linux-kernel - Re: Dynamic debug on by default?

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Message-ID: <20130814170410.GA7668@kroah.com>
Date:	Wed, 14 Aug 2013 10:04:10 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Xenia Ragiadakou <burzalodowa@...il.com>,
	Jason Baron <jbaron@...mai.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Dynamic debug on by default?

On Wed, Aug 14, 2013 at 09:51:54AM -0700, Joe Perches wrote:
> On Wed, 2013-08-14 at 09:40 -0700, Sarah Sharp wrote:
> > Hi Xenia,
> > 
> > I'm a bit confused.  I thought that debugging messages would be turned
> > off by default for a module if CONFIG_DYNAMIC_DEBUG was turned on.  When
> > I tested your patch to remove the CONFIG_USB_XHCI_HCD_DEBUGGING and just
> > use dev_dbg, the messages from the xHCI driver appeared in dmesg by
> > default.
> > 
> > That generates a lot of log spew.  We can have distros add a boot
> > parameter option to turn off debug messages, but that boot parameter is
> > limited to 1023 characters.  I'm concerned that if more drivers add
> > dynamic debugging, the distros will eventually run out of space in the
> > dynamic debugging boot parameter.  I know Greg was ripping out debugging
> > config options in other USB drivers, so this is a bit concerning.
> > 
> > Jason, is there a way within the xHCI driver to say that dynamic
> > debugging should be off by default?  I've looked through the
> > documentation, and I can't find anything like that documented.
> 
> #undefine DEBUG
> 
> > I've attached my .config file, in case I have something misconfigured.
> 
> Because of:
> 
> drivers/usb/host/Makefile:ccflags-$(CONFIG_USB_DEBUG) := -DDEBUG

Yes, that's the problem, I'm trying to get rid of the CONFIG_USB_DEBUG
flag, and I'm almost there.  There are some host controllers that still
use it for some things that I have not cleaned up fully yet.

thanks,

greg k-h
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