linux-kernel - Re: [PATCH] gpio: clamp returned values to the boolean range

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Message-ID: <1393985959.3271.25.camel@joe-AO722>
Date:	Tue, 04 Mar 2014 18:19:19 -0800
From:	Joe Perches <joe@...ches.com>
To:	Alexandre Courbot <gnurou@...il.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <acourbot@...dia.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: clamp returned values to the boolean range

On Wed, 2014-03-05 at 11:14 +0900, Alexandre Courbot wrote:
> On Wed, Mar 5, 2014 at 11:04 AM, Joe Perches <joe@...ches.com> wrote:
> > On Wed, 2014-03-05 at 09:49 +0800, Linus Walleij wrote:
> >> On Wed, Feb 26, 2014 at 9:40 AM, Alexandre Courbot <acourbot@...dia.com> wrote:
> >>
> >> > Nothing prevents GPIO drivers from returning values outside the
> >> > boolean range, and as it turns out a few drivers are actually doing so.
> >> > These values were passed as-is to unsuspecting consumers and created
> >> > confusion.
> >> >
> >> > This patch makes the internal _gpiod_get_raw_value() function return a
> >> > bool, effectively clamping the GPIO value to the boolean range no
> >> > matter what the driver does.
> >>
> >> No, that will not be the semantic effect of this patch, bool is just
> >> another name for an int, maybe some static checkers will be able
> >> to use it however.
> >
> > No, a bool is not an int.
> >
> > It's really different.
> > include/linux/types.h:typedef _Bool                     bool;
> 
> It indeed seems that _Bool is an actual boolean type in C99. However I
> could not find in the C99 standard how ints are supposed to be
> converted to it.

6.3.1.2 Boolean type

When any scalar value is converted to _Bool, the result is 0 if the
value compares equal to 0; otherwise, the result is 1.

> So in the end it is probably safer to perform this
> change the way Linus suggested.

Not really.


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