From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH] bus: subsys: propagate errors from subsys interface's ->add_dev() Date: Fri, 31 Jul 2015 15:41:31 +0200 Message-ID: <1728127.lyUO7fLBpR@vostro.rjw.lan> References: <8139001.Q4eV8YG1Il@vostro.rjw.lan> <20150731060907.GO17794@linux> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: Received: from v094114.home.net.pl ([79.96.170.134]:62620 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750926AbbGaNOd (ORCPT ); Fri, 31 Jul 2015 09:14:33 -0400 In-Reply-To: <20150731060907.GO17794@linux> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Viresh Kumar Cc: Greg KH , linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, pi-cheng.chen@linaro.org On Friday, July 31, 2015 11:39:07 AM Viresh Kumar wrote: > On 30-07-15, 20:53, Rafael J. Wysocki wrote: > > Well, on ACPI systems we actually do probe CPU devices. We have a processor > > driver there that binds to CPU devices and the cpufreq driver is just a > > frontend to that. > > Hmm, maybe I need to look at that in detail.. > > > So question is what prevents DT-based systems from doing it analogously. > > Don't have an answer to it yet. > > > Now, even if you use a fake platform device for that (I'm sure there are > > reasons for doing that, but I'd very much like them to be explained), > > The other reason apart from the EPROBE_DEFER thing was to identify the > right driver for a platform. For multiplatform kernels, there can be > multiple cpufreq drivers present in the kernel and there was no other > way to identify the right driver platform wants to probe. > > > then > > all of the information on dependencies should already be available to the > > ->probe callback of that device's driver, so it can check them before > > registering the cpufreq interface, can't it? > > That's what we try to do today for cpufreq-dt, for example. But that > has to be done for every possible policy the system can have as all > might have separate resources to allocate. For cpufreq-dt, we do it > only for cpu0 today, and assume others will work as well if cpu0 can. > > The real deal is that we need a probe() per policy here, for which > init() fitted well :) > > > Essentially, what you're suggesting to do is something like: Make the ->probe > > of one device's driver register a subsys interface for a specific bus type > > and check what ->add_dev of that interface returns for each device on that > > bus and if that is -EPROBE_DEFER, return it as its own return value. Do you > > honestly think this is a good design? > > No. I don't really thing so. That's why I was asking for suggestions > to do it proper. Maybe processor driver is the way to look for, I will > investigate further on that. > > But until the time that is done, and I expect that to take some time, > can't we check the return value of ->add_dev()? As I said, either do it everywhere, or do it nowhere (in which case it can be void). Doing it in one place only is plain confusing and generally incorrect. Thanks, Rafael