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

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Date:   Wed, 11 Jan 2017 09:28:37 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        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 03:39:17PM +0100, Uwe Kleine-König wrote:
> 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.
> 
That is what the _or_reset part of devm_add_action_or_reset() is for.

> > >>
> > >> 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;
> 
Yes, Dmitry tried to introduce devm_clk_prepare_enable() some 5 years ago,
but the effort stalled.

My take is that it will be easy to write another coccinelle script to convert
to devm_clk_prepare_enable() once that is available, but I didn't see the point
of waiting for that, especially since it may never happen.

Guenter