On 3/9/21 4:26 AM, Ye Li wrote:
According to EHCI spec, software needs to do handshake with HC for safely removing QH from async list. This handshake is implemented by setting IAAD (Interrupt on Async Advance Doorbell) bit in USB_USBCMD register and poll the IAA (Interrupt on Async Advance bit) in the USB_USBSTS to ensure the HC has released all on-chip state that may potentially reference one of the data structures just removed.
Current codes only check active status of the last QTD, but this can't ensure the QH is released from HC. We can meet unrecoverable "EHCI timed out on TD" errors when running UEFI SCT tests on USB disk. The USB_ASYNCLISTADDR register is changed to a invalid address when the issue happens. It is fixed after adding the IAA handshake.
Steps to reproduce the issue:
- Build the UEFI SCT from https://github.com/tianocore/edk2-test
- Build the EDK2 UEFI Shell from https://github.com/tianocore/edk2
- Copy SCT files and Shell.efi to USB disk FAT partition
- Load the Shell.efi from USB FAT, and run bootefi to execute it
- After booting into Shell, enter the SCT directory and run "sct -a" to execute all tests.
- Tests run about 1 hour and stop with many EHCI timeout errors like EHCI timed out on TD - token=0x801f8c80
Applied to usb/next, thanks.