Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933758Ab3CSITM (ORCPT ); Tue, 19 Mar 2013 04:19:12 -0400 Received: from mail-ee0-f49.google.com ([74.125.83.49]:63712 "EHLO mail-ee0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932203Ab3CSITJ (ORCPT ); Tue, 19 Mar 2013 04:19:09 -0400 Message-ID: <51481F79.40304@gmail.com> Date: Tue, 19 Mar 2013 09:19:05 +0100 From: Sebastian Hesselbarth User-Agent: Mozilla/5.0 (X11; Linux i686; rv:10.0.12) Gecko/20130116 Icedove/10.0.12 MIME-Version: 1.0 To: Mike Turquette CC: Arnd Bergmann , linux-doc@vger.kernel.org, Linus Walleij , linux-kernel@vger.kernel.org, Rob Herring , Grant Likely , Rob Landley , Andrew Morton , devicetree-discuss@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] clk: add DT test clock consumer driver References: <1363439376-21294-1-git-send-email-sebastian.hesselbarth@gmail.com> <201303161456.54246.arnd@arndb.de> <20130319015425.8663.84827@quantum> In-Reply-To: <20130319015425.8663.84827@quantum> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3124 Lines: 71 On 03/19/2013 02:54 AM, Mike Turquette wrote: > Quoting Arnd Bergmann (2013-03-16 07:56:54) >> On Saturday 16 March 2013, Sebastian Hesselbarth wrote: >>> This driver adds a DT test clock consumer that exposes debugfs files to >>> enable/disable and set/get rate of the attached programmable clock. >>> During development of a i2c-attached clock generator I found it useful >>> to debug the clock generator's internal pll settings by enforcing clock >>> rates through debugfs. >>> >>> Signed-off-by: Sebastian Hesselbarth >> >> It sounds a little clumsy to have a device driver to match a device that >> you create just for matching the driver. >> >> Would it be possible to separate the debugging logic from the platform >> device logic? I think it may be useful to have a debugfs or sysfs >> inteface for all clocks in the system, even if that is disabled by >> default or only available after manually loading a module implementing >> that functionality. >> > > I agree that a generic approach is needed here. I have been meaning to > break the existing debugfs stuff out into clk-debug.c. I'll do that > soon and maybe you can add a new Kconfig entry for > COMMON_CLK_DEBUG_USERSPACE (or something like that) which implements > this? Mike, I agree with you and Arnd about clumsiness and a generic approach, but this driver is a little different from controlling _all_ clocks within the tree. It just adds one consumer that can _request_ a new rate. Nevertheless, I can have a look at clk-debug and adding the functionality. > On the other hand this sort of stuff really scares me. I know for a > fact that a debug interface to enable/disable clocks and set clock rate > would ship on real devices. Quite likely some android phones out there > would be controlling hardware clocks from some horrible userspace > utility. > > *shudder* This will happen for sure. > Sebastian, another small nitpick, can you change the "enable" attribute > to be named "prepare_enable"? This more accurately reflects what is > going on. On a generic approach I would rather have a look at the actual ops that are provided and name the files accordingly. That will also allow us _not_ to set the rate of crystal oscillators ;) > I also wonder how simple it would be to add a "parent" attribute here > that allows one to call clk_set_parent from the debugfs interface? To > make it easy on you, the interface could accept an integer as the index > of the clk->parents[] array. This is a bad interface design as it > requires the user to look into the code to know which index corresponds > to which parent clock; however I do not want people to use this > interface for anything other than debug/testing, so I am ok with this > interface being a PITA to use. Sure, but it will not help much against userspace hardware clock utilities ;) Sebastian -- 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/