linux-kernel - Re: [RFC PATCH 1/7] drivers: base: Add resource managed version of delayed work init

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Date:   Mon, 15 Feb 2021 11:37:26 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>
Cc:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
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        "bgolaszewski@...libre.com" <bgolaszewski@...libre.com>,
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        "sre@...nel.org" <sre@...nel.org>,
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Subject: Re: [RFC PATCH 1/7] drivers: base: Add resource managed version of
 delayed work init

Hi,

On 2/15/21 8:22 AM, Vaittinen, Matti wrote:
> 
> On Sat, 2021-02-13 at 16:59 +0100, Hans de Goede wrote:
>> Hi,
>>
>> On 2/13/21 4:27 PM, Guenter Roeck wrote:
>>> On 2/13/21 7:03 AM, Hans de Goede wrote:
>>> [ ... ]
>>>> I think something like this should work:
>>>>
>>>> static int devm_delayed_work_autocancel(struct device *dev,
>>>> struct delayed_work *w,
>>>> 					void (*worker)(struct
>>>> work_struct *work)) {
>>>> 	INIT_DELAYED_WORK(w, worker);
>>>> 	return devm_add_action(dev, (void (*action)(void
>>>> *))cancel_delayed_work_sync, w);
>>>> }
>>>>
>>>> I'm not sure about the cast, that may need something like this
>>>> instead:
>>>>
>>>> typedef void (*devm_action_func)(void *);
>>>>
>>>> static int devm_delayed_work_autocancel(struct device *dev,
>>>> struct delayed_work *w,
>>>> 					void (*worker)(struct
>>>> work_struct *work)) {
>>>> 	INIT_DELAYED_WORK(w, worker);
>>>> 	return devm_add_action(dev,
>>>> (devm_action_func)cancel_delayed_work_sync, w);
>>>
>>> Unfortunately, you can not type cast function pointers in C. It is
>>> against the C ABI.
>>> I am sure it is done in a few places in the kernel anyway, but
>>> those are wrong.
>>
>> I see, bummer.
> 
> I think using devm_add_action() is still a good idea.

Yes, we could also just have a 1 line static inline function to do
the function-cast. Like this:

static inline void devm_delayed_work_autocancel_func(void *work)
{
	cancel_delayed_work_sync(work);
}

static inline int devm_delayed_work_autocancel(struct device *dev, struct delayed_work *w, void (*worker)(struct work_struct *work))
{
	INIT_DELAYED_WORK(w, worker);
	return devm_add_action(dev, devm_delayed_work_autocancel_func, w);
}

Both functions will then simply be compiled out in files which do not
use them.

>> If we add a devm_clk_prepare_enable() helper that should probably be
>> added
>> to drivers/clk/clk-devres.c and not to drivers/base/devres.c .
>>
>> I also still wonder if we cannot find a better place for this new
>> devm_delayed_work_autocancel() helper but nothing comes to mind.
> 
> I don't like the idea of including device.h from workqueue.h - and I
> think this would be necessary if we added
> devm_delayed_work_autocancel() as inline in workqueue.h, right?

Yes.

> I also see strong objection towards the devm managed clean-ups.

Yes it seems that there are some people who don't like this, where as
others do like them.

> How about adding some devm-helpers.c in drivers/base - where we could
> collect devm-based helpers - and which could be enabled by own CONFIG -
> and left out by those who dislike it?

I would make this something configurable through Kconfig, but if
go the static inline route, which I'm in favor of then we could just
have a:

include/linux/devm-cleanup-helpers.h

And put everything (including kdoc texts) there.

This way the functionality is 100% opt-in (by explicitly including
the header if you want the helpers) which hopefully makes this a
bit more acceptable to people who don't like this style of cleanups.

I would be even happy to act as the upstream maintainer for such a
include/linux/devm-cleanup-helpers.h file, I can maintain it as part
of the platform-drivers-x86 tree (with its own MAINTAINERS entry).

Greg, would this be an acceptable solution to you ?

Regards,

Hans