*IT WORKS* Re: CardBus USB 2.0 Controller (NEC uPD)

[Anthony Naggs]

In article <200306112244.10466.craig at xfoil.gank.org>, Craig Boston
<craig at xfoil.gank.org> writes
>Believe it or not, after futzing with the debugger for hours, reading the OHCI 
>spec, and trying to figure out why writing to the control registers works 
>exactly as it should but the card seems to ignore the ED list, I decided to 
>try something completely crazy and put the line
>
>pci_enable_busmaster(self);
>
>near the top of ohci_attach() in ohci_pci.c
>
>...and it worked!  I believe my first words upon seeing "ums0: <blah blah>" 
>were "You have GOT to be kidding me."

Great news.

>I'm attaching a (trivial) patch for the lazy :)  Be advised, this is far from 
>a general solution as it probably breaks some (many?) PCI-based controllers 
>that don't support bus mastering.

Sorry, I don't understand this comment.  All OHCI, UHCI & EHCI USB
controllers need PCI bus mastering in order to read & update their
various lists of pending & completed transfers.

Without bus mastering the system CPU has to do all this stuff in an
interrupt handler.  This can be quite a heavy cpu load, and is not
attractive on a PC.  (I've outlined this before, on hackers at .  E.g. the
ScanLogic SL811 needs an interrupt for every packet transfer, and
Philips PHCI devices [e.g. ISP1160] needs a whole frame's worth of data
to read & written every ms.)


Cheers,
Tony