From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Subject: Re: [PATCH 14/54] gpio: pch: Be sure to clamp return value Date: Mon, 4 Jan 2016 10:41:41 +0100 Message-ID: <20160104104141.14cf44d9@endymion.delvare> References: <1450794054-22948-1-git-send-email-linus.walleij@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from mx2.suse.de ([195.135.220.15]:46881 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751521AbcADJlo (ORCPT ); Mon, 4 Jan 2016 04:41:44 -0500 In-Reply-To: <1450794054-22948-1-git-send-email-linus.walleij@linaro.org> Sender: linux-gpio-owner@vger.kernel.org List-Id: linux-gpio@vger.kernel.org To: Linus Walleij Cc: linux-gpio@vger.kernel.org, Thierry Reding , Daniel Krueger Hi Linus, On Tue, 22 Dec 2015 15:20:54 +0100, Linus Walleij wrote: > As we want gpio_chip .get() calls to be able to return negative > error codes and propagate to drivers, we need to go over all > drivers and make sure their return values are clamped to [0,1]. > We do this by using the ret = !!(val) design pattern. > > Cc: Thierry Reding > Cc: Daniel Krueger > Cc: Jean Delvare > Signed-off-by: Linus Walleij > --- > drivers/gpio/gpio-pch.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpio/gpio-pch.c b/drivers/gpio/gpio-pch.c > index af0715f8524b..8c45b74dcf21 100644 > --- a/drivers/gpio/gpio-pch.c > +++ b/drivers/gpio/gpio-pch.c > @@ -127,7 +127,7 @@ static int pch_gpio_get(struct gpio_chip *gpio, unsigned nr) > { > struct pch_gpio *chip = container_of(gpio, struct pch_gpio, gpio); > > - return ioread32(&chip->reg->pi) & (1 << nr); > + return !!(ioread32(&chip->reg->pi) & (1 << nr)); > } > > static int pch_gpio_direction_output(struct gpio_chip *gpio, unsigned nr, I would prefer: return (ioread32(&chip->reg->pi) >> nr) & 1; which is faster for the same result. At x86 assembly level, your approach requires 5 CPU instructions (mov, shl, test, setne and movzbl), mine only 2 CPU instructions (shr and and.) -- Jean Delvare SUSE L3 Support