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

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Date:	Tue, 19 Apr 2016 09:53:25 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"H. Nikolaus Schaller" <hns@...delico.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

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?

Thanks.

-- 
Dmitry


Input: twl6040-vibra - do not reparent to grandparent

From: Dmitry Torokhov <dmitry.torokhov@...il.com>

For devm-managed input devices we should not modify input device's parent,
otherwise automatic release of resources will not work properly.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
---
 drivers/input/misc/twl6040-vibra.c |    1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/input/misc/twl6040-vibra.c b/drivers/input/misc/twl6040-vibra.c
index 0c853c2..53e33fa 100644
--- a/drivers/input/misc/twl6040-vibra.c
+++ b/drivers/input/misc/twl6040-vibra.c
@@ -357,7 +357,6 @@ static int twl6040_vibra_probe(struct platform_device *pdev)
 
 	info->input_dev->name = "twl6040:vibrator";
 	info->input_dev->id.version = 1;
-	info->input_dev->dev.parent = pdev->dev.parent;
 	info->input_dev->close = twl6040_vibra_close;
 	__set_bit(FF_RUMBLE, info->input_dev->ffbit);