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List:       linux-usb-devel
Subject:    Re: [linux-usb-devel] 2.4.0-test9-pre7 -- Weirdness in enumerating
From:       David Brownell <david-b () pacbell ! net>
Date:       2000-09-29 15:07:15
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Good find Roman -- that sounds like it's the explanation.

> >         usb-ohci.c: bogus NDP=66 for OHCI usb-00:07.4
> >         usb-ohci.c: rereads as NDP=4
> >         usb-ohci.c: bogus NDP=91 for OHCI usb-00:07.4
> >         usb-ohci.c: rereads as NDP=4
> >         usb-ohci.c: bogus NDP=128 for OHCI usb-00:07.4
> >         usb-ohci.c: rereads as NDP=4
> 
> This could be a 'feature' of the AMD 756 D2:

D2 being a chip revision; D4 (current rev since at least May)
allegedly fixes it.

Workarounds noted include applying a BIOS update or a new OHCI
driver from Microsoft ... :-)

Before we put the diagnostic ("bogus NDP...") in, we used
to see Oopsing.  Do we have any bad symptoms associated with
this failure any more, other than the diagnostic?

- Dave


> From 
> AMD-756" Peripheral Bus Controller Revision Guide
> (http://www.amd.com/products/cpg/athlon/techdocs/pdf/22591.pdf)
> chapter 2 Product Errata/ point 4 USB Controller:
> ...
> When the AMD-756 peripheral bus controller is performing USB-initiated
> PCI master cycles and a USB device is initialized, it may not be
> detected correctly. During this time, data corruption occurs in USB
> status registers located at offset locations 34h and above. This
> behavior only exists for low-speed devices. This behavior is seen in the
> following two cases:   
> Slow-speed devices are occasionally not detected at boot time.   
> Slow-speed devices are occasionally not detected when hot plugged.
> ...
> 
> The NDP value is from one of the status registers above 34h ...




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