Re: [PATCH v6 7/8] [media] media: add a debug message to warn about gobj creation/removal

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Mauro,

On Friday 21 August 2015 07:19:21 Mauro Carvalho Chehab wrote:
> Em Fri, 21 Aug 2015 04:32:51 +0300 Laurent Pinchart escreveu:
> > On Wednesday 19 August 2015 08:01:54 Mauro Carvalho Chehab wrote:
> > > It helps to check if the media controller is doing the
> > > right thing with the object creation and removal.
> > > 
> > > No extra code/data will be produced if DEBUG or
> > > CONFIG_DYNAMIC_DEBUG is not enabled.
> > 
> > CONFIG_DYNAMIC_DEBUG is often enabled.
> 
> True, but once a driver/core is properly debugged, images without DEBUG
> could be used in production, if the amount of memory constraints are
> too tight.
> 
> > You're more or less adding function call tracing in this patch, isn't that
> > something that ftrace is supposed to do ?
> 
> Ftrace is a great infrastructure and helps a lot when we need to
> identify bottlenecks and other performance related stuff, but it
> doesn't replace debug functions.
> 
> There are some fundamental differences on what you could do with ftrace
> and what you can't.
> 
> At least on this stage, what I need is something that will provide
> output via serial console when the driver gets loaded, and that provides
> a synchronous output with the other Kernel messages.
> 
> This is the only way to debug certain OOPSes that are happening during
> the development of the patches.
> 
> This is something you cannot do with ftrace, but dynamic DEBUG works
> like a charm.

I understand the need for debug messages during development of a patch series, 
but I don't think this level of debugging belongs to mainline. Debug messages 
for function call tracing, even more in patch 6/8 and 7/8, is frowned upon in 
the kernel.

Or maybe I got it wrong and patches 6/8 and 7/8 are only for development and 
you don't plan to get them in mainline ?

-- 
Regards,

Laurent Pinchart