From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-13.3 required=5.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE, USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 524417D2F0 for ; Mon, 8 Jul 2019 22:56:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728420AbfGHW4f (ORCPT ); Mon, 8 Jul 2019 18:56:35 -0400 Received: from mail-qt1-f202.google.com ([209.85.160.202]:34488 "EHLO mail-qt1-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728252AbfGHW4f (ORCPT ); Mon, 8 Jul 2019 18:56:35 -0400 Received: by mail-qt1-f202.google.com with SMTP id p34so17786560qtp.1 for ; Mon, 08 Jul 2019 15:56:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=XvWJ9Wo8dlDTDdNMofIJHczNPs27/UWoPes3SLfO5XU=; b=WclkCq5NSEjgs6nde0M1rMmrM65BjUj2nOtAptw+49lxPVnTilWsk30clsG33/DaNQ cVKQtE3HmsVxEW0zRVDGc4Qw+NrMaNVJ5/Y5OtE1Ys/+tzz8WwOftxceMNH8H0yBlNne MualKveXJ29JQkSo4suCUaq9gmcZ24iNJ77cAMyC+34DOjcsMtpP7NU2lKkx/ztLHmFz uU8OoOtQK1byDXLzJS9SFuFSov1sl7//RnsDTP0EW+I0kKI/5aUWBCawmJvjw/tQGpgm i0VNNv9dYeu3r2qgsBUht8Bqwr2tWRss678RUy/mD47OoMizRcTzwokIWT4ycCv//yup IzaA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=XvWJ9Wo8dlDTDdNMofIJHczNPs27/UWoPes3SLfO5XU=; b=I1SRCFRZWKih1rVvygf4hWgyjAmhi/9em+Xpsj0Il0Wo04YANPmjCqncf9kbEoyFdc ZEctaD7WhKRhes1cB7kmgDA6HQCVUttGvotE+izKChFqtqWMc0JaYu5lbJinWpxb82Ct SE44Pef11fvj64wVZRpoj/i1rhJU9EBK6JX65qYF4xaR6O6Vq7bkleWZ51D62Cbo5jFV HwS8aM81nq5Jo7PbcUnLn/imYxbQPZlc3lBDp2bp5QBen6BjZiFrx48UzTbdujgtQRxu L3hv2GF5XZfCLFC2DB4Q/4xqnuarYoPwNgVLjie8klTUqouTUB7V+6VII33hu4dFrBLq AIkA== X-Gm-Message-State: APjAAAUZCejHX5PngHFL1opbaH6/xL8QQ5xX6cEt4fQwXJjgfzEFhR8n Vvdqlryk6yAn6JLZVdfRiS77Bqvytr87KkM= X-Google-Smtp-Source: APXvYqz1MM+h/XGVDaDwHBQY/KGtEfMQBAFIOn1giKJq1+6cKbx1GmCSmWPye2hV9fTTgYSYshDB8uV50jvTHe4= X-Received: by 2002:a0c:df12:: with SMTP id g18mr15652833qvl.34.1562626594509; Mon, 08 Jul 2019 15:56:34 -0700 (PDT) Date: Mon, 8 Jul 2019 15:56:18 -0700 In-Reply-To: <20190708225624.119973-1-saravanak@google.com> Message-Id: <20190708225624.119973-3-saravanak@google.com> Mime-Version: 1.0 References: <20190708225624.119973-1-saravanak@google.com> X-Mailer: git-send-email 2.22.0.410.gd8fdbe21b5-goog Subject: [PATCH v4 2/8] of/platform: Add functional dependency link from DT bindings From: Saravana Kannan To: Rob Herring , Mark Rutland , Greg Kroah-Hartman , "Rafael J. Wysocki" , Frank Rowand , Jonathan Corbet Cc: Saravana Kannan , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, David Collins , kernel-team@android.com, linux-doc@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Add device-links after the devices are created (but before they are probed) by looking at common DT bindings like clocks and interconnects. Automatically adding device-links for functional dependencies at the framework level 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. Signed-off-by: Saravana Kannan --- .../admin-guide/kernel-parameters.txt | 5 ++ drivers/of/platform.c | 57 +++++++++++++++++++ 2 files changed, 62 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 138f6664b2e2..109b4310844f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3141,6 +3141,11 @@ This can be set from sysctl after boot. See Documentation/sysctl/vm.txt for details. + of_devlink [KNL] Make device links from common DT bindings. Useful + for optimizing probe order and making sure resources + aren't turned off before the consumer devices have + probed. + ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. See Documentation/debugging-via-ohci1394.txt for more info. diff --git a/drivers/of/platform.c b/drivers/of/platform.c index 04ad312fd85b..0930f9f89571 100644 --- a/drivers/of/platform.c +++ b/drivers/of/platform.c @@ -509,6 +509,62 @@ int of_platform_default_populate(struct device_node *root, } EXPORT_SYMBOL_GPL(of_platform_default_populate); +static int of_link_binding(struct device *dev, + const char *binding, const char *cell) +{ + struct of_phandle_args sup_args; + struct platform_device *sup_dev; + unsigned int i = 0, links = 0; + u32 dl_flags = DL_FLAG_AUTOPROBE_CONSUMER; + + while (!of_parse_phandle_with_args(dev->of_node, binding, cell, i, + &sup_args)) { + i++; + sup_dev = of_find_device_by_node(sup_args.np); + of_node_put(sup_args.np); + if (!sup_dev) + continue; + if (device_link_add(dev, &sup_dev->dev, dl_flags)) + links++; + put_device(&sup_dev->dev); + } + if (links < i) + return -ENODEV; + return 0; +} + +static bool of_devlink; +core_param(of_devlink, of_devlink, bool, 0); + +/* + * List of bindings and their cell names (use NULL if no cell names) from which + * device links need to be created. + */ +static const char * const link_bindings[] = { + "clocks", "#clock-cells", + "interconnects", "#interconnect-cells", +}; + +static int of_link_to_suppliers(struct device *dev) +{ + unsigned int i = 0; + bool done = true; + + if (!of_devlink) + return 0; + if (unlikely(!dev->of_node)) + return 0; + + for (i = 0; i < ARRAY_SIZE(link_bindings) / 2; i++) + if (of_link_binding(dev, link_bindings[i * 2], + link_bindings[i * 2 + 1])) + done = false; + + if (!done) + return -ENODEV; + return 0; +} + #ifndef CONFIG_PPC static const struct of_device_id reserved_mem_matches[] = { { .compatible = "qcom,rmtfs-mem" }, @@ -524,6 +580,7 @@ static int __init of_platform_default_populate_init(void) if (!of_have_populated_dt()) return -ENODEV; + platform_bus_type.add_links = of_link_to_suppliers; /* * Handle certain compatibles explicitly, since we don't want to create * platform_devices for every node in /reserved-memory with a -- 2.22.0.410.gd8fdbe21b5-goog