linux-kernel - Re: [PATCH] gpio: pxa: fix bug when get gpio value

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Date:	Wed, 15 Jan 2014 08:55:35 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Gerhard Sittig <gsi@...x.de>
Cc:	Neil Zhang <zhangwm@...vell.com>,
	Alexandre Courbot <gnurou@...il.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: pxa: fix bug when get gpio value

On Thu, Jan 9, 2014 at 11:46 AM, Gerhard Sittig <gsi@...x.de> wrote:

> Here is why I'm asking:  Is there a need from GPIO get_value()
> routines to return normalized values,

That totally depends.

All drivers calling gpio[d]_get_value() will be returned the
value directly from the driver without any clamping to [0,1] in
gpiolib. These are 496 occurences in the kernel, you'd have
to check them all to see if they expect this or not.

Hm. Maybe we should clamp it in gpiolib...

> and if so should not more
> drivers receive an update?

Probably. But on my part I want that more as a code
readability and maintenance hygiene thing, it gives a clear
sign that the driver author think about details.

(Possibly it gives the compiler a chance to optimize stuff
also, I don't quite know that.)

> If the GPIO subsystem's API wants to guarantee values of 0 and 1
> (which I think it doesn't), then I feel the adjustment should be
> done in the gpio_get_value() routines (in all its public
> variants, or a common routine which all of them pass through),
> and certainly not in individual chip drivers.

One does not exclude the other.

Yours,
Linus Walleij
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