Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752122AbbKPI2N (ORCPT ); Mon, 16 Nov 2015 03:28:13 -0500 Received: from mail-ob0-f176.google.com ([209.85.214.176]:33667 "EHLO mail-ob0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751928AbbKPI2K (ORCPT ); Mon, 16 Nov 2015 03:28:10 -0500 MIME-Version: 1.0 In-Reply-To: <56498D0A.3070000@synopsys.com> References: <5613F3DE.4010406@suse.cz> <1444165543-2209-1-git-send-email-linux@rasmusvillemoes.dk> <56498D0A.3070000@synopsys.com> Date: Mon, 16 Nov 2015 09:28:09 +0100 X-Google-Sender-Auth: Ki65gMYVUTnOhHszU_WoGCM_ByU Message-ID: Subject: Re: using IS_ENABLED(CONFIG_xyz) effectively From: Geert Uytterhoeven To: Vineet Gupta Cc: Rasmus Villemoes , Paul Gortmaker , Ingo Molnar , Andrew Morton , Thomas Gleixner , "H. Peter Anvin" , Michal Marek , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , arcml Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1884 Lines: 51 Hi Vineet, On Mon, Nov 16, 2015 at 9:00 AM, Vineet Gupta wrote: > I've been using IS_ENABLED for some time and once in a while run into an issue > which prevents seamless use. Hence posing this question to experts in the area. > > C macro processor evaluates the ensuing control block even if IS_ENABLED evaluates > to false. This requires dummy #defines or worse still removing usage of IS_ENABLED > altogether. > > e.g. In example below even for ARCOMPACT builds, we need the ARCV2 specific define > ARCV2_IRQ_DEF_PRIO. > > void arch_cpu_idle(void) > { > if (is_isa_arcompact()) { <---- IS_ENABLED(CONFIG_ISA_ARCOMPACT) > __asm__("sleep 0x3"); > } else { > const int arg = 0x10 | ARCV2_IRQ_DEF_PRIO; > __asm__("sleep 0x10"); > } > } > > One could argue that the interface needs to be cleanly defined to not have such > specific #defines in common code in first place. However sometime that becomes > just too tedious. > > Is there a way to get around by this ? Use #ifdef CONFIG_...? The advantage of IS_ENABLED() over #ifdef is that it allows compile-testing of the disabled code path. Of course it should only be compiled if it makes sense. And that's exactly what you're running into. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/