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Date: Wed, 8 Apr 2020 11:23:01 +0530 From: Viresh Kumar <viresh.kumar@...aro.org> To: sumitg <sumitg@...dia.com> Cc: rjw@...ysocki.net, catalin.marinas@....com, will@...nel.org, thierry.reding@...il.com, jonathanh@...dia.com, talho@...dia.com, linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, bbasu@...dia.com, mperttunen@...dia.com Subject: Re: [TEGRA194_CPUFREQ Patch 2/3] cpufreq: Add Tegra194 cpufreq driver On 07-04-20, 23:48, sumitg wrote: > On 06/04/20 8:25 AM, Viresh Kumar wrote: > > On 05-04-20, 00:08, sumitg wrote: > > > On 26/03/20 5:20 PM, Viresh Kumar wrote: > > > > On 03-12-19, 23:02, Sumit Gupta wrote: > > > > > diff --git a/drivers/cpufreq/tegra194-cpufreq.c b/drivers/cpufreq/tegra194-cpufreq.c > > > > > +static unsigned int tegra194_get_speed_common(u32 cpu, u32 delay) > > > > > +{ > > > > > + struct read_counters_work read_counters_work; > > > > > + struct tegra_cpu_ctr c; > > > > > + u32 delta_refcnt; > > > > > + u32 delta_ccnt; > > > > > + u32 rate_mhz; > > > > > + > > > > > + read_counters_work.c.cpu = cpu; > > > > > + read_counters_work.c.delay = delay; > > > > > + INIT_WORK_ONSTACK(&read_counters_work.work, tegra_read_counters); > > > > > + queue_work_on(cpu, read_counters_wq, &read_counters_work.work); > > > > > + flush_work(&read_counters_work.work); > > > > > > > > Why can't this be done in current context ? > > > > > > > We used work queue instead of smp_call_function_single() to have long delay. > > > > Please explain completely, you have raised more questions than you > > answered :) > > > > Why do you want to have long delays ? > > > Long delay value is used to have the observation window long enough for > correctly reconstructing the CPU frequency considering noise. > In next patch version, changed delay value to 500us which in our tests is > considered reliable. I understand that you need to put a udelay() while reading the freq from hardware, that is fine, but why do you need a workqueue for that? Why can't you just read the values directly from the same context ? -- viresh
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