Hi Felipe, It's dangerous to use Update Transfer when the DWC3_TRB_CTRL_LST bit might be set in one of the TRBs. The reason is, there is a window between checking that the transfer has not completed yet and issuing the Update Transfer command. If the hardware happens to complete the transfer and see the DWC3_TRB_CTRL_LST bit set within that window, then the Update Transfer command will not work, and a Start Transfer command will be required instead.
So it's only safe to use Update Transfer if (a) you have a circular TRB chain where no TRB has the _LST bit set, or (b) you have a deep TRB chain, and the hardware is far enough away from the end that you can be sure it can't reach the TRB with the _LST bit set before you issue the Update Transfer command. Paul Z, Retired but still reading the Linux lists from time to time -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
