Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0297BC04EBD for ; Tue, 16 Oct 2018 11:24:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C46C820881 for ; Tue, 16 Oct 2018 11:24:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C46C820881 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-wireless-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726977AbeJPTOa (ORCPT ); Tue, 16 Oct 2018 15:14:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44734 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726595AbeJPTOa (ORCPT ); Tue, 16 Oct 2018 15:14:30 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 17E64C05D40B; Tue, 16 Oct 2018 11:24:32 +0000 (UTC) Received: from localhost (unknown [10.43.2.63]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9DFA45D9C8; Tue, 16 Oct 2018 11:24:31 +0000 (UTC) Date: Tue, 16 Oct 2018 13:21:03 +0200 From: Stanislaw Gruszka To: Felix Fietkau Cc: Tom Psyborg , linux-wireless@vger.kernel.org, Daniel Golle , Mathias Kresin Subject: Re: [PATCH v4 4/8] rt2800: fix registers init for MT7620 Message-ID: <20181016112102.GC2621@redhat.com> References: <1539334591-9965-5-git-send-email-sgruszka@redhat.com> <20181012113656.GB2118@redhat.com> <20181012120329.GD2118@redhat.com> <20181012122630.GB2668@redhat.com> <20181016080922.GB4158@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 16 Oct 2018 11:24:32 +0000 (UTC) Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Tue, Oct 16, 2018 at 01:19:52PM +0200, Felix Fietkau wrote: > > I have no idea how this could be related. But I think I found > > somewhat reasonable explenation where the problem is. > > I think below code : > > > > if (a || b || c) { > > CODE1(); > > } else if (c) { > > CODE2(); > > } > > > > can not be deterministic and can be compiled differently depending > > on compiler version and used options. Sometimes it could result > > in this > > > > if (a || b || c) { > > CODE1(); > > } > > > > and sometimes in this: > > > > if (a || b) { > > CODE1(); > > } else if (c) { > > CODE2(); > > } > > > > So that would explain the problems you see. And indeed patch > > could cause regression on systems where second variant of > > initalizing RT6352 registers was used. > I don't see how that can be non-deterministic at all. The 'else if' part > can only be hit if the first if did not match. I meant non-deterministic during compilation process, when compiler do or do not some optimizations or if compiler version differs. Regards Stanislaw