linux-kernel - Re: [REGRESSION] "USB: use kfifo to buffer usb-generic serial writes" causes gobi

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Date:	Mon, 22 Feb 2010 15:12:41 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Matthew Garrett <mjg59@...f.ucam.org>
cc:	Anssi Hannula <anssi.hannula@....fi>,
	Oliver Neukum <oliver@...kum.org>, <dvomlehn@...co.com>,
	<gregkh@...e.de>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] "USB: use kfifo to buffer usb-generic serial writes"
 causes gobi_loader to hang

On Mon, 22 Feb 2010, Matthew Garrett wrote:

> On Mon, Feb 22, 2010 at 02:10:33PM -0500, Alan Stern wrote:
> > On Mon, 22 Feb 2010, Anssi Hannula wrote:
> > > Does this mean a tty interface is ill-suited for the microcode upload, and 
> > > instead qcserial should use the kernel's generic microcode upload mechanism or 
> > > the userspace should use libusb to do it?
> > 
> > I don't know.  Didn't the old successful code use a tty interface?
> 
> Yes. The kfifo changes have caused some sort of alteration in behaviour.
> 
> > > Any idea what could be causing the hang, then?
> > 
> > No idea, unless it's the device.
> 
> Once the device hangs, it then tends to refuse any input until power 
> cycled. So it's clearly getting into some sort of undefined state, 
> though whether that's because it only gets sent half of its firmware 
> (ie, the hang occurs and as a result the hardware dies) or whether it's 
> causing the hang by dying is unclear.

The latest logs did show all the firmware getting sent -- or at least, 
they show that as much data was sent by the nonworking driver as by the 
working driver.  So I'd say the device causes the hang by dying, 
although I don't know where the hang is or why a dead device should 
cause it.

Alan Stern

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