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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 3374EC4360C for ; Fri, 4 Oct 2019 15:34:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0B8B8222C2 for ; Fri, 4 Oct 2019 15:34:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570203259; bh=0xz0v9CS90Mf5SnJsRIjoR0Jp0BEQdT9kMWX10qH82k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=iDFfEjYtBEOZEIiQRYFvtPXe9hhAX3pX6eJFcGAChQjjyi4nJyUUBcRCTzuIUXmfo yDQOnJc4ZLZTCpeEQJx5B1kihfuQWRj9CX8dwDyT/B/5fm1kGDScMmT7sNspKqJuBU ganPZz/0mPnr57rHW01uW17wK1Ou03OTljnqpDrY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389871AbfJDPeS (ORCPT ); Fri, 4 Oct 2019 11:34:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:60292 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389318AbfJDPeS (ORCPT ); Fri, 4 Oct 2019 11:34:18 -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 396A720873; Fri, 4 Oct 2019 15:34:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570203256; bh=0xz0v9CS90Mf5SnJsRIjoR0Jp0BEQdT9kMWX10qH82k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=y3oy5JYQ+cihYLJ2Bu+FaM7G8smtISpSqtlSC7M060J+ceVEI4eeNN19m4Jjwvb/y 4JQ9N4DnypAMta9u2EefrUo+KPJ3J9ipiZBJ8YwRvPJ+JSMkD4U1bvV/DnuLEEtepF vX0JbYsgPj98yzWCzr8zbRKS79Kv+63IugMHKlBU= Date: Fri, 4 Oct 2019 17:34:14 +0200 From: Greg Kroah-Hartman To: Saravana Kannan Cc: Rob Herring , Mark Rutland , "Rafael J. Wysocki" , Frank Rowand , Jonathan Corbet , Len Brown , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-acpi@vger.kernel.org, clang-built-linux@googlegroups.com, David Collins , kernel-team@android.com Subject: Re: [PATCH v11 0/6] Solve postboot supplier cleanup and optimize probe ordering Message-ID: <20191004153414.GA823823@kroah.com> References: <20190904211126.47518-1-saravanak@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904211126.47518-1-saravanak@google.com> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 04, 2019 at 02:11:19PM -0700, Saravana Kannan wrote: > Add device-links to track functional dependencies between devices > after they are created (but before they are probed) by looking at > their common DT bindings like clocks, interconnects, etc. > > Having functional dependencies 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, interconnect 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. Hearing no real complaints again, I've now queued these up in my tree. thanks, greg k-h