From mboxrd@z Thu Jan 1 00:00:00 1970 From: emilio@elopez.com.ar (=?ISO-8859-1?Q?Emilio_L=F3pez?=) Date: Mon, 24 Feb 2014 21:30:05 -0300 Subject: [PATCH 1/5] clk: sun6i: Protect CPU clock In-Reply-To: <20140225000154.GR21483@n2100.arm.linux.org.uk> References: <1393258967-4843-1-git-send-email-maxime.ripard@free-electrons.com> <1393258967-4843-2-git-send-email-maxime.ripard@free-electrons.com> <20140224163034.GN21483@n2100.arm.linux.org.uk> <530BD804.5090806@elopez.com.ar> <20140225000154.GR21483@n2100.arm.linux.org.uk> Message-ID: <530BE40D.8080506@elopez.com.ar> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Russell, El 24/02/14 21:01, Russell King - ARM Linux escribi?: > Hi Emilio. > > On Mon, Feb 24, 2014 at 08:38:44PM -0300, Emilio L?pez wrote: >> Why is this so? Can't a clock be left enabled while nobody has a >> reference to it? I have looked around in Documentation/ (rather quickly >> I must say) and have not found any explicit mention that it is required >> to keep a reference to the clock while it's enabled. I'd appreciate it >> if you could explain this a bit more verbosely or point me to the >> relevant documents. > > First up, if you have a requirement that a clock be enabled, then is it > not unreasonable to ensure that the clock is referenced? I was under the impression that the reference count was orthogonal to the clock status, but after getting that clarified, I can see your point. > Secondly, what if we have code which scans the clocks in the system, > shutting down those leaf clocks which appear to be unreferenced? Indeed, that would break things. > Thirdly, the API (as I designed it) says so: > > /** > * clk_put - "free" the clock source > * @clk: clock source > * > * Note: drivers must ensure that all clk_enable calls made on this > * clock source are balanced by clk_disable calls prior to calling > * this function. > * > * clk_put should not be called from within interrupt context. > */ > void clk_put(struct clk *clk); > > which has been there since the API was first created - it's part of the > contract between drivers using the API and implementers creating something > which conforms to the API - which today means CCF. That's enough of a reason on its own :) I should have checked clk.h > The intention here is that while there are any users holding a clk_get() > reference on a clock, the clock is assumed to be required for some > device, and the struct clk may not be kfree'd, nor may its state be > changed in an unpredictable way to those drivers holding a reference > to it. I understand now, thanks for the insight. I'll talk with Maxime and get this sorted out. As a side note, should drivers/base/power/clock_ops.c be fixed too? I have added Rafael to Cc. Cheers, Emilio From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Emilio_L=F3pez?= Subject: Re: [PATCH 1/5] clk: sun6i: Protect CPU clock Date: Mon, 24 Feb 2014 21:30:05 -0300 Message-ID: <530BE40D.8080506@elopez.com.ar> References: <1393258967-4843-1-git-send-email-maxime.ripard@free-electrons.com> <1393258967-4843-2-git-send-email-maxime.ripard@free-electrons.com> <20140224163034.GN21483@n2100.arm.linux.org.uk> <530BD804.5090806@elopez.com.ar> <20140225000154.GR21483@n2100.arm.linux.org.uk> Reply-To: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20140225000154.GR21483-l+eeeJia6m9vn6HldHNs0ANdhmdF6hFW@public.gmane.org> List-Post: , List-Help: , List-Archive: Sender: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org List-Subscribe: , List-Unsubscribe: , To: Russell King - ARM Linux Cc: Maxime Ripard , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Mike Turquette , Vinod Koul , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Dan Williams , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, rjw-KKrjLPT3xs0@public.gmane.org List-Id: devicetree@vger.kernel.org Hi Russell, El 24/02/14 21:01, Russell King - ARM Linux escribi=F3: > Hi Emilio. > > On Mon, Feb 24, 2014 at 08:38:44PM -0300, Emilio L=F3pez wrote: >> Why is this so? Can't a clock be left enabled while nobody has a >> reference to it? I have looked around in Documentation/ (rather quickly >> I must say) and have not found any explicit mention that it is required >> to keep a reference to the clock while it's enabled. I'd appreciate it >> if you could explain this a bit more verbosely or point me to the >> relevant documents. > > First up, if you have a requirement that a clock be enabled, then is it > not unreasonable to ensure that the clock is referenced? I was under the impression that the reference count was orthogonal to=20 the clock status, but after getting that clarified, I can see your point. > Secondly, what if we have code which scans the clocks in the system, > shutting down those leaf clocks which appear to be unreferenced? Indeed, that would break things. > Thirdly, the API (as I designed it) says so: > > /** > * clk_put - "free" the clock source > * @clk: clock source > * > * Note: drivers must ensure that all clk_enable calls made on this > * clock source are balanced by clk_disable calls prior to calling > * this function. > * > * clk_put should not be called from within interrupt context. > */ > void clk_put(struct clk *clk); > > which has been there since the API was first created - it's part of the > contract between drivers using the API and implementers creating somethin= g > which conforms to the API - which today means CCF. That's enough of a reason on its own :) I should have checked clk.h > The intention here is that while there are any users holding a clk_get() > reference on a clock, the clock is assumed to be required for some > device, and the struct clk may not be kfree'd, nor may its state be > changed in an unpredictable way to those drivers holding a reference > to it. I understand now, thanks for the insight. I'll talk with Maxime and get=20 this sorted out. As a side note, should drivers/base/power/clock_ops.c be fixed too? I=20 have added Rafael to Cc. Cheers, Emilio --=20 You received this message because you are subscribed to the Google Groups "= linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to linux-sunxi+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit https://groups.google.com/groups/opt_out. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753366AbaBYAaZ (ORCPT ); Mon, 24 Feb 2014 19:30:25 -0500 Received: from yotta.elopez.com.ar ([31.220.24.173]:45831 "EHLO yotta.elopez.com.ar" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752463AbaBYAaV (ORCPT ); Mon, 24 Feb 2014 19:30:21 -0500 Message-ID: <530BE40D.8080506@elopez.com.ar> Date: Mon, 24 Feb 2014 21:30:05 -0300 From: =?ISO-8859-1?Q?Emilio_L=F3pez?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Russell King - ARM Linux CC: Maxime Ripard , devicetree@vger.kernel.org, Mike Turquette , Vinod Koul , linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com, dmaengine@vger.kernel.org, Dan Williams , linux-arm-kernel@lists.infradead.org, rjw@sisk.pl Subject: Re: [PATCH 1/5] clk: sun6i: Protect CPU clock References: <1393258967-4843-1-git-send-email-maxime.ripard@free-electrons.com> <1393258967-4843-2-git-send-email-maxime.ripard@free-electrons.com> <20140224163034.GN21483@n2100.arm.linux.org.uk> <530BD804.5090806@elopez.com.ar> <20140225000154.GR21483@n2100.arm.linux.org.uk> In-Reply-To: <20140225000154.GR21483@n2100.arm.linux.org.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Russell, El 24/02/14 21:01, Russell King - ARM Linux escribió: > Hi Emilio. > > On Mon, Feb 24, 2014 at 08:38:44PM -0300, Emilio López wrote: >> Why is this so? Can't a clock be left enabled while nobody has a >> reference to it? I have looked around in Documentation/ (rather quickly >> I must say) and have not found any explicit mention that it is required >> to keep a reference to the clock while it's enabled. I'd appreciate it >> if you could explain this a bit more verbosely or point me to the >> relevant documents. > > First up, if you have a requirement that a clock be enabled, then is it > not unreasonable to ensure that the clock is referenced? I was under the impression that the reference count was orthogonal to the clock status, but after getting that clarified, I can see your point. > Secondly, what if we have code which scans the clocks in the system, > shutting down those leaf clocks which appear to be unreferenced? Indeed, that would break things. > Thirdly, the API (as I designed it) says so: > > /** > * clk_put - "free" the clock source > * @clk: clock source > * > * Note: drivers must ensure that all clk_enable calls made on this > * clock source are balanced by clk_disable calls prior to calling > * this function. > * > * clk_put should not be called from within interrupt context. > */ > void clk_put(struct clk *clk); > > which has been there since the API was first created - it's part of the > contract between drivers using the API and implementers creating something > which conforms to the API - which today means CCF. That's enough of a reason on its own :) I should have checked clk.h > The intention here is that while there are any users holding a clk_get() > reference on a clock, the clock is assumed to be required for some > device, and the struct clk may not be kfree'd, nor may its state be > changed in an unpredictable way to those drivers holding a reference > to it. I understand now, thanks for the insight. I'll talk with Maxime and get this sorted out. As a side note, should drivers/base/power/clock_ops.c be fixed too? I have added Rafael to Cc. Cheers, Emilio