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

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Date:   Sat, 13 Feb 2021 16:59:35 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        mazziesaccount@...il.com
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jean Delvare <jdelvare@...e.com>,
        Mark Gross <mgross@...ux.intel.com>,
        Sebastian Reichel <sre@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Joerg Roedel <jroedel@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-hwmon@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [RFC PATCH 1/7] drivers: base: Add resource managed version of
 delayed work init

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.

> This is the reason why many calls to devm_add_action() point to functions such as
> 
> static void visconti_clk_disable_unprepare(void *data)
> {
>         clk_disable_unprepare(data);
> }
> 
> which could otherwise be handled using typecasts.

Hmm, wouldn't something like this be a candidate for adding a:

devm_clk_prepare_enable() helper?

This seems better then having the driver(s) make + error check separate
clk_prepare_enable() + devm_add_action_or_reset() calls ?

I must admit I'm guilty myself of just using devm_add_action() sometimes
when a specific devm helper is missing, but this whole discussion makes
me think that it would be good to have some extra devm helpers for
common cases / driver cleanup patterns.

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.

Regards,

Hans