linux-kernel - Re: [Patch v3 3/6] cpufreq: qcom-cpufreq-hw: Add dcvs interrupt support

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Date:   Wed, 14 Jul 2021 08:37:19 -0400
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org, rui.zhang@...el.com,
        daniel.lezcano@...aro.org, rjw@...ysocki.net, robh+dt@...nel.org,
        tdas@...eaurora.org, mka@...omium.org,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [Patch v3 3/6] cpufreq: qcom-cpufreq-hw: Add dcvs interrupt
 support



On 7/12/21 11:18 PM, Viresh Kumar wrote:
> On 12-07-21, 21:18, Thara Gopinath wrote:
>> So I really need the interrupt to fire and then the timer to kick in and
>> take up the monitoring. I can think of introducing a variable is_disabled
>> which is updated and read under a spinlock. qcom_cpufreq_hw_cpu_exit can
>> hold the spinlock and set is_disabled to true prior to cancelling the work
>> queue or disabling the interrupt. Before re-enabling the interrupt or
>> re-queuing the work in qcom_lmh_dcvs_notify, is_disabled can be read and
>> checked.
> 
> Or you can make the lmh_dcvs_poll_work item a pointer and mark it NULL in exit,
> with proper locking etc.

Yes it could work. I will spin the next version with either this or 
introducing a new variable with locking.

> 
>> But does this problem not exist in target_index , fast_switch etc also ? One
>> cpu can be disabling and the other one can be updating the target right?
> 
> The race doesn't happen there as cpufreq_unregister_driver() takes care of
> stopping everything before removing the policy. To be more precise, governor's
> ->stop() function is responsible for making sure that frequency won't be updated
> any further.
> 

-- 
Warm Regards
Thara (She/Her/Hers)