linux-kernel - Re: [GPIO]implement sleeping GPIO chip removal

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Message-ID: <20101110231507.GA6758@linux-sh.org>
Date:	Thu, 11 Nov 2010 08:15:08 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Greg KH <gregkh@...e.de>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maciej Szmigiero <mhej@...pl>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org,
	Anton Vorontsov <avorontsov@...mvista.com>,
	Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Cameron <jic23@....ac.uk>,
	Ben Nizette <bn@...sdigital.com>
Subject: Re: [GPIO]implement sleeping GPIO chip removal

On Wed, Nov 10, 2010 at 02:45:16PM -0800, Greg KH wrote:
> On Wed, Nov 10, 2010 at 02:15:40PM -0700, Grant Likely wrote:
> > On Wed, Nov 10, 2010 at 10:07:05PM +0100, Thomas Gleixner wrote:
> > > > I understand that it could be simplified by removing redundant code
> > > > (as Grant Likely had suggested before), and moving it to completion
> > > > interface instead of manipulating a task structure directly, but
> > > > this doesn't mean that the whole GPIO code has to be rewritten just
> > > > to add one functionality.
> > > 
> > > It's not about rewriting, it's about fixing the problem in the right
> > > way and not just hacking around it.
> > > 
> > > If we see a shortcoming like this, we fix it and do not magically work
> > > around it.
> > 
> > +1
> > 
> > Thomas is right.  kobject reference counting is the correct solution.
> > Nack on this approach.
> 
> Only use a kobject if you want to be in the sysfs hierarchy (which I
> don't think you want to do here.)  If you want proper reference
> counting, use a 'struct kref' instead.
> 
This is actually an interesting problem. The gpiolib code presently has
its own hand-rolled sysfs support, which is entirely optional. If someone
is going to go through and do some refactoring anyways it would be
worthwile to see how much tidying up using a kobject would permit. 
kobject-based refcounting could in effect be used like kref-refcounting
with the sysfs interface disabled, too.
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