linux-kernel - Re: platform_device_add

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Message-ID: <20091026212132.GA11973@suse.de>
Date:	Mon, 26 Oct 2009 14:21:32 -0700
From:	Greg KH <gregkh@...e.de>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Russell King <rmk+kernel@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: platform_device_add_data(pdev, NULL, 0)

On Mon, Oct 26, 2009 at 10:19:03PM +0100, Uwe Kleine-König wrote:
> Hi Greg,
> 
> On Mon, Oct 26, 2009 at 09:48:07AM -0700, Greg KH wrote:
> > On Fri, Oct 23, 2009 at 10:26:22PM +0200, Uwe Kleine-König wrote:
> > > Hello,
> > > 
> > > mfd_add_device() (defined in drivers/mfd/mfd-core.c) is a wrapper do
> > > allocate platform_devices.
> > > 
> > > It contains:
> > > 
> > > 	ret = platform_device_add_data(pdev,
> > > 			cell->platform_data, cell->data_size);
> > > 
> > > If cell->data_size is 0 (and so likely cell->platform_data == NULL),
> > > still pdev->dev.platform_data get assigned ZERO_SIZE_PTR.
> > > 
> > > IMHO the result should better be that pdev->dev.platform_data ends being
> > > NULL, too.  Agreed?
> > 
> > Why?  Is this causing problems somewhere?
> The "problem" I as follows:  I have a driver that doesn't use
> platform_data and I want to change that.  As both the driver and the
> device probably go via different trees and I want to do the following in
> the driver:
> 
> 	if (platform_data != NULL)
> 		/* use it */
> 	else
> 		/* use the old data */
> 
> OK, I could simply use:
> 
> 	if (platform_data != NULL && platform_data != ZERO_SIZE_PTR)
> 		...
> 
> but it feels ugly.

Yes, that would be ugly.  How about just sending the driver and device
through the same trees to prevent this from happening?

thanks,

greg k-h
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