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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 0E3DFC4360F for ; Wed, 3 Apr 2019 15:14:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D9A3A2075E for ; Wed, 3 Apr 2019 15:14:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725990AbfDCPOX (ORCPT ); Wed, 3 Apr 2019 11:14:23 -0400 Received: from mailoutvs38.siol.net ([185.57.226.229]:52284 "EHLO mail.siol.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726099AbfDCPOT (ORCPT ); Wed, 3 Apr 2019 11:14:19 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.siol.net (Postfix) with ESMTP id 29BA55229E9; Wed, 3 Apr 2019 17:14:17 +0200 (CEST) X-Virus-Scanned: amavisd-new at psrvmta09.zcs-production.pri Received: from mail.siol.net ([127.0.0.1]) by localhost (psrvmta09.zcs-production.pri [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id z3kRh_h6lRjd; Wed, 3 Apr 2019 17:14:16 +0200 (CEST) Received: from mail.siol.net (localhost [127.0.0.1]) by mail.siol.net (Postfix) with ESMTPS id E058B5229DF; Wed, 3 Apr 2019 17:14:16 +0200 (CEST) Received: from localhost.localdomain (cpe-86-58-52-202.static.triera.net [86.58.52.202]) (Authenticated sender: 031275009) by mail.siol.net (Postfix) with ESMTPSA id 8C9595229E9; Wed, 3 Apr 2019 17:14:14 +0200 (CEST) From: Jernej Skrabec To: maxime.ripard@bootlin.com, wens@csie.org Cc: mturquette@baylibre.com, sboyd@kernel.org, linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, jernej.skrabec@siol.net Subject: [PATCH v2 2/2] clk: sunxi-ng: nkmp: Explain why zero width check is needed Date: Wed, 3 Apr 2019 17:14:04 +0200 Message-Id: <20190403151404.26542-3-jernej.skrabec@siol.net> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190403151404.26542-1-jernej.skrabec@siol.net> References: <20190403151404.26542-1-jernej.skrabec@siol.net> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: linux-clk-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-clk@vger.kernel.org Add an explanation why zero width check is needed when generating factor mask using GENMASK() macro. Signed-off-by: Jernej Skrabec --- drivers/clk/sunxi-ng/ccu_nkmp.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/clk/sunxi-ng/ccu_nkmp.c b/drivers/clk/sunxi-ng/ccu_n= kmp.c index 69dfc6de1c4e..cbcdf664f336 100644 --- a/drivers/clk/sunxi-ng/ccu_nkmp.c +++ b/drivers/clk/sunxi-ng/ccu_nkmp.c @@ -186,6 +186,12 @@ static int ccu_nkmp_set_rate(struct clk_hw *hw, unsi= gned long rate, =20 ccu_nkmp_find_best(parent_rate, rate, &_nkmp); =20 + /* + * If width is 0, GENMASK() macro may not generate expected mask (0) + * as it falls under undefined behaviour by C standard due to shifts + * which are equal or greater than width of left operand. This can + * be easily avoided by explicitly checking if width is 0. + */ if (nkmp->n.width) n_mask =3D GENMASK(nkmp->n.width + nkmp->n.shift - 1, nkmp->n.shift); --=20 2.21.0