From mboxrd@z Thu Jan 1 00:00:00 1970 From: skannan@codeaurora.org Subject: Re: [PATCH] PM / devfreq: Generic cpufreq governor Date: Wed, 01 Aug 2018 13:16:11 -0700 Message-ID: <07f57aced47960cf48f273d6446b4221@codeaurora.org> References: <1532750217-8886-1-git-send-email-skannan@codeaurora.org> <2a9bfa53-31b2-b44a-0bd5-07bcc344a466@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <2a9bfa53-31b2-b44a-0bd5-07bcc344a466@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Sudeep Holla Cc: MyungJoo Ham , Kyungmin Park , Chanwoo Choi , Rob Herring , Mark Rutland , linux-pm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: devicetree@vger.kernel.org On 2018-08-01 09:03, Sudeep Holla wrote: > On 28/07/18 04:56, Saravana Kannan wrote: >> Many CPU architectures have caches that can scale independent of the >> CPUs. >> Frequency scaling of the caches is necessary to make sure the cache is >> not >> a performance bottleneck that leads to poor performance and power. The >> same >> idea applies for RAM/DDR. >> >> To achieve this, this patch adds a generic devfreq governor that can >> listen >> to the frequency transitions of each CPU frequency domain and then >> adjusts >> the frequency of the cache (or any devfreq device) based on the >> frequency >> of the CPUs. >> >> To decide the frequency of the device, the governor does one of the >> following: >> >> * Uses a CPU frequency to device frequency mapping table >> - Either one mapping table used for all CPU freq policies (typically >> used >> for system with homogeneous cores/clusters that have the same >> OPPs. >> - One mapping table per CPU freq policy (typically used for ASMP >> systems >> with heterogeneous CPUs with different OPPs) >> >> OR >> >> * Scales the device frequency in proportion to the CPU frequency. So, >> if >> the CPUs are running at their max frequency, the device runs at its >> max >> frequency. If the CPUs are running at their min frequency, the >> device >> runs at its min frequency. And interpolated for frequencies in >> between. >> > > Is this solution for the old generation of SDM ? This code isn't even specific to Qualcomm chips. Let alone a specific generation of SDM. > I have seen newer ones have some kind of firmware interface/hardware to > deal with CPUFreq. Do you need this solution for them too ? You are confusing two completely unrelated drivers. This is generic *devfreq* *governor* code. I'll be renaming the commit text like Rafael suggested. Something like: CPU frequency to devfreq mapping governor. > If yes, why ? Read the commit text. > IMO firmware can arbitrate various requests for frequency > scaling and do the *right thing* for the platform. Firmware (if any) can arbitrate HW that it controls. DDR and interconnect is not something a firmware might control (or should control). > Having OSPM sending > separate requests for such bus/interconnect might end up with > conflicts. > No ? If some chips have firmware that takes care of everything, then you obviously won't be enabling any power management code. Thanks, Saravana