From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, T_DKIMWL_WL_HIGH,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 42819C072B5 for ; Fri, 24 May 2019 05:52:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0478521841 for ; Fri, 24 May 2019 05:52:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558677142; bh=isQJuIhcuCBrs0hEM9Rq67SyZfcwBKSPB6Sk8DBiWws=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=PqnJDd2RbYFx7L5Y/jJaTAPn9VxcbuO+6Uux2QGAeV0DmSC4Zoyh6wBYAPewcC2Qg Cnz+i7v8l83i/HPsXz1RFK7GOy3BvLa47KuXvlfXwN50SLHUShuZcyxwNkbTqW7DDr AxaY6uAKmZCAQdYx7CXLN/dRDLNnA2eciLphUYuY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388618AbfEXFwV (ORCPT ); Fri, 24 May 2019 01:52:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:37754 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388260AbfEXFwU (ORCPT ); Fri, 24 May 2019 01:52:20 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 013ED20657; Fri, 24 May 2019 05:52:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558677139; bh=isQJuIhcuCBrs0hEM9Rq67SyZfcwBKSPB6Sk8DBiWws=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fP7FW/cO8V34XYmZg9rWhYsL+PlOydNwPAReC9ZvfvYHaN/b35fM+DhbXsDD67mLp bi3k1OgRmDaUQFf0FVg8SK9pE8qEzstPunr67zKr1kYB8kOlV2hBMjdlV6RYrQgZVT n3laM/k1NfzSjlro/5hQ+q4XG8fMNd+89CIJuUu4= Date: Fri, 24 May 2019 07:52:17 +0200 From: Greg Kroah-Hartman To: Saravana Kannan Cc: Rob Herring , Mark Rutland , "Rafael J. Wysocki" , Frank Rowand , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v1 0/5] Solve postboot supplier cleanup and optimize probe ordering Message-ID: <20190524055217.GC31664@kroah.com> References: <20190524010117.225219-1-saravanak@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190524010117.225219-1-saravanak@google.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 23, 2019 at 06:01:11PM -0700, Saravana Kannan wrote: > Add a generic "depends-on" property that allows specifying mandatory > functional dependencies between devices. Add device-links after the > devices are created (but before they are probed) by looking at this > "depends-on" property. > > This property is used instead of existing DT properties that specify > phandles of other devices (Eg: clocks, pinctrl, regulators, etc). This > is because not all resources referred to by existing DT properties are > mandatory functional dependencies. Some devices/drivers might be able > to operate with reduced functionality when some of the resources > aren't available. For example, a device could operate in polling mode > if no IRQ is available, a device could skip doing power management if > clock or voltage control isn't available and they are left on, etc. > > So, adding mandatory functional dependency links between devices by > looking at referred phandles in DT properties won't work as it would > prevent probing devices that could be probed. By having an explicit > depends-on property, we can handle these cases correctly. > > Having functional dependencies explicitly called out in DT and > automatically added before the devices are probed, provides the > following benefits: > > - Optimizes device probe order and avoids the useless work of > attempting probes of devices that will not probe successfully > (because their suppliers aren't present or haven't probed yet). > > For example, in a commonly available mobile SoC, registering just > one consumer device's driver at an initcall level earlier than the > supplier device's driver causes 11 failed probe attempts before the > consumer device probes successfully. This was with a kernel with all > the drivers statically compiled in. This problem gets a lot worse if > all the drivers are loaded as modules without direct symbol > dependencies. > > - Supplier devices like clock providers, regulators providers, etc > need to keep the resources they provide active and at a particular > state(s) during boot up even if their current set of consumers don't > request the resource to be active. This is because the rest of the > consumers might not have probed yet and turning off the resource > before all the consumers have probed could lead to a hang or > undesired user experience. > > Some frameworks (Eg: regulator) handle this today by turning off > "unused" resources at late_initcall_sync and hoping all the devices > have probed by then. This is not a valid assumption for systems with > loadable modules. Other frameworks (Eg: clock) just don't handle > this due to the lack of a clear signal for when they can turn off > resources. This leads to downstream hacks to handle cases like this > that can easily be solved in the upstream kernel. > > By linking devices before they are probed, we give suppliers a clear > count of the number of dependent consumers. Once all of the > consumers are active, the suppliers can turn off the unused > resources without making assumptions about the number of consumers. > > By default we just add device-links to track "driver presence" (probe > succeeded) of the supplier device. If any other functionality provided > by device-links are needed, it is left to the consumer/supplier > devices to change the link when they probe. Somewhere in this wall of text you need to say: MAKES DEVICES BOOT FASTER! right? :) So in short, this solves the issue of deferred probing with systems with loads of modules for platform devices and device tree, in that now you have a chance to probe devices in the correct order saving loads of busy loops. A good thing, I like this, very nice work, all of these are: Reviewed-by: Greg Kroah-Hartman but odds are I'll take this through my tree, so I'll add my s-o-b then. But only after the DT people agree on the new entry. thanks, greg k-h