From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752660AbbGaGJR (ORCPT ); Fri, 31 Jul 2015 02:09:17 -0400 Received: from mail-pd0-f181.google.com ([209.85.192.181]:33336 "EHLO mail-pd0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751701AbbGaGJN (ORCPT ); Fri, 31 Jul 2015 02:09:13 -0400 Date: Fri, 31 Jul 2015 11:39:07 +0530 From: Viresh Kumar To: "Rafael J. Wysocki" Cc: Greg KH , linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, pi-cheng.chen@linaro.org Subject: Re: [PATCH] bus: subsys: propagate errors from subsys interface's ->add_dev() Message-ID: <20150731060907.GO17794@linux> References: <2113628.vmLC8GdsGl@vostro.rjw.lan> <20150730034431.GH5100@linux> <8139001.Q4eV8YG1Il@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8139001.Q4eV8YG1Il@vostro.rjw.lan> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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()? -- viresh