Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752768Ab3C0LJW (ORCPT ); Wed, 27 Mar 2013 07:09:22 -0400 Received: from www.linutronix.de ([62.245.132.108]:34419 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751407Ab3C0LJU (ORCPT ); Wed, 27 Mar 2013 07:09:20 -0400 Date: Wed, 27 Mar 2013 12:09:17 +0100 (CET) From: Thomas Gleixner To: Ulf Hansson cc: Viresh Kumar , Mike Turquette , linaro-kernel@lists.linaro.org, patches@linaro.org, linux-kernel@vger.kernel.org, Laurent Pinchart , David Brown , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v4] clk: allow reentrant calls into the clk framework In-Reply-To: Message-ID: References: <1364368183-24420-1-git-send-email-mturquette@linaro.org> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2111 Lines: 59 On Wed, 27 Mar 2013, Ulf Hansson wrote: > On 27 March 2013 10:55, Viresh Kumar wrote: > > On 27 March 2013 15:10, Thomas Gleixner wrote: > >> On Wed, 27 Mar 2013, Mike Turquette wrote: > >> > >>> Reentrancy into the clock framework from the clk.h api is necessary > >>> for clocks that are prepared and unprepared via i2c_transfer (which > >>> includes many PMICs and discrete audio chips) as well as for several > >>> other use cases. > >> > >> That explanation sucks. > >> > >> Why does an i2c clock need reentrancy? Just because it's i2c or what? > > > > I am noway connected to this development but was just going through > > your mail and i think i might know the answer why is this required. > > > > Consider an example where an external chip has clock controller and has > > bits which can be programmed to enable/disable clock. And this chip is > > connected via spi/i2c to SoC. > > > > clk_prepare(peripheral on external chip) > > -> i2c_xfer(to write to external chips register) > > -> clk_enable(i2c controller) > > ->controller-xfer-routine.. and finally we enable clk here... Which does not explain the whole issue: clk_prepare() takes the mutex clk_enable() takes the spinlock That works today. The issue arises, if you need to call clk_prepare(i2c) in the xfer routine. > > > > Sorry if i am on the wrong side :) Only slightly :) > I agree with you Viresh. I guess Mike should update the commit message. > > I would also like add another reason to why this is needed. For some > clks you would like to do pinctrl operations from a clk hw. But since > a pinctrl driver likely requires a clk to be prepared|enabled, we run > into a clk reentrant issue. Fair enough. This all wants to go into the changelog, so we can understand why we have this business. Thanks, tglx -- 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/