Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753492AbeADWom (ORCPT + 1 other); Thu, 4 Jan 2018 17:44:42 -0500 Received: from mail-io0-f194.google.com ([209.85.223.194]:45808 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752552AbeADWok (ORCPT ); Thu, 4 Jan 2018 17:44:40 -0500 X-Google-Smtp-Source: ACJfBote3bjiS+GJ2nexeDCVnnEfmIqqfV2ePiKmTiKWbsd08VDgaiSyFe+QBKGcp1CfpKGU3+//VdQZUrEFkBwlV3k= MIME-Version: 1.0 In-Reply-To: <20180104195650.vmbooz3pwjy77wt7@flea.lan> References: <20171226111227.4526-1-net147@gmail.com> <20171226111227.4526-2-net147@gmail.com> <20180104195650.vmbooz3pwjy77wt7@flea.lan> From: Jonathan Liu Date: Fri, 5 Jan 2018 09:44:39 +1100 Message-ID: Subject: Re: [PATCH v2 1/3] drm/sun4i: hdmi: Check for unset best_parent in sun4i_tmds_determine_rate To: Maxime Ripard Cc: David Airlie , Chen-Yu Tsai , linux-kernel , dri-devel , linux-arm-kernel , linux-sunxi Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: Hi Maxime, On 5 January 2018 at 06:56, Maxime Ripard wrote: > On Tue, Dec 26, 2017 at 10:12:25PM +1100, Jonathan Liu wrote: >> We should check if the best match has been set before comparing it. >> >> Fixes: 9c5681011a0c ("drm/sun4i: Add HDMI support") >> Signed-off-by: Jonathan Liu >> --- >> drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c >> index dc332ea56f6c..4d235e5ea31c 100644 >> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c >> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c >> @@ -102,7 +102,7 @@ static int sun4i_tmds_determine_rate(struct clk_hw *hw, >> goto out; >> } >> >> - if (abs(rate - rounded / i) < >> + if (!best_parent || abs(rate - rounded / i) < > > Why is that causing any issue? > > If best_parent is set to 0... > >> abs(rate - best_parent / best_div)) { > > ... the value returned here is going to be rate, which is going to be > higher than the first part of the comparison meaning ... > >> best_parent = rounded; > > ... that best_parent is going to be set there. Consider the following: rate = 83500000 rounded = ideal * 2 It is possible that if "rounded = clk_hw_round_rate(parent, ideal)" gives high enough values that the condition "abs(rate - rounded / i) < abs(rate - best_parent / best_div)" is never met. Then you can end up with: req->rate = 0 req->best_parent_rate = 0 req->best_parent_hw = ... Also, the sun4i_tmds_calc_divider function has a similar check. Regards, Jonathan