linux-kernel - Re: OHCI root_port_reset() deadly loop...

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Message-Id: <20071008.201653.43030513.davem@davemloft.net>
Date:	Mon, 08 Oct 2007 20:16:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	greg@...ah.com
Cc:	david-b@...bell.net, linux-usb-users@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: OHCI root_port_reset() deadly loop...

From: Greg KH <greg@...ah.com>
Date: Mon, 8 Oct 2007 20:10:49 -0700

> Yes it does, I'm seeing reports from some hardware companies of the very
> same thing.  If you serialize and load the ehci driver first, and then
> the ohci driver, that should fix the problem.
> 
> Does that also work for you?  Or are these drivers built into the
> kernel?

As coicidence would have it I finally found a recipe for triggering
the issue, and it ties into what you're talking about here.

It happens only if I make sure OHCI gets loaded first and then EHCI
right afterwards.

It seems that indeed it is important for EHCI to get loaded first,
and in-kernel this is ensured by the link ordering.

However, when both OHCI and EHCI are built as modules (or, similarly
I guess, OHCI is built-in and EHCI is modular) there appears to be
nothing in userspace which makes sure EHCI gets loaded first.

When this triggers, in OHCI's root_port_reset(), the port status
register reads 0x111 in that inner-loop and the value never changes.
It stays like this forever.
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