From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nishanth Menon Subject: Re: [RFC PATCH 3/6] PM / Voltagedomain: introduce voltage domain driver support Date: Mon, 10 Mar 2014 12:11:44 -0500 Message-ID: <531DF250.5060100@ti.com> References: <1392755543-28335-1-git-send-email-nm@ti.com> <1392755543-28335-4-git-send-email-nm@ti.com> <20140224015826.GU25940@sirena.org.uk> <530B594F.2030500@ti.com> <20140303035426.GC2411@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140303035426.GC2411@sirena.org.uk> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Mark Brown Cc: devicetree@vger.kernel.org, Mike Turquette , linux-doc@vger.kernel.org, Viresh Kumar , linux-pm@vger.kernel.org, "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, cpufreq@vger.kernel.org, MyungJoo Ham , linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org On 03/02/2014 09:54 PM, Mark Brown wrote: > On Mon, Feb 24, 2014 at 08:38:07AM -0600, Nishanth Menon wrote: > >> Intent here is to allow drivers such as cpufreq-cpu0 to be reused on >> platforms such as TI's OMAP derivatives, and other SoCs which differ >> only by the sequence involved in voltage scale operations. So, this >> patch provides a framework for registering the underlying >> implementation of the SoC specific voltage change methodology. > > That bit is clear, what's very opaque from the code is how this is going > to be accomplished. The SoC specific voltage domain drivers register with devm_voltdm_register. the fops provide the abstraction needed for the SoC (example in patch #5 - which introduces OMAP specific voltage domain which handles ABB and VDD regulators). What would you suggest that we do to clarify the usage here? >> Overall the sequence takes place after this patch is as follows: >> a) voltage domain drivers such as those of TI or others register with >> voltage domain with devm_voltdm_register. >> b) cpufreq-cpu0/devfreq drivers: >> of_pm_voltdm_notifier_register(introduced as part of patch #1) to >> register notifiers around clk of interest. This request is linked to >> the specific voltage domain using phandle in device tree. >> c) when cpufreq-cpu0/devfreq does a clk_set_rate, the common clock >> framework triggers notifiers in voltage domain core which in turn, >> invokes the corresponding handlers for the voltage domain driver >> ensuring the right dvfs sequence specific to the SoC is triggered. > > So the first question I have here is what happens if multiple clocks > need to be updated in lock step - if we're only triggering off clock > notifiers that seems tricky. The other thing here is that the fact that Yes, that is true, however, there are ways to implement them, for example: We could implement an higher level clock that takes care of the multiple clock node control to handle this kind of scenario. I can elaborate that in the commit message, if that is desirable. > your API is "of_" suggests that it is in fact linked very srongly to DT > - it'd be good to split out the layers to make sure things make sense > standalone, the DT helpers are obviously good but the API should be able > to stand separately. You are correct, I had intended the RFC as purely "OF only". I will make it independent of of in the next revision. -- Regards, Nishanth Menon