Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756353Ab3C1PXq (ORCPT ); Thu, 28 Mar 2013 11:23:46 -0400 Received: from mail-wi0-f173.google.com ([209.85.212.173]:45090 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755605Ab3C1PXo (ORCPT ); Thu, 28 Mar 2013 11:23:44 -0400 MIME-Version: 1.0 In-Reply-To: References: <1364368183-24420-1-git-send-email-mturquette@linaro.org> <1364445958-2999-1-git-send-email-mturquette@linaro.org> <1364445958-2999-3-git-send-email-mturquette@linaro.org> From: Mike Turquette Date: Thu, 28 Mar 2013 08:23:22 -0700 Message-ID: Subject: Re: [PATCH 2/2] clk: allow reentrant calls into the clk framework To: Thomas Gleixner Cc: "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Patch Tracking , linaro-kernel@lists.linaro.org, Rajagopal Venkat , David Brown , Ulf Hansson , laurent.pinchart@ideasonboard.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1950 Lines: 43 On Thu, Mar 28, 2013 at 2:33 AM, Thomas Gleixner wrote: > On Wed, 27 Mar 2013, Mike Turquette wrote: > >> Reentrancy into the clock framework is necessary for clock operations >> that result in nested calls to the clk api. A common example is a clock >> that is prepared via an i2c transaction, such as a clock inside of a >> discrete audio chip or a power management IC. The i2c subsystem itself >> will use the clk api resulting in a deadlock: >> >> clk_prepare(audio_clk) >> i2c_transfer(..) >> clk_prepare(i2c_controller_clk) >> >> The ability to reenter the clock framework prevents this deadlock. >> >> Other use cases exist such as allowing .set_rate callbacks to call >> clk_set_parent to achieve the best rate, or to save power in certain >> configurations. Yet another example is performing pinctrl operations >> from a clk_ops callback. Calls into the pinctrl subsystem may call >> clk_{un}prepare on an unrelated clock. Allowing for nested calls to >> reenter the clock framework enables both of these use cases. >> >> Reentrancy is implemented by two global pointers that track the owner >> currently holding a global lock. One pointer tracks the owner during >> sleepable, mutex-protected operations and the other one tracks the owner >> during non-interruptible, spinlock-protected operations. >> >> When the clk framework is entered we try to hold the global lock. If it >> is held we compare the current task id against the current owner; a > > s/task id/task/ We store a the task pointer in the owner variable. > > Reviewed-by: Thomas Gleixner Will fix the typo and add your reviewed-by. Thanks for the review, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/