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

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Date:	Sat, 17 Jan 2009 16:21:39 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Hiroshi DOYU <Hiroshi.DOYU@...ia.com>
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

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.
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