From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [RFC] cpufreq: Add "dvfs-method" binding to probe cpufreq drivers Date: Fri, 28 Nov 2014 12:01:42 +0530 Message-ID: References: <596a6d49f2b3e2837aa9a54a3e1249161d3c9265.1416991009.git.viresh.kumar@linaro.org> <5476071B.1060705@arm.com> <5476F4ED.6040206@arm.com> <547707C8.3080108@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: Received: from mail-ob0-f175.google.com ([209.85.214.175]:40924 "EHLO mail-ob0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750929AbaK1Gbn (ORCPT ); Fri, 28 Nov 2014 01:31:43 -0500 Received: by mail-ob0-f175.google.com with SMTP id wp4so4665195obc.34 for ; Thu, 27 Nov 2014 22:31:43 -0800 (PST) In-Reply-To: <547707C8.3080108@arm.com> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Sudeep Holla Cc: Rafael Wysocki , "rob.herring@linaro.org" , "linaro-kernel@lists.linaro.org" , "linux-pm@vger.kernel.org" , Nishanth Menon , Stephen Boyd , "devicetree@vger.kernel.org" , Santosh Shilimkar , Lorenzo Pieralisi , Arnd Bergmann , Mike Turquette , "grant.likely@linaro.org" , "kesavan.abhilash@gmail.com" , Catalin Marinas , "k.chander@samsung.com" , "olof@lixom.net" , "ta.omasab@gmail.com" On 27 November 2014 at 16:45, Sudeep Holla wrote: > It's the general understanding, I am not sure if it's specified anywhere > in the kernel Documentation, but I could find the below excerpts from [1]: > > "The compatibility rules say that new kernels must work with older > device trees. If changes are required, they should be put into new > properties; the old ones can then be deprecated but not removed. New > properties should be optional, so that device trees lacking those > properties continue to work. The device tree developers will provide a > set of guidelines for the creation of future-proof bindings." > > It's *exactly opposite* as DTs are considered as part of firmware that > gets shipped with the boards and any kernel should work with that DT if > it is compliance with the DT bindings(even old, as the DT bindings > should never get changed only gets extended) Okay, I was completely wrong. :) > No, you *must* :). That's backward compatibility. Just consider a simple > case where the bootloader is generating DT and we don't want to upgrade it. Now these are the options we have for existing platforms: - Update those platforms to check if DT has "compatible" string in CPU node. If yes, don't create a device as this will be created by cpufreq-dt. - Just remove the device creation from those paths if the Maintainers of those platforms want to cleanup their code, accepting the loss of backward compatibility.. -- viresh