On Wed, 2022-04-27 at 08:41 +0530, Viresh Kumar wrote: > On 26-04-22, 19:13, Rex-BC Chen wrote: > > We have a non-upstream driver which tries to get frequency by > > 'cpufreq_get'. > > This is the right thing to do there. > > > When we use that non-upstream driver, 'cpufreq_verify_current_freq' > > will be further invoked by 'cpufreq_get' and it would cause voltage > > pulse issue as I described previously. > > I see this will eventually resolve to __cpufreq_driver_target(), > which > should return without any frequency updates. > Hello Viresh, Yes, the call stack will eventually go to __cpufreq_driver_target. However, we can observe the mismatch between target_freq and policy-cur with a tiny difference. e.g. [ 553.065356] cpufreq: target for CPU 0: 500000 kHz, relation 0, requested 500000 kHz [ 553.066366] cpufreq: target_freq/policy->cur: 500000/499999 kHz We check the assignment of policy->cur could be either from cpufreq_driver->get_intermediate or from cpufreq_driver->get. But it is strange to have the frequency value like 499999 kHz. Is the result of tiny frequency difference expected from your point of view? > What do you mean by "voltage pulse" here? What actually happens which > you want to avoid. > When cpufreq is fixed to lowest opp, "voltage pulse" is a quick voltage rising and falling phenomenon which can be observed if 'cpufreq_get' is invoked. >From top of view, if 'cpufreq_get' is NOT invoked in that condition, the voltage pulse will no longer occur. That's why we add this patch for this series. > > Therefore, we apply the solution in this series. > > I won't call it a solution but a Bug as .get() is supposed to read > real freq of the hardware. > > > Recently, we found that using 'cpufreq_generic_get' directly in our > > non-upstream driver can do the same thing without pulse issue. > > That would be an abuse of the cpufreq_generic_get() API. It is ONLY > allowed to be used while setting .get callback in the driver. > Thank you for sharing the correct information. Is it possible to get frequency (API) a simple way, like get current opp frequency? BRs, Rex
