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From: Grant Likely <grant.likely@linaro.org>
Date: Mon, 22 Jul 2013 00:44:27 +0100
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Subject: Re: [PATCH] of: provide of_platform_unpopulate()
To: Rob Herring <robherring2@gmail.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Rob Herring <rob.herring@calxeda.com>,
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On Sun, Jul 21, 2013 at 9:48 PM, Rob Herring <robherring2@gmail.com> wrote:
> On 07/21/2013 09:42 AM, Rob Herring wrote:
>> On 07/19/2013 01:14 PM, Sebastian Andrzej Siewior wrote:
>>> So I called of_platform_populate() on a device to get each child device
>>> probed and on rmmod and I need to reverse its doing. After a quick grep
>>> I did what others did as well and rmmod ended in:
>>>
>>> | Unable to handle kernel NULL pointer dereference at virtual address 00000018
>>> | PC is at release_resource+0x18/0x80
>>> | Process rmmod (pid: 2005, stack limit = 0xedc30238)
>>> | [<c003add0>] (release_resource+0x18/0x80) from [<c0300e08>] (platform_device_del+0x78/0xac)
>>> | [<c0300e08>] (platform_device_del+0x78/0xac) from [<c0301358>] (platform_device_unregister+0xc/0x18)
>>>
>>> The problem is that platform_device_del() "releases" each ressource in its
>>> tree. This does not work on platform_devices created by OF becuase they
>>> were never added via insert_resource(). As a consequence old->parent in
>>> __release_resource() is NULL and we explode while accessing ->child.
>>> So I either I do something completly wrong _or_ nobody here tested the
>>> rmmod path of their driver.
>>
>> Wouldn't the correct fix be to call insert_resource somehow? The problem
>> I have is that while of_platform_populate is all about parsing the DT
>> and creating devices, the removal side has nothing to do with DT. So
>> this should not be in the DT code. I think the core device code should
>> be able to handle removal if the device creation side is done correctly.
>>
>> It looks to me like of_device_add either needs to call
>> platform_device_add rather than device_add. I think the device name
>> setting in platform_device_add should be a nop. If not, a check that the
>> name is already set could be added.
>>
>
> BTW, it looks like Grant has attempted this already:

Yup, things broke badly. Unfortunately the of_platform_device and
platform_device history doesn't treat resources in the same way. I
would like to merge the code, but I haven't been able to figure out a
clean way to do it. Looks like we do need the unpopulate function.

g.
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