CRITICALITY

High

DESCRIPTION

If there is ongoing activity on the EMIF interface via the DMM path, any reconfiguration of EMIF_FW firewall instance can result in a system hang. This applies only to the EMIF_FW firewall instance. All other firewall instances can be safely re-configured at run-time using the sequence mentioned in TRM.

To reconfigure the firewall configuration at run-time, following sequence is to be followed:

1. Set the REGUPDATE_CONTROL[0] BUSY_REQ bit to 0x1 to ensure that no transaction can reach the slave NIU (suspend).
2. Update the firewall registers as required.
3. Set the REGUPDATE_CONTROL[0] BUSY_REQ bit to 0x0 to resume the transactions.

In case of EMIF_FW firewall instance, the transactions to the slave (EMIF) are not blocked correctly in step 1 mentioned above. Initiator remains unaware that EMIF is not accepting commands and waits indefinitely for a response resulting in a system hang.

WORKAROUND

EMIF_FW firewall instance should not be reconfigured when there is on-going activity on the EMIF interface.

Following choices can be made based on practical constraints in the system.

1. All firewall configurations are done one-time during the initial boot-up phase where EMIF transactions can be easily guaranteed to be not active. This will typically be done by a secondary boot loader or any other initialization software.
2. Using inter-processor communication between all the cores in the system, ensure that there is no activity on the EMIF interface. At this point, firewall can be reconfigured safely.
3. For some use-cases, to achieve same effect as changing firewall configuration at run-time, user can use a combination of DMM/MMU/Firewalls. In this case, firewall configuration is done only once during boot. Access permissions are controlled using aliased memory map created using DMM and controlling access to this aliased memory map using MMU.

REVISIONS IMPACTED

SR 2.0, 1.1, 1.0

TDA2x: 2.0, 1.1, 1.0

DRA75x, DRA74x: 2.0, 1.1, 1.0

AM572x: 2.0, 1.1