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=-6.8 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 5C32EECDE46 for ; Thu, 25 Oct 2018 08:12:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0756420834 for ; Thu, 25 Oct 2018 08:12:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=baylibre-com.20150623.gappssmtp.com header.i=@baylibre-com.20150623.gappssmtp.com header.b="ZUYI/lOo" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0756420834 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=baylibre.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727231AbeJYQoa (ORCPT ); Thu, 25 Oct 2018 12:44:30 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:41183 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726819AbeJYQoa (ORCPT ); Thu, 25 Oct 2018 12:44:30 -0400 Received: by mail-wr1-f67.google.com with SMTP id q7-v6so8265425wrr.8 for ; Thu, 25 Oct 2018 01:12:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=baylibre-com.20150623.gappssmtp.com; s=20150623; h=message-id:subject:from:to:cc:date:in-reply-to:references :mime-version:content-transfer-encoding; bh=KTeD11N2vcL/PBm+5Cn40Nag7y2olhmRH2A174v2JwI=; b=ZUYI/lOodPJNRh4rvtYLxhpm9HoF/T9tHT8GaJeVU38UnMrD3Dpk3wBixblysQLUWK QZAqe9I1cy2CM7dX3ynWGGqfJgGwif54gFfPlSD7yh7PQwhdvLnoceWriU6o5UI7hOiP HUFEqZMpKwVxz18QwI/2RVT4T4Tf8Gu09GvCrMFKrsAtNpIMC9u0lijqasb8nexk6NJl DrH7WZxqJoJcQ4+IuB0WD+wGdGPofWpK/KNijXgZx260FHU+iptX9DpaAMgenfVKihXw k6oQ4Aj8VQDR0O2grpKU1BDLwRW3J6h2Yuo++H9xUTW/KgXteTuAO+WoweXuNTJBVWTQ umbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:mime-version:content-transfer-encoding; bh=KTeD11N2vcL/PBm+5Cn40Nag7y2olhmRH2A174v2JwI=; b=Fc0nkoPnn8qRueey/6IJQvzK46JZ0HWQbbNpWB4L7Lgd/NEmR/fVQi3CVTguEkG3V4 gRWAt6gP4A60PkDu2tkxSlf7+lw39x9vBqGQaoDANYA5JNPzKkf3nV+rpgxQaIxcQkVj MRmi84tjb7qen5nEjNxsXPwcPqF3b8R35+HveCPOuyqXXG0UWV5Iy6N0bwK/Bpcfq+fg W31vfK6OaLn12FzkeyJWiEBASEI/w95sfgf/bHdfRH8Gunrogcp6Bf6bT8/KsZMUSfxn mqQy8kJWDe61c98zIHaOmkT1dz+LLtjf9WOUGvg47fHvHrUdPzfii9wLtSvX/V0jWiYj sFnA== X-Gm-Message-State: AGRZ1gLT/TgbXunWkVO7b+ywT9AgG16hliLJpORi6Q1zjXgS82vUWgqi 88qXKDHZEI5wAggR75cCwDS2KA== X-Google-Smtp-Source: AJdET5eXT95pfSOQR0BYwdKGhUatqUlkCZpG7RLdQyouuYNMG35Ej2s1Gv3K92/eAiAwl68m8yTpKQ== X-Received: by 2002:adf:eec1:: with SMTP id a1-v6mr790559wrp.242.1540455168013; Thu, 25 Oct 2018 01:12:48 -0700 (PDT) Received: from boomer ([90.63.244.31]) by smtp.gmail.com with ESMTPSA id 4-v6sm3428259wrk.52.2018.10.25.01.12.46 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 25 Oct 2018 01:12:47 -0700 (PDT) Message-ID: <639e0498b81edf5f39b1e73efa8a3db8188d6930.camel@baylibre.com> Subject: Re: [PATCH 1/6] clk: Remove recursion in clk_core_{prepare,enable}() From: Jerome Brunet To: "dbasehore ." Cc: linux-kernel , linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, linux-doc@vger.kernel.org, sboyd@kernel.org, Michael Turquette , Heiko =?ISO-8859-1?Q?St=FCbner?= , aisheng.dong@nxp.com, mchehab+samsung@kernel.org, Jonathan Corbet , Stephen Boyd Date: Thu, 25 Oct 2018 10:12:45 +0200 In-Reply-To: References: <20181024013132.115907-1-dbasehore@chromium.org> <20181024013132.115907-2-dbasehore@chromium.org> <264adf2a81bcd602f2a58e4a46c3273cd7c77ca2.camel@baylibre.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-1.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2018-10-24 at 13:36 -0700, dbasehore . wrote: > On Wed, Oct 24, 2018 at 2:51 AM Jerome Brunet wrote: > > > > On Tue, 2018-10-23 at 18:31 -0700, Derek Basehore wrote: > > > From: Stephen Boyd > > > > > > Enabling and preparing clocks can be written quite naturally with > > > recursion. We start at some point in the tree and recurse up the > > > tree to find the oldest parent clk that needs to be enabled or > > > prepared. Then we enable/prepare and return to the caller, going > > > back to the clk we started at and enabling/preparing along the > > > way. > > > > > > The problem is recursion isn't great for kernel code where we > > > have a limited stack size. Furthermore, we may be calling this > > > code inside clk_set_rate() which also has recursion in it, so > > > we're really not looking good if we encounter a tall clk tree. > > > > > > Let's create a stack instead by looping over the parent chain and > > > collecting clks of interest. Then the enable/prepare becomes as > > > simple as iterating over that list and calling enable. > > > > Hi Derek, > > > > What about unprepare() and disable() ? > > > > This patch removes the recursion from the enable path but keeps it for the > > disable path ... this is very odd. Assuming doing so works, It certainly makes > > CCF a lot harder to understand. > > It wasn't there in the original patch. I asked Stephen, and he thinks > it may have been left that way because unprepare/disable are tail > recursion cases, which the compiler can optimize away. I'm sure the compiler is very clever ;) My point is more about maintainability and how easy it is to understand for human beings. > > > > > What about clock protection which essentially works on the same model as prepare > > and enable ? > > > > Overall, this change does not look like something that should be merged as it > > is. If you were just seeking comments, you should add the "RFC" tag to your > > series. > > > > Jerome. > > > > > > > > Cc: Jerome Brunet > > > > If you don't mind, I would prefer to get the whole series next time. It helps to > > get the context. > > > > > Signed-off-by: Stephen Boyd > > > Signed-off-by: Derek Basehore > > > --- > > > drivers/clk/clk.c | 113 ++++++++++++++++++++++++++-------------------- > > > 1 file changed, 64 insertions(+), 49 deletions(-) > > > > > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > > > index af011974d4ec..95d818f5edb2 100644 > > > --- a/drivers/clk/clk.c > > > +++ b/drivers/clk/clk.c > > > @@ -71,6 +71,8 @@ struct clk_core { > > > struct hlist_head children; > > > struct hlist_node child_node; > > > struct hlist_head clks; > > > + struct list_head prepare_list; > > > + struct list_head enable_list; > > > unsigned int notifier_count; > > > #ifdef CONFIG_DEBUG_FS > > > struct dentry *dentry; > > > @@ -740,49 +742,48 @@ EXPORT_SYMBOL_GPL(clk_unprepare); > > > static int clk_core_prepare(struct clk_core *core) > > > { > > > int ret = 0; > > > + struct clk_core *tmp, *parent; > > > + LIST_HEAD(head); > > > > > > lockdep_assert_held(&prepare_lock); > > > > > > - if (!core) > > > - return 0; > > > + while (core) { > > > + list_add(&core->prepare_list, &head); > > > + /* Stop once we see a clk that is already prepared */ > > > + if (core->prepare_count) > > > + break; > > > + core = core->parent; > > > + } > > > > > > - if (core->prepare_count == 0) { > > > - ret = clk_pm_runtime_get(core); > > > - if (ret) > > > - return ret; > > > + list_for_each_entry_safe(core, tmp, &head, prepare_list) { > > > + list_del_init(&core->prepare_list); > > > > Is there any point in removing it from the list ? > > Maybe I missed it but it does not seems useful. > > > > Without this, we could use list_for_each_entry() > > > > > > > > - ret = clk_core_prepare(core->parent); > > > - if (ret) > > > - goto runtime_put; > > > + if (core->prepare_count == 0) { > > > > Should we really check the count here ? You are not checking the count when the > > put() counterpart is called below. > > > > Since PM runtime has ref counting as well, either way would work I guess ... but > > we shall be consistent > > > > > + ret = clk_pm_runtime_get(core); > > > + if (ret) > > > + goto err; > > > > > > - trace_clk_prepare(core); > > > + trace_clk_prepare(core); > > > > > > - if (core->ops->prepare) > > > - ret = core->ops->prepare(core->hw); > > > + if (core->ops->prepare) > > > + ret = core->ops->prepare(core->hw); > > > > > > - trace_clk_prepare_complete(core); > > > + trace_clk_prepare_complete(core); > > > > > > - if (ret) > > > - goto unprepare; > > > + if (ret) { > > > + clk_pm_runtime_put(core); > > > + goto err; > > > + } > > > + } > > > + core->prepare_count++; > > > } > > > > > > - core->prepare_count++; > > > - > > > - /* > > > - * CLK_SET_RATE_GATE is a special case of clock protection > > > - * Instead of a consumer claiming exclusive rate control, it is > > > - * actually the provider which prevents any consumer from making any > > > - * operation which could result in a rate change or rate glitch while > > > - * the clock is prepared. > > > - */ > > > - if (core->flags & CLK_SET_RATE_GATE) > > > - clk_core_rate_protect(core); > > > > This gets removed without anything replacing it. > > > > is CLK_SET_RATE_GATE and clock protection support dropped after this change ? > > > > > - > > > return 0; > > > -unprepare: > > > - clk_core_unprepare(core->parent); > > > -runtime_put: > > > - clk_pm_runtime_put(core); > > > +err: > > > + parent = core->parent; > > > + list_for_each_entry_safe_continue(core, tmp, &head, prepare_list) > > > + list_del_init(&core->prepare_list); > > > + clk_core_unprepare(parent); > > > > If you get here because of failure clk_pm_runtime_get(), you will unprepare a > > clock which may have not been prepared first > > > > Overall the rework of error exit path does not seem right (or necessary) > > > > > return ret; > > > } > > > > > > @@ -878,37 +879,49 @@ EXPORT_SYMBOL_GPL(clk_disable); > > > static int clk_core_enable(struct clk_core *core) > > > { > > > int ret = 0; > > > + struct clk_core *tmp, *parent; > > > + LIST_HEAD(head); > > > > > > lockdep_assert_held(&enable_lock); > > > > > > - if (!core) > > > - return 0; > > > - > > > - if (WARN(core->prepare_count == 0, > > > - "Enabling unprepared %s\n", core->name)) > > > - return -ESHUTDOWN; > > > + while (core) { > > > + list_add(&core->enable_list, &head); > > > + /* Stop once we see a clk that is already enabled */ > > > + if (core->enable_count) > > > + break; > > > + core = core->parent; > > > + } > > > > > > - if (core->enable_count == 0) { > > > - ret = clk_core_enable(core->parent); > > > + list_for_each_entry_safe(core, tmp, &head, enable_list) { > > > + list_del_init(&core->enable_list); > > > > > > - if (ret) > > > - return ret; > > > + if (WARN_ON(core->prepare_count == 0)) { > > > + ret = -ESHUTDOWN; > > > + goto err; > > > + } > > > > > > - trace_clk_enable_rcuidle(core); > > > + if (core->enable_count == 0) { > > > + trace_clk_enable_rcuidle(core); > > > > > > - if (core->ops->enable) > > > - ret = core->ops->enable(core->hw); > > > + if (core->ops->enable) > > > + ret = core->ops->enable(core->hw); > > > > > > - trace_clk_enable_complete_rcuidle(core); > > > + trace_clk_enable_complete_rcuidle(core); > > > > > > - if (ret) { > > > - clk_core_disable(core->parent); > > > - return ret; > > > + if (ret) > > > + goto err; > > > } > > > + > > > + core->enable_count++; > > > } > > > > > > - core->enable_count++; > > > return 0; > > > +err: > > > + parent = core->parent; > > > + list_for_each_entry_safe_continue(core, tmp, &head, enable_list) > > > + list_del_init(&core->enable_list); > > > + clk_core_disable(parent); > > > + return ret; > > > } > > > > > > static int clk_core_enable_lock(struct clk_core *core) > > > @@ -3281,6 +3294,8 @@ struct clk *clk_register(struct device *dev, struct clk_hw *hw) > > > core->num_parents = hw->init->num_parents; > > > core->min_rate = 0; > > > core->max_rate = ULONG_MAX; > > > + INIT_LIST_HEAD(&core->prepare_list); > > > + INIT_LIST_HEAD(&core->enable_list); > > > hw->core = core; > > > > > > /* allocate local copy in case parent_names is __initdata */ > > > >