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Received: from shell.armlinux.org.uk ([2002:4e20:1eda:1:5054:ff:fe00:4ec]:47872) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ifPjP-0007Hs-GT; Thu, 12 Dec 2019 14:46:19 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1ifPjM-0006tX-JX; Thu, 12 Dec 2019 14:46:16 +0000 Date: Thu, 12 Dec 2019 14:46:16 +0000 From: Russell King - ARM Linux admin To: Marc Gonzalez Subject: Re: [PATCH v1] clk: Convert managed get functions to devm_add_action API Message-ID: <20191212144616.GJ25745@shell.armlinux.org.uk> 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> <58c27422-e06c-f42e-16ea-baeca3bb9b01@free.fr> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <58c27422-e06c-f42e-16ea-baeca3bb9b01@free.fr> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191212_064632_781736_5F1FF353 X-CRM114-Status: GOOD ( 18.65 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kuninori Morimoto , Stephen Boyd , Michael Turquette , Dmitry Torokhov , linux-clk , LKML , Bjorn Andersson , Linux ARM , Robin Murphy , Sudip Mukherjee , Guenter Roeck Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Dec 12, 2019 at 03:41:20PM +0100, Marc Gonzalez wrote: > 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); Okay. However, please don't call this __clk_put(). git grep __clk_put will tell you why. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel