From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753220Ab3LMTRs (ORCPT ); Fri, 13 Dec 2013 14:17:48 -0500 Received: from mail-pa0-f45.google.com ([209.85.220.45]:61643 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751602Ab3LMTRr convert rfc822-to-8bit (ORCPT ); Fri, 13 Dec 2013 14:17:47 -0500 MIME-Version: 1.0 In-Reply-To: References: <20131213145657.265414969@infradead.org> <20131213150640.846368594@infradead.org> Date: Fri, 13 Dec 2013 20:17:46 +0100 X-Google-Sender-Auth: 9CZV-aObsg1zUPk2auzP4vsKlFw Message-ID: Subject: Fwd: [PATCH 3/4] arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h From: Geert Uytterhoeven To: "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Woops, misspelling of kernel.org in the original email... ---------- Forwarded message ---------- From: Geert Uytterhoeven Date: Fri, Dec 13, 2013 at 8:16 PM Subject: Re: [PATCH 3/4] arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h To: Peter Zijlstra Cc: Linux-Arch , linux-kernel@vger.kerne.org, Paul McKenney , Linus Torvalds , Victor Kaplansky , Oleg Nesterov , Anton Blanchard , Benjamin Herrenschmidt , Frédéric Weisbecker , Mathieu Desnoyers , Michael Ellerman , Michael Neuling , Russell King , Martin Schwidefsky , Heiko Carstens , Tony Luck Hi Peter, On Fri, Dec 13, 2013 at 3:57 PM, Peter Zijlstra wrote: > There are a few architectures (m32r, m68k) that could probably > do away with their barrier.h file entirely but are kept for now due to > their unconventional nop() implementation. m32r uses `__asm__ __volatile__ ("nop" : : )' instead of `asm volatile ("nop")'. Isn't the latter just a shorthand of the former? m68k has an additional `barrier()', which I think is unneeded. I looked at the asm output for drivers/block/ataflop.c and drivers/video/macfb.c, with and without the barrier. For ataflop, there were no differences. For macfb, removing the barrier allowed the compiler to keep the base addresses of the MMIO registers in registers, but there were no changes to the register accesses themselves. So IMHO both m32r and m68k can switch to the asm-generic version. I'm wondering whether we can just drop nop() from the in-kernel API? There are few users outside arch/: drivers/block/ataflop.c drivers/net/ethernet/amd/am79c961a.c drivers/tty/serial/crisv10.c drivers/video/macfb.c >>From a quick glance, all of them (ab)use nop() instead of one of the other primitives. For the macfb case, it seems to be due to missing ordering inside the nubus_*() I/O accessors. 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 -- 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