linux-kernel - Re: [Linux-usb-users] OHCI root_port

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Message-Id: <20071015233910.5A17123BC99@adsl-69-226-248-13.dsl.pltn13.pacbell.net>
Date:	Mon, 15 Oct 2007 16:39:10 -0700
From:	David Brownell <david-b@...bell.net>
To:	davem@...emloft.net
Cc:	stern@...land.harvard.edu, linux-usb-users@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, greg@...ah.com
Subject: Re: [Linux-usb-users] OHCI root_port_reset() deadly loop...

> Bad news, even with the rwsem after a lot more testing I can still
> trigger the hang in ohci_hub_control() :-(
>
> I think we need to go back to considering the total serialization
> approach to this problem.

We shouldn't need that.  What happens if you add an msleep(5)
before ehci-hcd::ehci_run() drops ehci_cf_port_reset_rwsem?

The theory there being that the switch triggered by setting CF
doesn't take effect instantaneously, contrary to the effective
assumption of that code.  A delay of 5 msec seems like it should
be more than enough, but that's kind of a guess ... it's good to
keep that low, since unfortunately that's in the critical path
for OLPC "resume from idle".

- Dave

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