linux-kernel - Re: Using statically allocated memory for platform

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Message-ID: <20091102155231.GC20341@fluff.org.uk>
Date:	Mon, 2 Nov 2009 15:52:31 +0000
From:	Ben Dooks <ben-linux@...ff.org>
To:	Ben Dooks <ben-linux@...ff.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Antonio Ospite <ospite@...denti.unina.it>,
	openezx-devel@...ts.openezx.org,
	Samuel Ortiz <sameo@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Mike Rapoport <mike@...pulab.co.il>,
	Daniel Ribeiro <drwyrm@...il.com>
Subject: Re: Using statically allocated memory for platform_data.

On Mon, Nov 02, 2009 at 03:25:00PM +0000, Ben Dooks wrote:
> On Mon, Nov 02, 2009 at 03:05:25PM +0000, Russell King - ARM Linux wrote:
> > On Mon, Nov 02, 2009 at 03:00:11PM +0000, Ben Dooks wrote:
> > > This looks like something is freeing stuff that it did not allocate in
> > > the first place, which is IMHO bad. The call platform_device_alloc()
> > > is setting platform_device_release() as the default release function
> > > but platform_device_release() releases more than platform_device_alloc()
> > > actually created.
> > > 
> > > My view is that platform_device_alloc()'s default release shouldn't
> > > be freeing the platform data, and that using platform_device_add_data()
> > > or platform_device_add_resources() should change either the behvaiour 
> > > of platform_device_release() or it should change the pointer to a new
> > > release function.
> > 
> > That doesn't work - how do those other functions (adding) know what data
> > has also been added by other functions?  That can't work reliably.
> 
> You could wrapper platform device, and each of the add functions could
> update it, but that would assume the platform device had been allocated
> with platform_device_alloc().

Having had a look, all the current users of platform_device_add_data()
are from a platform_alloc_device() created device. 

The number of calls to platform_device_add_resources() are many, but
the ones I checked are from platform_alloc_device().

However your point being that these add calls may not be used on a
device that has been created from platform_device_alloc() is one I
overlooked.

Having a state machine that changed the release call from
platform_device_release() to say platform_device_release_resources()
or platform_device_release_all() and then platform_device_release_all()
may be another way to do it.

-- 
Ben (ben@...ff.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'
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