linux-kernel - Re: [PATCH] usbcore: Limit number of 'unable to enumerate USB device' messages

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Date:	Fri, 24 Oct 2008 09:57:37 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Larry Finger <Larry.Finger@...inger.net>
cc:	Greg Kroah-Hartman <gregkh@...e.de>, <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usbcore: Limit number of 'unable to enumerate USB device'
 messages

On Thu, 23 Oct 2008, Larry Finger wrote:

> In my system, a number of messages that state "unable to enumerate USB device"
> are logged. These are intermittent and likely due to some race condition
> at bootup.
> 
> Some of these happen when the EHCI driver is loaded after UHCI or OHCI, which
> causes the device to be switched away from the other controller that's trying
> to enumerate it, at least momentarily. This type of message is logged at most
> once for each hub and occurs in about 70% of my reboots.

This is normal; it is caused by userspace loading the drivers in the
wrong order.  ehci-hcd is supposed to be loaded before uhci-hcd or
ohci-hcd, not after.  There's no point trying to change the kernel to
avoid it.

> A more insidious form of the message occurs hundreds of times in about 10% of
> reboots. They continue until the system is rebooted. This patch limits the
> number of these messages to 20. Once the actual cause of this message is
> located, this patch can be reverted.

I would prefer to attack this problem directly rather than wallpaper 
over it.  Can you provide more information?  For example, a dmesg log 
with CONFIG_USB_DEBUG and CONFIG_PRINTK_TIME enabled would help.  It 
might also help to know what the devices which can't be enumerated 
actually are.

Alan Stern

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