linux-kernel - Re: ehci dynamic debug problem

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Date:	Fri, 13 Apr 2012 14:13:58 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Johannes Stezenbach <js@...21.net>
cc:	Jason Baron <jbaron@...hat.com>, <linux-kernel@...r.kernel.org>,
	<linux-usb@...r.kernel.org>
Subject: Re: ehci dynamic debug problem

On Fri, 13 Apr 2012, Johannes Stezenbach wrote:

> > But there is no such thing as dynamic debug for ehci, is there?  
> > There's a separate dynamic debug setting for each dev_dbg statement.
> > So your ideal solution makes no sense.
> 
> When CONFIG_DYNAMIC_DEBUG=y but ehci debug is disabled

There is no such thing as ehci debug!  So how can it be disabled?
There's only an individual setting for each line of debugging code.

> in /sys/kernel/debug/dynamic_debug/control, then
> dbg_port() calls dbg_port_buf() which would
> format the string, then calls ehci_dbg() which
> calls dev_dbg() which discards it.
> 
> Does it make sense now?

No.  What happens if dynamic debug is enabled for one line that calls 
dbg_port_buf() but not for another?  There's no way to avoid the string 
formatting in both lines, even though one of them discards the result.

Alan Stern

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