Re: OHCI hangs after failing to free resources

On Sat, 28 Apr 2007, Mike Nuss wrote:

> > This has nothing to do with polling or bInterval.  The host controller is
> > supposed to generate an interrupt at the start of each frame (once per
> > millisecond) provided the appropriate IRQ-enable flag is set.  INTR_SF ==
> > INTeRrupt at Start of Frame.  These are the interrupts which apparently
> > don't occur -- although your debugging may uncover other problems.
> 
> So it seems like if the host controller were not generating INTR_SF at
> all, the host wouldn't get data from any of the attached devices.

No, I don't think that's right.  The data transfers work more or less
independently from the Start Of Frame interrupts, because each time a
transfer completes the host controller generates another IRQ -- or at
least, it's supposed to.  The SOF interrupts are needed pretty much only
for unlinking URBs, which is why you see problems in the endpoint_disable
routine (since part of disabling an endpoint is to unlink any outstanding 
URBs queued for that endpoint).

> The
> behavior I'm seeing is that one or more devices' read queues will 'lock
> up' (and the problem doesn't become critical until the device is removed
> and hcd_endpoint_disable is called) but the rest keep working.

It sounds like there's something seriously wrong with the host controller
hardware, and I don't mean just the SOF stuff.  When the problem occurs
you might be able to get some useful information from the OHCI debugging
files in

	/sys/class/usb_host/usb_hostN/

where N is the bus number of the failing controller.  (Note: these files
are present only if you set CONFIG_USB_DEBUG when building the kernel.)

Alan Stern


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