linux-kernel - Re: Clarifying platform_device

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Message-ID: <20080401104533.ZZRA012@mailhub.coreip.homeip.net>
Date:	Tue, 1 Apr 2008 10:54:54 -0400
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Jaya Kumar <jayakumar.lkml@...il.com>,
	Richard Purdie <rpurdie@...ys.net>
Cc:	Linux Kernel Development <linux-kernel@...r.kernel.org>
Subject: Re: Clarifying platform_device_unregister

On Tue, Apr 01, 2008 at 12:47:54AM -0700, Jaya Kumar wrote:
> On Mon, Mar 31, 2008 at 10:19 PM, Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> >  On Mon, Mar 31, 2008 at 09:14:35PM -0400, Jaya Kumar wrote:
> >  >         mytest_device->dev.platform_data = &mydata;
> >
> >  Platform device code does kfree(pdev->dev.platform_data) unpon
> >  unregistration, so it is not a good idea to assign address of
> >  statically-allocated variable here. You should be using:
> >
> >         platform_device_add_data(mytest_device, &mydata, sizeof(mydata));
> >
> 
> That's interesting. I noticed though that a lot of platform device
> code assigns a statically allocated structure to platform_data. For
> example:
> 
> arch/arm/mach-pxa/corgi_pm.c
> static struct sharpsl_charger_machinfo corgi_pm_machinfo = {
> ...
> }
>         corgipm_device->dev.platform_data = &corgi_pm_machinfo;
> 
> same with spitz_pm.c.
> 
> egrep "platform_data.*=.*\&" *.c shows quite a lot of users doing
> that. I guess most of these below are probably okay since these
> drivers can't be rmmoded.
> 

Hmm, are you sure they can't be removed? Why do they all have
module_exit methods?

Even if they can't be unloaded the whole thing will blow to pieces
if registration fails. Consider this:

static int __devinit spitzpm_init(void)
{
        int ret;

        spitzpm_device = platform_device_alloc("sharpsl-pm", -1);
        if (!spitzpm_device)
                return -ENOMEM;

        spitzpm_device->dev.platform_data = &spitz_pm_machinfo;
        ret = platform_device_add(spitzpm_device);

        if (ret)
                platform_device_put(spitzpm_device);
		^^^^^^^^^^^
This will try to kfree(spitzpm_device->dev.platform_data) and it gonna
blow. We need to do spitzpm_device->dev.platform_data = NULL before doing
put.

Also  spitzpm_init() shoudl be marked __init, not __devinit and
spitzpm_exit() should be __exit() if it is event needed at all.

Richard, I think you work with spitz and corgi, any comments?

-- 
Dmitry
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