDR controller to enter Hold mode (regardless of whether the local device is a Central device or a Peripheral peripheral device). However, it can only be forced into Hold mode after the connection has been put into Hold mode by LMP request (Link_Policy_Settings determines whether to accept or reject requests from remote devices). After this, the Hold mode can be enforced as long as the connection continues, regardless of the Hold mode setting in the Link_Policy_Settings parameter.
Note: If the implementation in the remote device is a "polite" implementation, it will not force the other device into Hold mode via LMP PDUs, so Link_Policy_Settings will always be followed.
| Bit Number |
Parameter Description |
| 0 |
Enable Role switch. |
| 1 |
Enable Hold mode. |
| 2 |
Enable Sniff mode. |
| All other bits |
Reserved for future use. |
reference:
1. Bluetooth core spec v5.3
Vol 4: Host Controller Interface -> Part E: Host Controller Interface Functional Specification -> 6 HCI configuration parameters-> 6.18 Link Policy Settings