linux-kernel - Re: [alsa-devel] [PATCH] ASoC: sgtl5000: Use devm

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Date:	Mon, 07 Jul 2014 17:34:14 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Julia Lawall <julia.lawall@...6.fr>,
	Fabio Estevam <festevam@...il.com>
CC:	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Takashi Iwai <tiwai@...e.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Himangi Saraogi <himangi774@...il.com>
Subject: Re: [alsa-devel] [PATCH] ASoC: sgtl5000: Use devm_ functions

On 07/07/2014 05:23 PM, Julia Lawall wrote:
>
>
> On Mon, 7 Jul 2014, Fabio Estevam wrote:
>
>> On Mon, Jul 7, 2014 at 11:58 AM, Julia Lawall <julia.lawall@...6.fr> wrote:
>>
>>> Nevertheless, there is already a call to devm_regulator_bulk_get in
>>> sgtl5000_enable_regulators which calls sgtl5000_replace_vddd_with_ldo
>>> which calls ldo_regulator_register.  That call was introduced by
>>>
>>> commit 63e54cd9caa3ce03635810608519e2b37d8bc706
>>> Author: Fabio Estevam <fabio.estevam@...escale.com>
>>> Date:   Thu Apr 24 14:13:08 2014 -0300
>>>
>>> It seems that that patch should be reverted?
>>
>> I think so. Russell also reported a kernel oops when unbinding this
>> module, so I will prepare a patch reverting it.
>
> There is documentation about what kinds of devm functions exist, but it is
> too bad that there is no documentation about where they can be used.
> Often there are several levels of function pointers involved, so it can be
> hard to figure out whether they can be used just by looking at the code.
> I have only taken the strategy of using them in kinds of functions where
> someone else has alreadyy figured out that they can be used.

Yes, it is probably a bit underdocumented. The rule of thumb is don't use it 
anywhere else except for device probe callbacks (and functions that are only 
called from a device probe function) and only for the device that is being 
probed. There are probably a couple of instances in the kernel where the 
manged resource allocators are used in places where they shouldn't be used.

- Lars

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