From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754616AbbBTTVA (ORCPT ); Fri, 20 Feb 2015 14:21:00 -0500 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:53154 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752384AbbBTTU7 (ORCPT ); Fri, 20 Feb 2015 14:20:59 -0500 Date: Fri, 20 Feb 2015 19:20:43 +0000 From: Russell King - ARM Linux To: Mike Turquette Cc: Sascha Hauer , Tomi Valkeinen , stefan.wahren@i2se.com, devicetree@vger.kernel.org, sboyd@codeaurora.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, a.hajda@samsung.com, kernel@pengutronix.de, andy.yan@rock-chips.com, Liu Ying , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH RFC v9 01/20] clk: divider: Correct parent clk round rate if no bestdiv is normally found Message-ID: <20150220192043.GM8656@n2100.arm.linux.org.uk> References: <1423720903-24806-2-git-send-email-Ying.Liu@freescale.com> <20150212093356.GR12209@pengutronix.de> <20150212103944.GA1290@victor> <20150212122405.GW12209@pengutronix.de> <20150212125646.GT8656@n2100.arm.linux.org.uk> <20150212134131.GX12209@pengutronix.de> <54DE0BB8.7070004@ti.com> <20150213185713.GA12209@pengutronix.de> <20150216112724.GN8656@n2100.arm.linux.org.uk> <20150220191306.421.58746@quantum> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150220191306.421.58746@quantum> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 20, 2015 at 11:13:06AM -0800, Mike Turquette wrote: > Quoting Russell King - ARM Linux (2015-02-16 03:27:24) > > On Fri, Feb 13, 2015 at 07:57:13PM +0100, Sascha Hauer wrote: > > > I agree that it's a bit odd, but I think it has to be like this. > > > Consider that you request a rate of 100Hz, but the clock can only > > > produce 99.5Hz, so due to rounding clk_round_rate() returns 99Hz. > > > Now when you request 99Hz from clk_set_rate() the 99.5Hz value > > > can't be used because it's too high. > > > > Math rounding rules normally state that anything of .5 and greater > > should be rounded up, not rounded down. So, for 99.5Hz, you really > > ought to be returning 100Hz, not 99Hz. > > > > However, you do have a point for 99.4Hz, which would be returned as > > 99Hz, and when set, it would result in something which isn't 99.4Hz. > > More practically, this again raises the issue of whether or not unsigned > long rate should be in millihertz or something other than hertz. You still get the same issue if it's millihertz. Take 10 2/3rds Hz. Is 10.666 Hz less than 10 2/3rds Hz? -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net.