linux-kernel - Re: [PWM PATCH 2/5] Emulates PWM hardware using a high-resolution timer and a GPIO pin

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Date:	Fri, 12 Feb 2010 14:41:04 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Stanislav O. Bezzubtsev" <stas@....cs.msu.su>
Cc:	Bill Gatliff <bgat@...lgatliff.com>,
	linux-embedded@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PWM PATCH 2/5] Emulates PWM hardware using a high-resolution
	timer and a GPIO pin

> 
> 11.02.2010, ? 23:58, Pavel Machek ???????(?):
> 
> > On Thu 2010-02-11 14:35:14, Bill Gatliff wrote:
> >> Pavel Machek wrote:
> >>>> +static void
> >>>> +gpio_pwm_work (struct work_struct *work)
> >>>> +{
> >>>> +	struct gpio_pwm *gp = container_of(work, struct gpio_pwm, work);
> >>>> +
> >>>> +	if (gp->active)
> >>>> +		gpio_direction_output(gp->gpio, gp->polarity ? 1 : 0);
> >>>> +	else
> >>>> +		gpio_direction_output(gp->gpio, gp->polarity ? 0 : 1);
> >>>> +}
> >>>> 
> >>> 
> >>> ...polarity ^ active ?
> >>> 
> >> 
> >> ... except that if polarity and/or active are >1, I don't send the
> >> values 1 or 0 to gpio_direction_output.  I don't know if the API is
> >> specifically intended to accept nonzero values that are greater than 1.
> > 
> > !polarity ^ !active ? :-).
> 
> 
> One the one hand that wouldn't be 100% right because according to
> ANSI C !(0) is just != 0 but no one says it is 1.

I believe you are wrong here.

!!x is common idiom using to turn anything into 0/1, used all over kernel.
									Pavel
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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