linux-kernel - Re: [PATCH v2] [media] v4l: omap4iss: Add DEBUG compiler flag

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Date:	Thu, 06 Mar 2014 12:00:30 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Joe Perches <joe@...ches.com>, devel@...verdev.osuosl.org,
	Paul Bolle <pebolle@...cali.nl>, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH v2] [media] v4l: omap4iss: Add DEBUG compiler flag

Hi Greg,

On Wednesday 05 March 2014 20:45:29 Greg Kroah-Hartman wrote:
> On Thu, Mar 06, 2014 at 01:48:29AM +0100, Laurent Pinchart wrote:
> > On Wednesday 05 March 2014 16:28:03 Joe Perches wrote:
> > > On Thu, 2014-03-06 at 00:50 +0100, Laurent Pinchart wrote:
> > > > Please note that -DDEBUG is equivalent to '#define DEBUG', not to
> > > > '#define CONFIG_DEBUG'. 'DEBUG' needs to be defined for dev_dbg() to
> > > > have any effect.
> > > 
> > > Not quite.  If CONFIG_DYNAMIC_DEBUG is set, these
> > > dev_dbg statements are compiled in but not by default
> > > set to emit output.  Output can be enabled by using
> > > dynamic_debug controls like:
> > > 
> > > # echo -n 'file omap4iss/* +p' > <debugfs>/dynamic_debug/control
> > > 
> > > See Documentation/dynamic-debug-howto.txt for more details.
> > 
> > Thank you for the additional information.
> > 
> > Would you recommend to drop driver-specific Kconfig options related to
> > debugging and use CONFIG_DYNAMIC_DEBUG instead ?
> 
> Yes, please do that, no one wants to rebuild drivers and subsystems with
> different options just for debugging.

Is CONFIG_DYNAMIC_DEBUG lean enough to be used on embedded systems ? Note that 
people would still have to rebuild their kernel to enable CONFIG_DYNAMIC_DEBUG 
anyway :-)

-- 
Regards,

Laurent Pinchart

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