Re: EHCI host controller failing to do a QTD overlay

On Monday 02 July 2007, Leyden, Mark wrote:
> Hi,
> 
> I'm having problems with an NEC EHCI host controller on a Linux based
> embedded system. We're currently using version 2.4.32 of the kernel but
> have included the USB changes made to the 2.4.34 kernel.

So I take it you can't try to reproduce this with 2.6.current?

The Linux 2.4 EHCI code is quite ancient, and has various bugs
that have been fixed in current kernels.  I can't even remember
the last time a bugfix went into that code.


> From the traces we have observed, it would appear that the host
> controller is failing to overlay the QTD into the respective QH's
> overlay area. 

There were a number of finickey behaviors in that area in the
older EHCI code.  You might look at the qh_completions() logic
and the code which adds TDs to a QH, comparing to 2.6.current;
there are various little dodgey races when reading and writing
the live TD lists, and it's very possible your embedded system
has timings that create trouble...

I recall there are some cases where various EHCI 0.95 implementations
had surprising behavior.  Usually it was at the level of overlaying
something that shouldn't have been overlaid, but there were a few
other oddities too.

- Dave

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