uhci question

I am seeing in struct uhci_hcd,there is a struct uhci_td *term_td, and
hence in uhci_start, there are such lines:

    638         /* This dummy TD is to work around a bug in Intel PIIX
controllers */
    639         uhci_fill_td(uhci->term_td, 0, uhci_explen(0) |
    640                         (0x7f << TD_TOKEN_DEVADDR_SHIFT) |
USB_PID_IN, 0);
    641         uhci->term_td->link = UHCI_PTR_TERM;
    642         uhci->skel_async_qh->element = uhci->skel_term_qh->element =
    643                         LINK_TO_TD(uhci->term_td);

I wonder what bug it is?Where can I find any description about this
bug.And how term_td can be a work around for that bug?

Regards
Jason

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