Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754317Ab1DUP6F (ORCPT ); Thu, 21 Apr 2011 11:58:05 -0400 Received: from imr4.ericy.com ([198.24.6.8]:46331 "EHLO imr4.ericy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750915Ab1DUP6D (ORCPT ); Thu, 21 Apr 2011 11:58:03 -0400 Date: Thu, 21 Apr 2011 08:56:58 -0700 From: Guenter Roeck To: Arnd Bergmann CC: "Hans J. Koch" , Greg Kroah-Hartman , Andrew Morton , Jonathan Cameron , Randy Dunlap , "linux-doc@vger.kernel.org" , "linux-i2c@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] misc: Driver for Silicon Labs Si570 and compatibles Message-ID: <20110421155658.GA28245@ericsson.com> References: <1303248968-5069-1-git-send-email-guenter.roeck@ericsson.com> <201104201844.30919.arnd@arndb.de> <20110420181652.GA23298@ericsson.com> <201104211311.25988.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <201104211311.25988.arnd@arndb.de> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3028 Lines: 62 On Thu, Apr 21, 2011 at 07:11:25AM -0400, Arnd Bergmann wrote: > On Wednesday 20 April 2011, Guenter Roeck wrote: > > On Wed, Apr 20, 2011 at 12:44:30PM -0400, Arnd Bergmann wrote: > > > On Tuesday 19 April 2011, Guenter Roeck wrote: > > > > This driver adds support for Si570, Si571, Si598, and Si599 > > > > programmable XO/VCXO. > > > > > > > > Signed-off-by: Guenter Roeck > > > > > > This needs some more explanation of what the hardware is there for, > > > and why it's unlike everything else that we support in Linux. > > > > > This is a generic configurable clock device. I'll be happy to add > > some text such as "The device can be used for any application requiring > > a static or a dynamically configurable clock, such as serdes clocks". > > Not sure if that would add much value, though. > > > > Regarding "unlike everything else", not sure if that is really correct. > > The DDS chips Jonathan mentioned do get pretty close, and there are > > other drivers providing support for clock chips, though typically more > > dedicated. ics932s401 in misc is one example, and then there are all > > the tuner chips in media/common/tuners/. > > Isn't that what you'd normally call a 'struct clk' then? > Yes, it would be nice to have that as part of the kernel and not architecture specific. > > > If that is true, it should probably not have a user-visible > > > interface, but only an interface that can be used by other > > > kernel drivers. > > > > > Depends. In our case, turns out the devices consuming the clock > > have user mode drivers. Lots of history there, but the chip vendors > > provide those user mode drivers, and the teams responsible for > > integrating the drivers decided to not rewrite it to kernel mode drivers. > > Also, for special purposes such as margining, it is necessary to control > > the clock from userspace. So, for our use case, I need the user-visible > > interface. I _don't_ need the kernel interface, at least not right now, > > which is why I did not add it. > > > > Browsing through the web, it seems the chip is somewhat popular with > > Amateur Radio. No idea if it would ever be controlled for such a purpose > > from Linux, but if so, it would also require a user configurable frequency. > > > > If there is a better place for such a driver than misc, please let me know. > > When you say user mode driver, do you mean as in drivers/uio? (taking Hans > on Cc for these) > > Those already have generic support for memory and interrupt resources, > maybe we can just add a common way to associate a uio device with a struct clk > and provide a sysfs or ioctl interface to set a clock for a given device. > ... and provide the clk infrastructure for x86, which is where I need it. Guenter -- 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/