Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751193AbbB1HxG (ORCPT ); Sat, 28 Feb 2015 02:53:06 -0500 Received: from mx08-00178001.pphosted.com ([91.207.212.93]:36281 "EHLO mx08-00178001.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750766AbbB1HxC (ORCPT ); Sat, 28 Feb 2015 02:53:02 -0500 Message-ID: <54F173B7.9030305@st.com> Date: Sat, 28 Feb 2015 08:52:23 +0100 From: Maxime Coquelin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Lee Jones , , CC: , , , Subject: Re: [STLinux Kernel] [PATCH 3/4] clk: Provide always-on clock support References: <1425071674-16995-1-git-send-email-lee.jones@linaro.org> <1425071674-16995-4-git-send-email-lee.jones@linaro.org> In-Reply-To: <1425071674-16995-4-git-send-email-lee.jones@linaro.org> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.251.16.38] X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.13.68,1.0.33,0.0.0000 definitions=2015-02-28_01:2015-02-27,2015-02-28,1970-01-01 signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1354 Lines: 32 Hi Lee, On 02/27/2015 10:14 PM, Lee Jones wrote: > Lots of platforms contain clocks which if turned off would prove fatal. > The only way to recover from these catastrophic failures is to restart > the board(s). Now, when a clock is registered with the framework it is > compared against a list of provided always-on clock names which must be > kept ungated. If it matches, we enable the existing CLK_IGNORE_UNUSED > flag, which will prevent the common clk framework from attempting to > gate it during the clk_disable_unused() procedure. Please correct me if I'm wrong, but your patch does not fix the issue you had initially. Let's take an example: A clock is critical for the system, and should never be gated, so you add the CLK_IGNORE_UNUSED flag so that it is not disabled by clk_disable_unused() procedure. The same clock is also used by other IPs, for example spi 0 instance. When starting a spi transfer, clk_enable() is called on this clock, so its usecount becomes 1. Once transfer done, clk_disable() is called, usecount becomes 0 and the clock gets disabled: system freeze. BR, Maxime -- 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/