CONFIG_VIDEO_ADV_DEBUG question

CONFIG_VIDEO_ADV_DEBUG question

[Hans de Goede]

Hi All,

CONFIG_VIDEO_ADV_DEBUG enables additional debugging output in the gscpa 
driver, which then becomes "active" when a module option gets passed. So 
in the gspca case it normally only results in a larger driver without 
causing additional debug unless module option is passed.

I've been asking the Fedora kernel maintainers to enable this option by 
default for the Fedora development version atleast, and thus I wonder 
how this option affects other drivers, are there other drivers which 
become very chatty with this option, or do they all need a module option 
to truely enable all the debug spew like gspca?

Regards,

Hans

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Re: CONFIG_VIDEO_ADV_DEBUG question

[Hans Verkuil]

> Hi All,
>
> CONFIG_VIDEO_ADV_DEBUG enables additional debugging output in the gscpa
> driver, which then becomes "active" when a module option gets passed. So
> in the gspca case it normally only results in a larger driver without
> causing additional debug unless module option is passed.
>
> I've been asking the Fedora kernel maintainers to enable this option by
> default for the Fedora development version atleast, and thus I wonder
> how this option affects other drivers, are there other drivers which
> become very chatty with this option, or do they all need a module option
> to truely enable all the debug spew like gspca?

The verbosity level is done through some sort of debug module option. This
CONFIG is only used AFAIK to enable the VIDIOC_DBG_G/S_REGISTER ioctls
which allows you to program the video device(s) directly by
setting/getting registers.

I see that a few drivers use it to expose extra information through sysfs.

But the way gspca uses it is not correct. I would remove the test on
CONFIG_VIDEO_ADV_DEBUG there altogether, or replace it with a test of a
new gspca-specific config option. The ADV_DEBUG option is really about
allowing the root user access to low-level driver registers through the
v4l2-dbg utility. It's not about enabling additional debugging output.

This is also the reason by it is disabled by most (?) distros: it's a bit
dangerous to allow the user to mess with that. But it is ideal to test
different register values on the fly.

Regards,

         Hans

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Re: CONFIG_VIDEO_ADV_DEBUG question

[Jean-Francois Moine]

On Tue, 2008-07-29 at 14:10 +0200, Hans Verkuil wrote:
> Hans de Goede wrote:
> > CONFIG_VIDEO_ADV_DEBUG enables additional debugging output in the gscpa
> > driver, which then becomes "active" when a module option gets passed. So
> 	[snip]
> But the way gspca uses it is not correct. I would remove the test on
> CONFIG_VIDEO_ADV_DEBUG there altogether, or replace it with a test of a

Hello Hans and Hans,

OK. So I see 3 options:
1) add a new kernel config option, say CONFIG_GSPCA_DEBUG,
2) always set an internal compile option GSPCA_DEBUG,
3) have the option GSPCA_DEBUG, but unset by default.

Which is the best for you, Hans (de Goede)?

Cheers.

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Ken ar c'hentañ |             ** Breizh ha Linux atav! **
Jef             |               http://moinejf.free.fr/


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Re: CONFIG_VIDEO_ADV_DEBUG question

[Hans de Goede]

Jean-Francois Moine wrote:
> On Tue, 2008-07-29 at 14:10 +0200, Hans Verkuil wrote:
>> Hans de Goede wrote:
>>> CONFIG_VIDEO_ADV_DEBUG enables additional debugging output in the gscpa
>>> driver, which then becomes "active" when a module option gets passed. So
>> 	[snip]
>> But the way gspca uses it is not correct. I would remove the test on
>> CONFIG_VIDEO_ADV_DEBUG there altogether, or replace it with a test of a
> 
> Hello Hans and Hans,
> 
> OK. So I see 3 options:
> 1) add a new kernel config option, say CONFIG_GSPCA_DEBUG,
> 2) always set an internal compile option GSPCA_DEBUG,
> 3) have the option GSPCA_DEBUG, but unset by default.
> 
> Which is the best for you, Hans (de Goede)?
> 

My vote goes to 2, so that when users using distro kernels (which will soon 
have gspca v2, Fedora's development kernel already has it) we can tell them to 
add the necessary module option and get debug output from them without them 
having to rebuild a kernel (module).

Regards,

Hans

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