linux-kernel - Re: [PATCH 2/5] input: twl6040-vibra: add handler to unregister input if module is removed

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Date:	Wed, 20 Apr 2016 11:12:22 +0200
From:	"H. Nikolaus Schaller" <hns@...delico.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Fabio Estevam <fabio.estevam@...escale.com>,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...a-handheld.com, letux-kernel@...nphoenux.org
Subject: Re: [PATCH 2/5] input: twl6040-vibra: add handler to unregister input if module is removed

Hi Dmitry,

> Am 19.04.2016 um 18:53 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
> 
> On Tue, Apr 19, 2016 at 10:05:08AM +0200, H. Nikolaus Schaller wrote:
>> 
>>> Am 19.04.2016 um 09:57 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
>>> 
>>> On Tue, Apr 19, 2016 at 09:33:10AM +0200, H. Nikolaus Schaller wrote:
>>>> 
>>>>> Am 18.04.2016 um 23:12 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
>>>>> 
>>>>> On Mon, Apr 18, 2016 at 09:55:38PM +0200, H. Nikolaus Schaller wrote:
>>>>>> commit 1f9e1470ab34 ("Input: twl6040-vibra - use devm functions")
>>>>>> 
>>>>>> converted everything to devm but we still need to call
>>>>>> input_unregister_device(info->input_dev)
>>>>> 
>>>>> No, this is not needed, because devm-managed input devices will be
>>>>> unregistered automatically.
>>>> 
>>>> Well, it would, if the current driver would use devm for registration. But it appears not to do it that way (line 375):
>>>> 
>>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/input/misc/twl6040-vibra.c?id=refs/tags/v4.6-rc4#n375
>>>> 
>>>> So we either have to fix line 375 or add the proposed explicit unregister call.
>>>> 
>>>> Research shows me that you did propose devm_input_register_device() some years ago but this API was never included:
>>>> 
>>>> https://lkml.org/lkml/2012/10/29/855
>>> 
>>> That's because we have what I mentioned in _OR_ portion of that email:
>>> 
>>> /**
>>> * devm_input_allocate_device - allocate managed input device
>>> * @dev: device owning the input device being created
>>> *
>>> * Returns prepared struct input_dev or %NULL.
>>> *
>>> * Managed input devices do not need to be explicitly unregistered or
>>>                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> * freed as it will be done automatically when owner device unbinds from
>>> * its driver (or binding fails). Once managed input device is allocated,
>>> * it is ready to be set up and registered in the same fashion as regular
>>> * input device. There are no special devm_input_device_[un]register()
>>> * variants, regular ones work with both managed and unmanaged devices,
>>> * should you need them. In most cases however, managed input device need
>>> * not be explicitly unregistered or freed.
>>> *
>>> * NOTE: the owner device is set up as parent of input device and users
>>> * should not override it.
>>> */
>>> 
>> 
>> Hm. If I remember correctly (it is a while ago) we had to add this explicit
>> unregister mechanism because we got ugly kernel panics otherwise. Indicating
>> that the input device was still registered and *not* unregistered automatically.
> 
> Ah, it is probably because we are messing up with input device's parent.
> Can you please try the patch below?
> 

Appears to have no new side-effects and the original problem does not appear again.

BR and thanks,
Nikolaus