linux-kernel - Re: [PATCH 3/6] omap iommu: omap3 iommu device registration

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Date:	Tue, 27 Jan 2009 23:29:35 +0200 (EET)
From:	Hiroshi DOYU <Hiroshi.DOYU@...ia.com>
To:	linux@....linux.org.uk
Cc:	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.arm.linux.org.uk, linux-omap@...r.kernel.org
Subject: Re: [PATCH 3/6] omap iommu: omap3 iommu device registration

Hi Russell,

I attached the update one.

From: ext Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Re: [PATCH 3/6] omap iommu: omap3 iommu device registration
Date: Sat, 17 Jan 2009 17:21:39 +0100

> On Fri, Jan 16, 2009 at 10:37:20AM +0200, Hiroshi DOYU wrote:
> > +#include <linux/io.h>
> 
> Is linux/io.h needed, or will a more specific include be better?
> 
> > +#include <linux/platform_device.h>
> > +
> > +#include <mach/iommu.h>
> > +
> > +#define DEVNAME "omap-iommu"
> 
> I'm not sure this DEVNAME definition really helps anything.
> 
> > +static void omap3_iommu_release(struct device *dev)
> > +{
> > +}
> 
> Err, no.  Never ever ever provide a NULL release function.  Providing
> such a function is a screaming message that what you're doing is buggy.
> 
> And if you get a warning through not providing such a function, it's
> telling you that what your overall approach with the driver API is
> buggy (and you haven't understood the implications of refcounted
> object management.)
> 
> > +
> > +static struct platform_device omap3_iommu_pdev[] = {
> > +	{
> > +		.name		= DEVNAME,
> > +		.id		= 1,
> > +		.num_resources	= ARRAY_SIZE(iommu1_res),
> > +		.resource	= iommu1_res,
> > +		.dev		= {
> > +			.release = omap3_iommu_release,
> > +			.platform_data = &omap3_iommu_pdata[0],
> > +		},
> > +	},
> > +	{
> > +		.name		= DEVNAME,
> > +		.id		= 2,
> > +		.num_resources	= ARRAY_SIZE(iommu2_res),
> > +		.resource	= iommu2_res,
> > +		.dev		= {
> > +			.release = omap3_iommu_release,
> > +			.platform_data = &omap3_iommu_pdata[1],
> > +		},
> > +	},
> > +};
> > +
> > +static int __init omap3_iommu_init(void)
> > +{
> > +	int i;
> > +	for (i = 0; i < ARRAY_SIZE(omap3_iommu_pdev); i++)
> > +		platform_device_register(&omap3_iommu_pdev[i]);
> > +	return 0;
> > +}
> > +module_init(omap3_iommu_init);
> > +
> > +static void __exit omap3_iommu_exit(void)
> > +{
> > +	int i;
> > +	for (i = 0; i < ARRAY_SIZE(omap3_iommu_pdev); i++)
> > +		platform_device_unregister(&omap3_iommu_pdev[i]);
> 
> So... this can never be bug free - you can _never_ unregister statically
> allocated devices.  Not even if you provide an empty release function.
> 
> If you want to register and unregister device structures, it must be
> done using the correct APIs, and in the case of platform devices, that's
> the platform_device_alloc(), platform_device_add() and
> platform_device_unregister() APIs.

View attachment "0003-omap-iommu-omap3-iommu-device-registration.patch" of type "Text/Plain" (3149 bytes)