From mboxrd@z Thu Jan 1 00:00:00 1970 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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 D8CADC2D0C2 for ; Fri, 3 Jan 2020 14:59:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9FF9121734 for ; Fri, 3 Jan 2020 14:59:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727920AbgACO7Q (ORCPT ); Fri, 3 Jan 2020 09:59:16 -0500 Received: from mx2.suse.de ([195.135.220.15]:39180 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725890AbgACO7P (ORCPT ); Fri, 3 Jan 2020 09:59:15 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id B5235ACCA; Fri, 3 Jan 2020 14:59:13 +0000 (UTC) Received: by unicorn.suse.cz (Postfix, from userid 1000) id B8231E0473; Fri, 3 Jan 2020 15:59:11 +0100 (CET) Date: Fri, 3 Jan 2020 15:59:11 +0100 From: Michal Kubecek To: netdev@vger.kernel.org Cc: Matthew Wilcox , yu kuai , klassert@kernel.org, davem@davemloft.net, hkallweit1@gmail.com, jakub.kicinski@netronome.com, hslester96@gmail.com, mst@redhat.com, yang.wei9@zte.com.cn, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, zhengbin13@huawei.com Subject: Re: [PATCH] net: 3com: 3c59x: remove set but not used variable 'mii_reg1' Message-ID: <20200103145911.GA22387@unicorn.suse.cz> References: <20200103121907.5769-1-yukuai3@huawei.com> <20200103144623.GI6788@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200103144623.GI6788@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 03, 2020 at 06:46:23AM -0800, Matthew Wilcox wrote: > On Fri, Jan 03, 2020 at 08:19:07PM +0800, yu kuai wrote: > > Fixes gcc '-Wunused-but-set-variable' warning: > > > > drivers/net/ethernet/3com/3c59x.c: In function ‘vortex_up’: > > drivers/net/ethernet/3com/3c59x.c:1551:9: warning: variable > > ‘mii_reg1’ set but not used [-Wunused-but-set-variable] > > > > It is never used, and so can be removed. > ... > > if (dev->if_port == XCVR_MII || dev->if_port == XCVR_NWAY) { > > - mii_reg1 = mdio_read(dev, vp->phys[0], MII_BMSR); > > mii_reg5 = mdio_read(dev, vp->phys[0], MII_LPA); > > I know nothing about the MII interface, but in general this is not > a safe thing to do. You're removing a read from a device register. > Register reads can have side effects. I'm actually quite surprised > that GCC emits this warning, since there should be some kind of > volatile cast in mdio_read() to let GCC know that something unusual > is going on here. Removing the call may be wrong (and certainly isn't obviously correct) but the warning makes sense, IMHO: if the return value is not used anywhere, there is no point assigning it to a variable. Michal Kubecek