From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752307AbcAFOc1 (ORCPT ); Wed, 6 Jan 2016 09:32:27 -0500 Received: from casper.infradead.org ([85.118.1.10]:47137 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751930AbcAFOcY (ORCPT ); Wed, 6 Jan 2016 09:32:24 -0500 Date: Wed, 6 Jan 2016 15:32:18 +0100 From: Peter Zijlstra To: "Michael S. Tsirkin" Cc: Rich Felker , linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, Rob Landley , Jeff Dionne , Yoshinori Sato Subject: Re: [PATCH v2 31/32] sh: support a 2-byte smp_store_mb Message-ID: <20160106143218.GV6344@twins.programming.kicks-ass.net> References: <1451572003-2440-1-git-send-email-mst@redhat.com> <1451572003-2440-32-git-send-email-mst@redhat.com> <20160105232735.GC238@brightrain.aerifal.cx> <20160106131321-mutt-send-email-mst@redhat.com> <20160106114023.GU6344@twins.programming.kicks-ass.net> <20160106134301-mutt-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160106134301-mutt-send-email-mst@redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 06, 2016 at 01:52:17PM +0200, Michael S. Tsirkin wrote: > > > Peter, what do you think? How about I leave this patch as is for now? > > > > No, and I object to removing the single byte implementation too. Either > > remove the full arch or fix xchg() to conform. xchg() should work on all > > native word sizes, for SH that would be 1,2 and 4 bytes. > > Rick, maybe you could explain how is current 1 byte xchg on llsc wrong? It doesn't seem to preserve the 3 other bytes in the word. > It does use 4 byte accesses but IIUC that is all that exists on > this architecture. Right, that's not a problem, look at arch/alpha/include/asm/xchg.h for example. A store to another portion of the word should make the store-conditional fail and we'll retry the loop. The short versions should however preserve the other bytes in the word. SH's cmpxchg() is equally incomplete and does not provide 1 and 2 byte versions. In any case, I'm all for rm -rf arch/sh/, one less arch to worry about is always good, but ISTR some people wanting to resurrect SH: http://old.lwn.net/Articles/647636/ Rob, Jeff, Sato-san, might I suggest you send a MAINTAINERS patch and take up an active interest in SH lest someone 'accidentally' nukes it?