linux-kernel - Re: [PATCH v2 3/3] cpufreq: Update set_boost callbacks to rely on boost_freq

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Message-ID: <ea9111b5-cd85-4526-a959-54d8037d6ffb@huawei.com>
Date: Tue, 23 Dec 2025 16:15:34 +0800
From: "zhenglifeng (A)" <zhenglifeng1@...wei.com>
To: Pierre Gondois <pierre.gondois@....com>
CC: <linux-kernel@...r.kernel.org>, Christian Loehle
	<christian.loehle@....com>, Ionela Voinescu <ionela.voinescu@....com>, Jie
 Zhan <zhanjie9@...ilicon.com>, Huang Rui <ray.huang@....com>, "Gautham R.
 Shenoy" <gautham.shenoy@....com>, Mario Limonciello
	<mario.limonciello@....com>, Perry Yuan <perry.yuan@....com>, "Rafael J.
 Wysocki" <rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
	<linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] cpufreq: Update set_boost callbacks to rely on
 boost_freq_req

On 2025/12/18 0:22, Pierre Gondois wrote:
> cpufreq_frequency_table_cpuinfo() can effectively update
> policy->cpuinfo.max_freq, but directly setting policy->max should be wrong
> as it bypasses the other QoS constraints on the maximal frequency.
> 
> Updates to policy->max should go through the following call chain
> to be sure all constraints/notifiers are respected/called.
> freq_qos_update_request()
> \-freq_qos_apply()
>   \-pm_qos_update_target()
>     \-blocking_notifier_call_chain()
>       \-cpufreq_notifier_max()
>         \-handle_update()
>           \-refresh_frequency_limits()
>             \-cpufreq_set_policy()
> 
> FYIU, we should have:
> - max_freq_req: the maximal frequency constraint as set by the user.
>   It is updated whenever the user write to scaling_max_freq.
> - boost_freq_req: the maximal frequency constraint as set by the
>   driver. It is updated whenever boost is enabled/disabled.
> - policy->cpuinfo.max_freq: the maximal frequency reachable by the driver.
>   This value is used in cpufreq at various places to check frequencies
>   are within valid boundaries.
> - policy->max: the maximal frequency cpufreq can use. It is a resultant
>   of all the QoS constraints received (from the user, boost, thermal).
>   It should be updated whenever one of the QoS constraint is updated.
>   It should never be set directly to avoid bypassing the QoS constraints.
> 
> Whenever a cpufreq driver is initialized, policy->max is set, but the
> value is overridden whenever the user writes to scaling_max_freq.
> Thus we might think it should be replaced with a max_freq_req constraint.
> 
> However if boost is enabled, the maximal frequency will be limited by
> max_freq_req. So at init, cpufreq drivers should set boost_freq_req
> instead (to policy->cpuinfo.max_freql).
> That way, if boost is enabled, the maximal frequency available is the
> boost frequency.
> 
> ------
> 
> Summary:
> -
> policy->max should never be set directly. It should only be set through
> cpufreq_set_policy(). cpufreq_set_policy() might be called indirectly
> after updating a QoS constraint using freq_qos_update_request().
> 
> -
> boost_freq_req should be set for all cpufreq drivers, with a default value
> of policy->cpuinfo.max_freq. This represents the maximal frequency available
> with/without boost.
> Note: the name "boost_freq_req" might not be well chosen.
> 
> -
> Any update to policy->cpuinfo.max_freq should be followed by a call to
> freq_qos_update_request(policy->boost_freq_req).
> This will allow to update "policy->max" with the new boost frequency.
> 

Hi Pierre,

I now think we might not need to add a new QoS constraints. Calling
refresh_frequency_limits() instead of freq_qos_update_request() when
setting boost might solve your problem, since cpuinfo.max_freq is already
used to limit policy->max in cpufreq_set_policy().

What do you think?