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=-5.0 required=3.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 C061BC2D0C9 for ; Thu, 12 Dec 2019 14:41:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9EAE922527 for ; Thu, 12 Dec 2019 14:41:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729709AbfLLOlW (ORCPT ); Thu, 12 Dec 2019 09:41:22 -0500 Received: from ns.iliad.fr ([212.27.33.1]:59576 "EHLO ns.iliad.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729273AbfLLOlW (ORCPT ); Thu, 12 Dec 2019 09:41:22 -0500 Received: from ns.iliad.fr (localhost [127.0.0.1]) by ns.iliad.fr (Postfix) with ESMTP id BBA22200E9; Thu, 12 Dec 2019 15:41:20 +0100 (CET) Received: from [192.168.108.51] (freebox.vlq16.iliad.fr [213.36.7.13]) by ns.iliad.fr (Postfix) with ESMTP id A1FA5200E6; Thu, 12 Dec 2019 15:41:20 +0100 (CET) Subject: Re: [PATCH v1] clk: Convert managed get functions to devm_add_action API To: Russell King - ARM Linux admin Cc: Dmitry Torokhov , Robin Murphy , Bjorn Andersson , Kuninori Morimoto , Stephen Boyd , Michael Turquette , LKML , Sudip Mukherjee , Guenter Roeck , linux-clk , Linux ARM References: <3d8a58bf-0814-1ec1-038a-10a20b9646ad@free.fr> <20191128185630.GK82109@yoga> <20191202014237.GR248138@dtor-ws> <20191211222829.GV50317@dtor-ws> <70528f77-ca10-01cd-153b-23486ce87d45@free.fr> <20191212141747.GI25745@shell.armlinux.org.uk> From: Marc Gonzalez Message-ID: <58c27422-e06c-f42e-16ea-baeca3bb9b01@free.fr> Date: Thu, 12 Dec 2019 15:41:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: <20191212141747.GI25745@shell.armlinux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Virus-Scanned: ClamAV using ClamSMTP ; ns.iliad.fr ; Thu Dec 12 15:41:20 2019 +0100 (CET) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/12/2019 15:17, Russell King - ARM Linux admin wrote: > On Thu, Dec 12, 2019 at 02:53:40PM +0100, Marc Gonzalez wrote: > >> On 11/12/2019 23:28, Dmitry Torokhov wrote: >> >>> On Wed, Dec 11, 2019 at 05:17:28PM +0100, Marc Gonzalez wrote: >>> >>>> What is the rationale for the devm_add_action API? >>> >>> For one-off and maybe complex unwind actions in drivers that wish to use >>> devm API (as mixing devm and manual release is verboten). Also is often >>> used when some core subsystem does not provide enough devm APIs. >> >> Thanks for the insight, Dmitry. Thanks to Robin too. >> >> This is what I understand so far: >> >> devm_add_action() is nice because it hides/factorizes the complexity >> of the devres API, but it incurs a small storage overhead of one >> pointer per call, which makes it unfit for frequently used actions, >> such as clk_get. >> >> Is that correct? >> >> My question is: why not design the API without the small overhead? >> >> Proof of concept below: >> >> >> diff --git a/drivers/base/devres.c b/drivers/base/devres.c >> index 0bbb328bd17f..76392dd6273b 100644 >> --- a/drivers/base/devres.c >> +++ b/drivers/base/devres.c >> @@ -685,6 +685,20 @@ int devres_release_group(struct device *dev, void *id) >> } >> EXPORT_SYMBOL_GPL(devres_release_group); >> >> +void *devm_add(struct device *dev, dr_release_t func, void *arg, size_t size) >> +{ >> + void *data = devres_alloc(func, size, GFP_KERNEL); >> + >> + if (data) { >> + memcpy(data, arg, size); >> + devres_add(dev, data); >> + } else >> + func(dev, arg); >> + >> + return data; >> +} >> +EXPORT_SYMBOL_GPL(devm_add); >> + >> /* >> * Custom devres actions allow inserting a simple function call >> * into the teadown sequence. >> diff --git a/drivers/clk/clk-devres.c b/drivers/clk/clk-devres.c >> index be160764911b..8db671823126 100644 >> --- a/drivers/clk/clk-devres.c >> +++ b/drivers/clk/clk-devres.c >> @@ -4,6 +4,11 @@ >> #include >> #include >> >> +static void __clk_put(struct device *dev, void *data) >> +{ >> + clk_put(*(struct clk **)data); >> +} >> + >> static void devm_clk_release(struct device *dev, void *res) >> { >> clk_put(*(struct clk **)res); >> @@ -11,19 +16,11 @@ static void devm_clk_release(struct device *dev, void *res) >> >> struct clk *devm_clk_get(struct device *dev, const char *id) >> { >> - struct clk **ptr, *clk; >> - >> - ptr = devres_alloc(devm_clk_release, sizeof(*ptr), GFP_KERNEL); >> - if (!ptr) >> - return ERR_PTR(-ENOMEM); >> + struct clk *clk = clk_get(dev, id); >> >> - clk = clk_get(dev, id); >> - if (!IS_ERR(clk)) { >> - *ptr = clk; >> - devres_add(dev, ptr); >> - } else { >> - devres_free(ptr); >> - } >> + if (!IS_ERR(clk)) >> + if (!devm_add(dev, __clk_put, &clk, sizeof(clk))) >> + clk = ERR_PTR(-ENOMEM); > > You leak clk here. I don't think so ;-) If devm_add() returns NULL, then we have called __clk_put(dev, &clk); Regards.