Re: [PATCH] of: provide of_platform_unpopulate()

[Rob Herring <robherring2@gmail.com>]

On 07/21/2013 06:44 PM, Grant Likely wrote:
> 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.

Was there more breakage than imx6 and amba devices? Your first version
had a fallback case for powerpc. Couldn't we do just allow that for more
than just powerpc? I'd much rather see some work-around within the core
DT code with a warning to prevent more proliferation than putting this
into drivers.

Rob