linux-kernel - Re: A really interesting mass-storage BUG introduced after 2.6.18

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Date:	Thu, 15 Jan 2009 10:13:37 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	ozan@...dus.org.tr, Iwo Mergler <iwo@...l-direct.com.au>
cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: A really interesting mass-storage BUG introduced after 2.6.18

On Thu, 15 Jan 2009, Iwo Mergler wrote:

> > 
> > This shows the computer sending a TEST UNIT READY command to the drive, 
> > and the drive reporting Unit Attention: Media not present.  So of 
> > course Linux believes there is no media loaded in the drive and doesn't 
> > try to read the partition table or anything else.
> > 
> > Presumably if the drive is plugged in during bootup then the BIOS does 
> > something to make this error status go away.  It's hard to guess what 
> > that would be, however.
> > 
> 
> It could be a matter of timing. Some badly designed USB devices have a
> dead time between power-up and being ready, but show up on the bus as
> if they where. The "Media not present" thing could be a symptom of this.

Good point.

> To verify it, try inserting the device slowly. The power contacts in
> the USB connector are longer than the data contacts and the device gets
> more time to boot.

Another timing-sensitive values you can set is the delay_use module
parameter for usb-storage.  It defaults to 5 seconds but perhaps you
need a longer delay.

Alan Stern

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