Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932288AbbBLMYS (ORCPT ); Thu, 12 Feb 2015 07:24:18 -0500 Received: from metis.ext.pengutronix.de ([92.198.50.35]:34560 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932216AbbBLMYR (ORCPT ); Thu, 12 Feb 2015 07:24:17 -0500 Date: Thu, 12 Feb 2015 13:24:05 +0100 From: Sascha Hauer To: Liu Ying Cc: dri-devel@lists.freedesktop.org, stefan.wahren@i2se.com, devicetree@vger.kernel.org, linux@arm.linux.org.uk, kernel@pengutronix.de, sboyd@codeaurora.org, linux-kernel@vger.kernel.org, a.hajda@samsung.com, andy.yan@rock-chips.com, mturquette@linaro.org, linux-arm-kernel@lists.infradead.org, Tomi Valkeinen Subject: Re: [PATCH RFC v9 01/20] clk: divider: Correct parent clk round rate if no bestdiv is normally found Message-ID: <20150212122405.GW12209@pengutronix.de> References: <1423720903-24806-1-git-send-email-Ying.Liu@freescale.com> <1423720903-24806-2-git-send-email-Ying.Liu@freescale.com> <20150212093356.GR12209@pengutronix.de> <20150212103944.GA1290@victor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150212103944.GA1290@victor> X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Uptime: 13:09:52 up 119 days, 23:23, 161 users, load average: 0.00, 0.01, 0.05 User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3679 Lines: 69 On Thu, Feb 12, 2015 at 06:39:45PM +0800, Liu Ying wrote: > On Thu, Feb 12, 2015 at 10:33:56AM +0100, Sascha Hauer wrote: > > On Thu, Feb 12, 2015 at 02:01:24PM +0800, Liu Ying wrote: > > > If no best divider is normally found, we will try to use the maximum divider. > > > We should not set the parent clock rate to be 1Hz by force for being rounded. > > > Instead, we should take the maximum divider as a base and calculate a correct > > > parent clock rate for being rounded. > > > > Please add an explanation why you think the current code is wrong and > > what this actually fixes, maybe an example? > > The MIPI DSI panel's pixel clock rate is 26.4MHz and it's derived from PLL5 on > the MX6DL SabreSD board. > > These are the clock tree summaries with or without the patch applied: > 1) With the patch applied: > pll5_bypass_src 1 1 24000000 0 0 > pll5 1 1 844800048 0 0 > pll5_bypass 1 1 844800048 0 0 > pll5_video 1 1 844800048 0 0 > pll5_post_div 1 1 211200012 0 0 > pll5_video_div 1 1 211200012 0 0 > ipu1_di0_pre_sel 1 1 211200012 0 0 > ipu1_di0_pre 1 1 26400002 0 0 > ipu1_di0_sel 1 1 26400002 0 0 > ipu1_di0 1 1 26400002 0 0 > > 2) Without the patch applied: > pll5_bypass_src 1 1 24000000 0 0 > pll5 1 1 648000000 0 0 > pll5_bypass 1 1 648000000 0 0 > pll5_video 1 1 648000000 0 0 > pll5_post_div 1 1 162000000 0 0 > pll5_video_div 1 1 40500000 0 0 > ipu1_di0_pre_sel 1 1 40500000 0 0 > ipu1_di0_pre 1 1 20250000 0 0 > ipu1_di0_sel 1 1 20250000 0 0 > ipu1_di0 1 1 20250000 0 0 This seems to be broken since: | commit b11d282dbea27db1788893115dfca8a7856bf205 | Author: Tomi Valkeinen | Date: Thu Feb 13 12:03:59 2014 +0200 | | clk: divider: fix rate calculation for fractional rates This patch fixed a case when clk_set_rate(clk_round_rate(rate)) resulted in a lower frequency than clk_round_rate(rate) returned. Since then the MULT_ROUND_UP in clk_divider_bestdiv() is inconsistent to the rest of the divider. Maybe this should be a simple rate * i now, but I'm unsure what side effects this has. I think your patch only fixes the behaviour in your case by accident, it's not a correct fix for this issue. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/