Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753671AbaAVGD2 (ORCPT ); Wed, 22 Jan 2014 01:03:28 -0500 Received: from mail-la0-f49.google.com ([209.85.215.49]:46025 "EHLO mail-la0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751856AbaAVGC6 (ORCPT ); Wed, 22 Jan 2014 01:02:58 -0500 MIME-Version: 1.0 Date: Wed, 22 Jan 2014 14:02:57 +0800 Message-ID: Subject: mutual exculsion between clk_prepare_enable /clk_disable_unprepare and clk_set_parent From: Xiaoguang Chen To: mturquette@linaro.org Cc: Xiaoguang Chen , Zhoujie Wu , cxie4@marvell.com, linux-arm-kernel@lists.infradead.org, "linux-kernel@vger.kernel.org" , lucao@marvell.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 Hi, Mike We met a issue between clk_prepare_enable /clk_disable_unprepare and clk_set_parent. As we know, clk preprare/unprare will grab preprare lock, and clk enable/disable will grab enable lock. clk_set_parent will grab prepare lock but there is no lock protection in clk_prepare_enable /clk_disable_unprepare, for example, in clk_disable_unprepare, it is expended as clk_disable + clk_unprepare, and if below condition occurs, there will be problem thread1 thread 2 call clk_disable_unprepare 1) clk_disable get enable lock ............... release enable lock call clk_set_parent get prepare lock set clock's parent to another parent release prepare lock 2) clk_unprepare get prepare lock unprepare parent clock <<-------------- release prepare lock In above sequence, After thread 1 call clock disable, thread 2 change clk's parent to another clock, then in thread1 step2, it will unprepare clk's new parent, but not old parent, this will cause old parent is not unprepared, but new parent is unprepared even when it is not prepared yet. So How can we use this API: clk_prepare_enable and clk_disable_unprepare ? Should we add lock to protect this API, if we get a prepare lock inside this API, like clk_disable_unprepare () { get_prepare_lock(); clk_disable(); clk_unprepare(); clk_prepare_unlock(); } is above sequence ok? if so, I can provide a patch for this. Thanks Xiaoguang -- 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/