Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754850AbbFBMMm (ORCPT ); Tue, 2 Jun 2015 08:12:42 -0400 Received: from mail-wi0-f179.google.com ([209.85.212.179]:34331 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753246AbbFBMMe (ORCPT ); Tue, 2 Jun 2015 08:12:34 -0400 Date: Tue, 2 Jun 2015 14:12:29 +0200 From: Luc Van Oostenryck To: Paul Burton Cc: Leonid Yegoshin , linux-mips@linux-mips.org, benh@kernel.crashing.org, will.deacon@arm.com, linux-kernel@vger.kernel.org, ralf@linux-mips.org, markos.chandras@imgtec.com, macro@linux-mips.org, Steven.Hill@imgtec.com, alexander.h.duyck@redhat.com, davem@davemloft.net Subject: Re: [PATCH 1/3] MIPS: R6: Use lightweight SYNC instruction in smp_* memory barriers Message-ID: <20150602121227.GA1474@macpro.local> References: <20150602000818.6668.76632.stgit@ubuntu-yegoshin> <20150602000934.6668.43645.stgit@ubuntu-yegoshin> <20150602100835.GG24014@NP-P-BURTON> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150602100835.GG24014@NP-P-BURTON> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2027 Lines: 48 On Tue, Jun 02, 2015 at 11:08:35AM +0100, Paul Burton wrote: > Hi Leonid, > > > + > > + If that instructions are not implemented in processor then it is > > + converted to generic "SYNC 0". > > I think this would read better as something like: > > If a processor does not implement the lightweight sync operations then > the architecture requires that they interpret the corresponding sync > instructions as the typical heavyweight "sync 0". Therefore this > should be safe to enable on all CPUs implementing release 2 or > later of the MIPS architecture. > Is it really the case for release 2? I'm asking because recently I needed to do something similar and I couldn't find this garantee in the revision 2.00 of the manual. May it's just poorly formulated but here is what I find in it: - "The stype values 1-31 are reserved for future extensions to the architecture." (ok) - "A value of zero will always be defined such that it performs all defined synchronization operations." (ok) - "Non-zero values may be defined to remove some synchronization operations." (ok, certainly if we understand the word "weaker" instead of "remove") - "As such, software should never use a non-zero value of the stype field, as this may inadvertently cause future failures if non-zero values remove synchronization operations." (Mmmm, ok but ...) Nowhere is there something close to what is found in the revision 5.0 or later: "If an implementation does not use one of these non-zero values to define a different synchronization behavior, then that non-zero value of stype must act the same as stype zero completion barrier." The wording may have changed since revision 2.8 but I don't have access to the corresponding manual. Luc Van Oostenryck -- 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/