linux-kernel - Re: [PATCH 56/62] watchdog: tangox_wdt: Convert to use device managed functions

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Date:   Wed, 11 Jan 2017 15:39:17 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Marc Gonzalez <marc_gonzalez@...madesigns.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ana.be>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Mans Rullgard <mans@...sr.com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Mark Rutland <mark.rutland@....com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 56/62] watchdog: tangox_wdt: Convert to use device
 managed functions

On Wed, Jan 11, 2017 at 01:31:47PM +0100, Marc Gonzalez wrote:
> On 11/01/2017 11:52, Guenter Roeck wrote:
> 
> > On 01/11/2017 01:07 AM, Marc Gonzalez wrote:
> > 
> >>> @@ -134,12 +134,15 @@ static int tangox_wdt_probe(struct platform_device *pdev)
> >>>  	err = clk_prepare_enable(dev->clk);
> >>>  	if (err)
> >>>  		return err;
> >>> +	err = devm_add_action_or_reset(&pdev->dev,
> >>> +				       (void(*)(void *))clk_disable_unprepare,
> >>> +				       dev->clk);
> >>> +	if (err)
> >>> +		return err;

This looks wrong. There is no clk_unprepare_disable when
devm_add_action_or_reset fails.

> >>
> >> Hello Guenter,
> >>
> >> I would rather avoid the function pointer cast.
> >> How about defining an auxiliary function for the cleanup action?
> >>
> >> clk_disable_unprepare() is static inline, so gcc will have to
> >> define an auxiliary function either way. What do you think?
> > 
> > Not really. It would just make it more complicated to replace the
> > call with devm_clk_prepare_enable(), should it ever find its way
> > into the light of day.
> 
> More complicated, because the cleanup function will have to be deleted later?
> The compiler will warn if someone forgets to do that.
> 
> In my opinion, it's not a good idea to rely on the fact that casting
> void(*)(struct clk *clk) to void(*)(void *) is likely to work as expected
> on most platforms. (It has undefined behavior, strictly speaking.)

I would expect it to work on all (Linux) platforms. Anyhow, I wonder if
there couldn't be found a better solution.

If in the end it looks like the following that would be good I think:

	clk = devm_clk_get(...);
	if (IS_ERR(clk))
		...

	ret = devm_clk_prepare_enable(clk)
	if (ret)
		return ret;

	...

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |