linux-kernel - Re: [PATCH v2 1/3] pwm: Add pwm_cansleep() as exported API to users

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Message-ID: <20130128095754.GA23134@avionic-0098.adnet.avionic-design.de>
Date:	Mon, 28 Jan 2013 10:57:54 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Florian Vaussard <florian.vaussard@...l.ch>
Cc:	Peter Ujfalusi <peter.ujfalusi@...com>,
	Bryan Wu <cooloney@...il.com>,
	Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] pwm: Add pwm_cansleep() as exported API to users

On Mon, Jan 28, 2013 at 10:36:07AM +0100, Florian Vaussard wrote:
> Hello,
> 
> Le 28/01/2013 09:45, Peter Ujfalusi a écrit :
> >hi Thierry,
> >
> >On 01/26/2013 06:40 AM, Thierry Reding wrote:
[...]
> >>>+{
> >>>+	return pwm->chip->can_sleep;
> >>>+}
> >>>+EXPORT_SYMBOL_GPL(pwm_cansleep);
> >>
> >>Would it make sense to check for NULL pointers here? I guess that
> >>passing NULL into the function could be considered a programming error
> >>and an oops would be okay, but in that case there's no point in making
> >>the function return an int. Also see my next comment.
> >
> >While it is unlikely to happen it is better to be safe, something like this
> >will do:
> >
> >return pwm ? pwm->chip->can_sleep : 0;
> >
> 
> Ok. And what about:
> 
> BUG_ON(pwm == NULL);
> return pwm->chip->can_sleep;

I don't think we need that. In case pwm == NULL, dereferencing it will
oops anyway. So either we make it safe and return an error code, or we
let it oops without explicit BUG_ON().

Thierry

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