Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933035Ab3HGSzW (ORCPT ); Wed, 7 Aug 2013 14:55:22 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:33824 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756335Ab3HGSzS (ORCPT ); Wed, 7 Aug 2013 14:55:18 -0400 Message-ID: <52029811.9080704@wwwdotorg.org> Date: Wed, 07 Aug 2013 12:55:13 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Viresh Kumar CC: rjw@sisk.pl, swarren@nvidia.com, linaro-kernel@lists.linaro.org, patches@linaro.org, cpufreq@vger.kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, mturquette@linaro.org, linux-arm-kernel@lists.infradead.org, "devicetree@vger.kernel.org" , Ian Campbell , Mark Rutland , Pawel Moll , Rob Herring Subject: Re: [PATCH 2/6] ARM: Tegra: Add CPU's OPPs for using cpufreq-cpu0 driver References: <52028719.8070908@wwwdotorg.org> In-Reply-To: X-Enigmail-Version: 1.4.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2471 Lines: 57 On 08/07/2013 12:06 PM, Viresh Kumar wrote: > On 7 August 2013 23:12, Stephen Warren wrote: >> On 08/07/2013 08:46 AM, Viresh Kumar wrote: >>> cpufreq-cpu0 driver needs OPPs to be present in DT which can be probed by it to >>> get frequency table. This patch adds OPPs and clock-latency to tegra cpu0 node >>> for multiple SoCs. >>> >>> Voltage levels aren't used until now for tegra and so a flat value which would >>> eventually be ignored is used to represent voltage. >> >> This patch is problematic w.r.t. DT being an ABI. > > :( > >> We can certainly add new optional properties to a DT binding that enable >> new features. However, a new version of a binding can't require new >> properties to exist that didn't before, since that means that old DTs >> won't work with new kernels that require the new properties. > > To be honest I didn't get it completely. You meant operating-points > wasn't present before? Its here: > > Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt > Documentation/devicetree/bindings/power/opp.txt > > Or you meant, Tegra never required voltage levels and we are getting > them in here. The current Tegra *.dts files do not contain this property. The current Tegra *.dts files must continue to work without modification in future kernels. >> As such, I believe we do need some Tegra-specific piece of code that >> defines these OPP tables in the kernel, so that the operating-points >> property is not needed. > > Generic cpufreq driver depends on OPP library and so somebody has > to provide them. Now you can do it by calling opp_add() for each OPP > you have or otherwise. Sure. That's what the Tegra-specific cpufreq driver should do. It should be the top-level cpufreq driver. If parts of the code can be implemented by library functions or a core parameterizable driver, then presumably the Tegra driver would simply exist to provide those parameters and/or callback functions to the generic driver. > Btw, you must have some specific voltage level for each freq, we can > get them here.. Yes, I'm sure we do, but I have no idea what they are:-( It may even be board-specific or SoC-SKU-specific. I think we should defer this aspect for now. -- 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/