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Date: Tue, 10 Aug 2021 14:25:15 +0100 From: Lukasz Luba <lukasz.luba@....com> To: Quentin Perret <qperret@...gle.com> Cc: Viresh Kumar <viresh.kumar@...aro.org>, Rafael Wysocki <rjw@...ysocki.net>, Vincent Donnefort <vincent.donnefort@....com>, Andy Gross <agross@...nel.org>, Bjorn Andersson <bjorn.andersson@...aro.org>, Cristian Marussi <cristian.marussi@....com>, Fabio Estevam <festevam@...il.com>, Kevin Hilman <khilman@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>, NXP Linux Team <linux-imx@....com>, Pengutronix Kernel Team <kernel@...gutronix.de>, Sascha Hauer <s.hauer@...gutronix.de>, Shawn Guo <shawnguo@...nel.org>, Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org, Vincent Guittot <vincent.guittot@...aro.org>, linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org, linux-omap@...r.kernel.org Subject: Re: [PATCH 0/8] cpufreq: Auto-register with energy model On 8/10/21 1:35 PM, Quentin Perret wrote: > On Tuesday 10 Aug 2021 at 13:06:47 (+0530), Viresh Kumar wrote: >> Provide a cpufreq driver flag so drivers can ask the cpufreq core to register >> with the EM core on their behalf. > > Hmm, that's not quite what this does. This asks the cpufreq core to > use *PM_OPP* to register an EM, which I think is kinda wrong to do from > there IMO. The decision to use PM_OPP or another mechanism to register > an EM belongs to platform specific code (drivers), so it is odd for the > PM_OPP registration to have its own cpufreq flag but not the other ways. > > As mentioned in another thread, the very reason to have PM_EM is to not > depend on PM_OPP, so I'm worried about the direction of travel with this > series TBH. > >> This allows us to get rid of duplicated code >> in the drivers and fix the unregistration part as well, which none of the >> drivers have done until now. > > This series adds more code than it removes, and the unregistration is > not a fix as we don't ever remove the EM tables by design, so not sure > either of these points are valid arguments. > >> This would also make the registration with EM core to happen only after policy >> is fully initialized, and the EM core can do other stuff from in there, like >> marking frequencies as inefficient (WIP). Though this patchset is useful without >> that work being done and should be merged nevertheless. >> >> This doesn't update scmi cpufreq driver for now as it is a special case and need >> to be handled differently. Though we can make it work with this if required. > > Note that we'll have more 'special cases' if other architectures start > using PM_EM, which is what we have been trying to allow since the > beginning, so that's worth keeping in mind. > The way I see this is that the flag in cpufreq avoids mistakes potentially made by driver developer. It will automaticaly register the *simple* EM model via dev_pm_opp_of_register_em() on behalf of drivers (which is already done manually by drivers). The developer would just set the flag similarly to CPUFREQ_IS_COOLING_DEV and be sure it will register at the right time. Well tested flag approach should be safer, easier to understand, maintain. If there is a need for *advanced* EM model, driver developer would have to care about all these things (order, setup-ready-structures, fw channels, freeing, etc) while developing custom registration. The developer won't set this flag in such case, so the core won't try to auto register the EM for that driver. I don't see the dependency of PM_EM on PM_OPP in this series.
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