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

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Date:	Wed, 5 Mar 2014 11:22:30 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Joe Perches <joe@...ches.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, Mar 5, 2014 at 11:19 AM, Joe Perches <joe@...ches.com> wrote:
> 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.

Ok, you are obviously correct here. Linus, what do you think?
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