linux-kernel - Re: driver probe error reporting

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Date:	Wed, 17 Dec 2008 13:53:20 -0800
From:	Greg KH <greg@...ah.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Ben Dooks <ben-linux@...ff.org>, linux-kernel@...r.kernel.org
Subject: Re: driver probe error reporting

On Wed, Dec 17, 2008 at 10:44:34PM +0100, Rafael J. Wysocki wrote:
> On Wednesday, 17 of December 2008, Greg KH wrote:
> > On Wed, Dec 17, 2008 at 01:44:52PM +0100, Rafael J. Wysocki wrote:
> > > On Wednesday, 17 of December 2008, Greg KH wrote:
> > > > On Mon, Dec 15, 2008 at 11:15:02PM +0000, Ben Dooks wrote:
> > > > > This runs on from the discussion in [1] on how drivers (especially
> > > > > one using a variant of the device driver framework) report errors
> > > > > on probe. There are two main classes of errors, the type which happen
> > > > > at probe time (device not responding, not enough memory, etc) and
> > > > > errors that are due to configuration such as missing device configuration
> > > > > data.
> > > > > 
> > > > > It has been suggested that using dev_err() to report any configuration
> > > > > data error is a bloat of code as a properly debugged kernel should never
> > > > > find itself in this state.
> > > > > 
> > > > > Unfortunatley the only diagnostic dev_xxx() macro is dev_dbg() which is
> > > > > only available if the the driver code itself defines DEBUG. I would think
> > > > > it would be better to have a macro that can be turned on/off by a kernel
> > > > > configuration for when debugging which turns on the messages that are
> > > > > important to developers creating new machine/arch support but disabled
> > > > > for shipping kernels.
> > > > 
> > > > Not anymore, dev_dbg() can be dynamically switched on and off at runtime
> > > > in 2.6.28.
> > > 
> > > IMO, there's a problem with that, because it turns on _all_ of the debug info
> > > from the entire kernel, which is _never_ necessary.
> > 
> > No, it is turned on and off on a per-module basis, not for the whole
> > kernel (although that is possible if you so desire.)
> > 
> > So this should not be an issue.
> 
> Well, recently I've been debugging suspend-resume quite a lot and I had to
> compile it out.  I use verbose PM debugging for that, which is based on
> dev_dbg(), and it is very inconvenient with dynamic printk.

I'm confused, if you enable dynamic printk, it uses dev_dbg().  And then
you can turn it on or off on a per-module basis.

What are you suggesting we do instead?

thanks,

greg k-h
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