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

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Message-Id: <20091103183154.ee6b5676.ospite@studenti.unina.it>
Date:	Tue, 3 Nov 2009 18:31:54 +0100
From:	Antonio Ospite <ospite@...denti.unina.it>
To:	Ben Dooks <ben-linux@...ff.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	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, 2 Nov 2009 16:47:44 +0000
Ben Dooks <ben-linux@...ff.org> wrote:

> On Mon, Nov 02, 2009 at 04:37:01PM +0000, Russell King - ARM Linux wrote:
> > On Mon, Nov 02, 2009 at 04:28:39PM +0000, Ben Dooks wrote:
> > > On Mon, Nov 02, 2009 at 03:56:25PM +0000, Russell King - ARM Linux wrote:
> > > > The reason we have platform_device_add_data() is that people think that
> > > > the device data needs to persist for the lifetime of the device.  I
> > > > personally disagree with that - once you unregister the device, it's
> > > > guaranteed that device drivers will have been unregistered, so who's
> > > > going to use the platform data?
> > > 
> > > That doesn't make any sense, in the current case of using the
> > > platform_device_alloc() and those calls the data is only living
> > > for the lifetime of the device, as the release call is tidying up
> > > the result.
> > 
> > What I'm saying is that the lifetime of the data finishes once
> > the _unregister() call has returned.  So:
> > 
> > 	data = pdev->dev.platform_data;
> > 	platform_device_unregister(pdev);
> > 	kfree(data);
> > 
> > is an entirely valid way of handling the "I allocated my platform
> > data" problem - it doesn't need to exist to the point where the
> > device itself is freed.
> 
> Unforutnately pretty much everyone now assumes that the act of
> unregistering the device will get rid of the data that the allocated
> by the add functions.
> 
> This would mean going around fixing a number of current drivers which
> all make that assumption.
> 

So those drivers (ezx-pcap.c, da903x.c) aren't doing anything manifestly
wrong by not calling platform_device_add_data(), and the issue will be
solved in ./drivers/base/platform.c someway eventually, right?

Thanks,
   Antonio

-- 
Antonio Ospite
http://ao2.it

PGP public key ID: 0x4553B001

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