From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Turquette Subject: Re: possibility of parent clock selection through DT Date: Mon, 12 Nov 2012 13:22:12 -0800 Message-ID: <20121112212212.20034.78522@nucleus> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: "devicetree-discuss" To: Shiraz Hashim , Rob Herring Cc: Viresh Kumar , devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: devicetree@vger.kernel.org Quoting Shiraz Hashim (2012-11-06 22:36:10) > On Wed, Nov 7, 2012 at 11:42 AM, Shiraz Hashim > wrote: > > Hi Mike, Rob, > > > > Devices in a SoC can have multiple possible clock sources which is > > perfectly captured through clk framework. > > > > But the device itself may not be aware of the complex hierarchy above it. > > In this case how do you suggest a board (through DT) should select its > > preference. > > > > Is there some work already going on in this direction ? > > Just to make it clear, I already have referred the clock DT bindings and > Shawn Guo patch on removing clk look up registration from kernel code. > > Here I am talking about possibility of selecting desired clock hierarchy > by the boards about which device nodes are not aware. > One way to achieve this is to use clk_set_rate as a way to switch parents at run-time. The OMAP CCF code currently does this when relocking PLLs and makes use of __clk_reparent to update the clock framework's representation of the hierarchy dynamically. Maybe something like the following is helpful to you: http://git.linaro.org/gitweb?p=people/mturquette/linux.git;a=blob;f=arch/arm/mach-omap2/dpll3xxx.c;h=f72dedb4eee892ce4cd5bdf22cc8c22510f3d526;hb=clk-omap-3.8#l542 Regards, Mike > -- > regards > Shiraz Hashim