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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AFA35C001DF for ; Tue, 25 Jul 2023 04:07:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230168AbjGYEHN (ORCPT ); Tue, 25 Jul 2023 00:07:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47750 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230128AbjGYEHK (ORCPT ); Tue, 25 Jul 2023 00:07:10 -0400 Received: from mail.nfschina.com (unknown [42.101.60.195]) by lindbergh.monkeyblade.net (Postfix) with SMTP id 7CA1FA3; Mon, 24 Jul 2023 21:07:08 -0700 (PDT) Received: from [172.30.11.106] (unknown [180.167.10.98]) by mail.nfschina.com (Maildata Gateway V2.8.8) with ESMTPSA id 2F9D46031EAE1; Tue, 25 Jul 2023 12:06:51 +0800 (CST) Message-ID: <352f7c10-3592-4a18-abdc-ab554a992d10@nfschina.com> Date: Tue, 25 Jul 2023 12:06:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [Intel-gfx] [PATCH v2] drm/i915/tv: avoid possible division by zero Content-Language: en-US To: Andi Shyti Cc: jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, tvrtko.ursulin@linux.intel.com, airlied@gmail.com, daniel@ffwll.ch, nathan@kernel.org, ndesaulniers@google.com, trix@redhat.com, andrzej.hajda@intel.com, intel-gfx@lists.freedesktop.org, llvm@lists.linux.dev, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, mripard@kernel.org X-MD-Sfrom: suhui@nfschina.com X-MD-SrcIP: 180.167.10.98 From: Su Hui In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/7/25 01:35, Andi Shyti wrote: > On Tue, Jul 18, 2023 at 09:32:17AM +0800, Su Hui wrote: >> Clang warning: drivers/gpu/drm/i915/display/intel_tv.c: >> line 991, column 22 Division by zero. >> Assuming tv_mode->oversample=1 and (!tv_mode->progressive)=1, >> then division by zero will happen. >> >> Fixes: 1bba5543e4fe ("drm/i915: Fix TV encoder clock computation") >> Signed-off-by: Su Hui >> --- >> drivers/gpu/drm/i915/display/intel_tv.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/i915/display/intel_tv.c b/drivers/gpu/drm/i915/display/intel_tv.c >> index 36b479b46b60..f59553f7c132 100644 >> --- a/drivers/gpu/drm/i915/display/intel_tv.c >> +++ b/drivers/gpu/drm/i915/display/intel_tv.c >> @@ -988,7 +988,7 @@ intel_tv_mode_to_mode(struct drm_display_mode *mode, >> const struct tv_mode *tv_mode, >> int clock) >> { >> - mode->clock = clock / (tv_mode->oversample >> !tv_mode->progressive); >> + mode->clock = clock / tv_mode->oversample << !tv_mode->progressive; > but this does not provide the same value. Try with: > > 8 / (2 >> 1) > > and > > 8 / 2 << 1 > > They are definitely different. > > The real check could be: > > if (!(tv_mode->oversample >> 1)) > return ... > > But first I would check if that's actually possible. Oh, I have a v3 patch, like this: -       mode->clock = clock / (tv_mode->oversample >> !tv_mode->progressive); +       mode->clock = clock; +       if (tv_mode->oversample >> !tv_mode->progressive) +               mode->clock /= tv_mode->oversample >> 1; But I'm not sure does it need to print some error messages or do some things  when "tv_mode->oversample << !tv_mode->progressive" is zero? If all right , I will send this v3 patch. Su Hui > Andi