From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from service87.mimecast.com ([91.220.42.44]:56661 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752771Ab3HVQ1m convert rfc822-to-8bit (ORCPT ); Thu, 22 Aug 2013 12:27:42 -0400 Message-ID: <52163C1A.4040707@arm.com> Date: Thu, 22 Aug 2013 17:28:10 +0100 From: Sudeep KarkadaNagesha MIME-Version: 1.0 Subject: Re: [RFC PATCH 1/2] PM / OPP: add support to specify phandle of another node for OPP References: <51F93AFB.1030104@ti.com> <20130801135422.GA8095@e106331-lin.cambridge.arm.com> <51FA8BE2.9000309@ti.com> <20130802131541.GN2884@e106331-lin.cambridge.arm.com> <20130806134534.GB6603@kahuna> <20130807161722.GJ28558@e106331-lin.cambridge.arm.com> <52133E26.1000801@arm.com> <521543AC.4020709@wwwdotorg.org> <20130822115957.GC9799@e106331-lin.cambridge.arm.com> <52162EFA.2070108@arm.com> <20130822155000.GF23152@e106331-lin.cambridge.arm.com> In-Reply-To: <20130822155000.GF23152@e106331-lin.cambridge.arm.com> Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Sender: devicetree-owner@vger.kernel.org To: Mark Rutland Cc: Sudeep KarkadaNagesha , Stephen Warren , Nishanth Menon , "cpufreq@vger.kernel.org" , "linux-pm@vger.kernel.org" , "devicetree@vger.kernel.org" , "rob.herring@calxeda.com" , Pawel Moll , "Rafael J. Wysocki" List-ID: On 22/08/13 16:50, Mark Rutland wrote: > On Thu, Aug 22, 2013 at 04:32:10PM +0100, Sudeep KarkadaNagesha wrote: >> On 22/08/13 12:59, Mark Rutland wrote: >>> On Wed, Aug 21, 2013 at 11:48:12PM +0100, Stephen Warren wrote: [...] >>>> >>>> I'd suggest/bike-shed that operating-points-device is not the correct >>>> property name; it somehow implies that the other device actively defines >>>> the OPPs for this device, rather than just happening to have the same >>>> OPPs. Perhaps "operating-points-identical-to"? >>>> >>> >>> I'd rather not have properties that point elsewhere and say "treat me >>> the same as this node". I'd rather we have common properties as >>> described above. >>> >> Agreed, but for platforms with multiple CPU clusters, since we have only >> one /cpus node, we ned to have table node which is arguable if node has >> represent a device(as mentioned above) > > I agree that this seems wasteful of space, but I really don't think that > pointing at another device you want the OPPs of is the best way of > describing the linkage, and I suspect we'll get all sorts of stupid bugs > resulting from that style of binding. > > Consider the following (properties trimmed for brevity): > > cpus { > cpu0: cpu@0 { > operating-points-identical-to = <&cpu1>; > }; > cpu1: cpu@1 { > operating-points = <0 100>, > <23 47>, > <62 970>; > } > }; > > If we boot a UP kernel on the above, I assume we won't read the info for > cpu1, and thus we won't get operating points info for cpu0. Worse, what > if cpu1 has status="disabled"? Does that make its OPP table invalid? > What if the bootloader drops cpu1? > Another question :), does status property dictate the validity of the other properties in the node(not specific to above example, in general)? But I agree that this indirect linkage is broken as boot-loaders can drop the cpu node holding OPP. IMO fallback method would be reasonable(and much cleaner compared to a separate node) if it can even accommodate multiple cpu clusters. > I really don't like indirecting linkage to a property through an > arbitrary node, simply because it happened to have the same property. It > creates an artificial depdendency that will lead to problems. > I totally agree on this. Regards, Sudeep