CRITICALITY

Low

DESCRIPTION

USB xHCI Stop Endpoint feature can, in addition to other scenarios, be used to recover from a situation where a particular endpoint of the attached device has become unresponsive due to various reasons. By stopping the endpoint, the xHCI host would normally stop all ongoing communication with the said endpoint. Other endpoints are not affected.

Due to the bug, in the following scenario, the Stop Endpoint will not function correctly:

• USB Controller connected to a Highspeed hub through zero or more hubs.
• FullSpeed device connected to any of the above hubs.
• Assume the USB Controller has already enumerated the Hub.
• USB Controller now starts to enumerate the FullSpeed device. In the Address Device step, BSR is set to 1.
• Next it performs GetDescriptor (device not addressed yet since BSR=1).
• Suppose that the FullSpeed device has is faulty and does not respond to the GetDescriptor Setup stage.
• The GetDescriptor is now stuck in CSPLIT-SETUP-NYET.
• At this point the application intends to recover from this error.

The Stop Endpoint when issued at this point never completes and the xHCI Controller will continuous send the CSPLIT-SETUP command since it never receives an ACK. In addition an attempt to abort the command using the CA bit in CRCR register also does not succeed.

WORKAROUND

Option 1: In the Address Device command set BSR=0 so that SET_ADDRESS command is actually executed before GetDescriptor.

Option 2: Instead of Stop Endpoint, perform the Disable Slot command. The difference from Stop Endpoint is that this command shall stop all endpoints and interfaces associated with the device.

REVISIONS IMPACTED

SR 2.0, 1.1

TDA2x: 2.0, 1.1, 1.0

DRA75x, DRA74x: 2.0, 1.1, 1.0

AM572x: 2.0, 1.1