From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757926AbdCUPEt (ORCPT ); Tue, 21 Mar 2017 11:04:49 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:15795 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757163AbdCUPEr (ORCPT ); Tue, 21 Mar 2017 11:04:47 -0400 Subject: Re: [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation To: Segher Boessenkool References: <20170309094206.A832167992@localhost.localdomain> <87a88tle0y.fsf@concordia.ellerman.id.au> <534d8795-ce21-9af6-498d-22597213a3a2@c-s.fr> <20170310130630.GH31469@gate.crashing.org> <906c025b-47d0-f906-2613-291f350bd48d@c-s.fr> <20170310143241.GJ31469@gate.crashing.org> <777e903f-b816-5efa-2ece-e4e16fab27c6@c-s.fr> <20170310154139.GM31469@gate.crashing.org> Cc: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Scott Wood , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org From: Christophe LEROY Message-ID: Date: Tue, 21 Mar 2017 16:04:40 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170310154139.GM31469@gate.crashing.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 10/03/2017 à 16:41, Segher Boessenkool a écrit : > On Fri, Mar 10, 2017 at 03:41:23PM +0100, Christophe LEROY wrote: >>>>>> gpio_get() and gpio_set() are used extensively by some GPIO based >>>>>> drivers like SPI, NAND, so it may be worth it as it doesn't impair >>>>>> readability (if anyone prefers, we could write (1 << 31) >> i instead >>>>>> of 0x80000000 >> i ) >>>>> 1 << 31 is undefined behaviour, of course. >>>> Shall it be 1U << 31 ? >>> Sure, that works. "1 << (31 - i)" is most readable (but it doesn't yet >>> generate the code you want). >> Euh .... I'm a bit lost. Do you mean the form we have today is the >> driver is wrong ? > Heh, yes. But is't okay with GCC, so don't worry about it. > > The point is that "0x80000000 >> i" is less readable. > > FYI, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80131 Christophe