linux-kernel - Re: [PATCH 5/5] usb_debug: EXPERIMENTAL

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Date:	Thu, 7 May 2009 10:00:15 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Greg KH <greg@...ah.com>
cc:	Jason Wessel <jason.wessel@...driver.com>,
	Oliver Neukum <oliver@...kum.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] usb_debug: EXPERIMENTAL - poll hcd device to
 forcewrites

On Wed, 6 May 2009, Greg KH wrote:

> > If I want to printk from the nmi_watchdog out to this device, am I going
> > to get anything if the write is not synchronous, because in theory the
> > hcd device is never going to get accessed again?
> 
> No you are not, sorry, USB doesn't work without interrupts in this kind
> of mode at all.

This really is an interesting point.  Provided the hardware is 
functioning correctly and enough free memory is available, Jason's 
polling approach would indeed allow USB to work without interrupts -- 
to a limited extent, which is all one needs for console support.  
Especially when the system has just crashed and you want to see that 
final "oops" message...

Alan Stern

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