[PATCH v2] usb: ehci-hcd: Add IAA handshake for removing async QH

[Marek Vasut]

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:
> 1. Build the UEFI SCT from https://github.com/tianocore/edk2-test
> 2. Build the EDK2 UEFI Shell from https://github.com/tianocore/edk2
> 3. Copy SCT files and Shell.efi to USB disk FAT partition
> 4. Load the Shell.efi from USB FAT, and run bootefi to execute it
> 5. After booting into Shell, enter the SCT directory and run "sct -a"
>     to execute all tests.
> 6. 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.