linux-kernel - Re: [PATCH v2 2/2] cpufreq: Specify default governor on command line

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Date:   Thu, 25 Jun 2020 17:06:02 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     rjw@...ysocki.net, rafael@...nel.org, arnd@...db.de,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        kernel-team@...roid.com, tkjos@...gle.com, adharmap@...eaurora.org
Subject: Re: [PATCH v2 2/2] cpufreq: Specify default governor on command line

After your last email (reply to my patch), I noticed a change which
isn't required. :)

On 23-06-20, 15:21, Quentin Perret wrote:
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 0128de3603df..4b1a5c0173cf 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -50,6 +50,9 @@ static LIST_HEAD(cpufreq_governor_list);
>  #define for_each_governor(__governor)				\
>  	list_for_each_entry(__governor, &cpufreq_governor_list, governor_list)
>  
> +static char cpufreq_param_governor[CPUFREQ_NAME_LEN];
> +static struct cpufreq_governor *default_governor;
> +
>  /**
>   * The "cpufreq driver" - the arch- or hardware-dependent low
>   * level driver of CPUFreq support, and its spinlock. This lock
> @@ -1055,7 +1058,6 @@ __weak struct cpufreq_governor *cpufreq_default_governor(void)
>  
>  static int cpufreq_init_policy(struct cpufreq_policy *policy)
>  {
> -	struct cpufreq_governor *def_gov = cpufreq_default_governor();
>  	struct cpufreq_governor *gov = NULL;
>  	unsigned int pol = CPUFREQ_POLICY_UNKNOWN;
>  
> @@ -1065,8 +1067,8 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy)
>  		if (gov) {
>  			pr_debug("Restoring governor %s for cpu %d\n",
>  				 policy->governor->name, policy->cpu);
> -		} else if (def_gov) {
> -			gov = def_gov;
> +		} else if (default_governor) {
> +			gov = default_governor;
>  		} else {
>  			return -ENODATA;
>  		}


> @@ -1074,8 +1076,8 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy)
>  		/* Use the default policy if there is no last_policy. */
>  		if (policy->last_policy) {
>  			pol = policy->last_policy;
> -		} else if (def_gov) {
> -			pol = cpufreq_parse_policy(def_gov->name);
> +		} else if (default_governor) {
> +			pol = cpufreq_parse_policy(default_governor->name);

This change is not right IMO. This part handles the set-policy case,
where there are no governors. Right now this code, for some reasons
unknown to me, forcefully uses the default governor set to indicate
the policy, which is not a great idea in my opinion TBH. This doesn't
and shouldn't care about governor modules and should only be looking
at strings instead of governor pointer.

Rafael, I even think we should remove this code completely and just
rely on what the driver has sent to us. Using the selected governor
for set policy drivers is very confusing and also we shouldn't be
forced to compiling any governor for the set-policy case.

-- 
viresh