From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Turquette Subject: Re: [PATCH RFC v9 01/20] clk: divider: Correct parent clk round rate if no bestdiv is normally found Date: Fri, 20 Feb 2015 11:42:27 -0800 Message-ID: <20150220194227.421.44526@quantum> References: <1423720903-24806-2-git-send-email-Ying.Liu@freescale.com> <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> <20150220192043.GM8656@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150220192043.GM8656@n2100.arm.linux.org.uk> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Russell King - ARM Linux Cc: stefan.wahren@i2se.com, devicetree@vger.kernel.org, Sascha Hauer , sboyd@codeaurora.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, a.hajda@samsung.com, Tomi Valkeinen , kernel@pengutronix.de, andy.yan@rock-chips.com, Liu Ying , linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org Quoting Russell King - ARM Linux (2015-02-20 11:20:43) > 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? Millihertz won't solve rounding problems, I agree. But we currently do not support any fractional rates and we should. Regards, Mike > > -- > FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up > according to speedtest.net.