linux-kernel - Re: [PATCH] cpufreq: Fix initialization with disabled boost

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Message-ID: <9710acf3-9ffd-4b29-a51a-21d91cbbdf5e@arm.com>
Date: Tue, 17 Jun 2025 13:56:38 +0100
From: Robin Murphy <robin.murphy@....com>
To: Christian Loehle <christian.loehle@....com>,
 "zhenglifeng (A)" <zhenglifeng1@...wei.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 linux-pm <linux-pm@...r.kernel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH] cpufreq: Fix initialization with disabled boost

On 17/06/2025 9:20 am, Christian Loehle wrote:
> On 6/17/25 03:14, zhenglifeng (A) wrote:
>> On 2025/6/17 3:10, Robin Murphy wrote:
>>> On 2025-06-16 6:25 pm, Christian Loehle wrote:
>>>> The boost_enabled early return in policy_set_boost() caused
>>>> the boost disabled at initialization to not actually set the
>>>> initial policy->max, therefore effectively enabling boost while
>>>> it should have been enabled.
>>>>
>>>> Fixes: 27241c8b63bd ("cpufreq: Introduce policy_set_boost()")
>>>
>>> I think it's a bit older than that - I noticed this with 6.15 stable, prior to that refactoring, and from a poke through the history the underlying logic appears to date back to dd016f379ebc ("cpufreq: Introduce a more generic way to set default per-policy boost flag"). Hopefully someone can figure out the appropriate stable backport.
>>>
>>> I can at least confirm that equivalently hacking out the "&& policy->boost_enabled != cpufreq_boost_enabled()" condition previously here does have the desired effect for me of initialising scaling_max_freq correctly at boot, but I'm not sure that's entirely correct on its own...
>>>
>>> Thanks,
>>> Robin.
>>>
>>>> Reported-by: Robin Murphy <robin.murphy@....com>
>>>> Signed-off-by: Christian Loehle <christian.loehle@....com>
>>>> ---
>>>>    drivers/cpufreq/cpufreq.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>>>> index d7426e1d8bdd..e85139bd0436 100644
>>>> --- a/drivers/cpufreq/cpufreq.c
>>>> +++ b/drivers/cpufreq/cpufreq.c
>>>> @@ -1630,7 +1630,7 @@ static int cpufreq_online(unsigned int cpu)
>>>>         */
>>>>        if (cpufreq_driver->set_boost && policy->boost_supported &&
>>>>            (new_policy || !cpufreq_boost_enabled())) {
>>>> -        ret = policy_set_boost(policy, cpufreq_boost_enabled());
>>>> +        ret = cpufreq_driver->set_boost(policy, cpufreq_boost_enabled());
>>>>            if (ret) {
>>>>                /* If the set_boost fails, the online operation is not affected */
>>>>                pr_info("%s: CPU%d: Cannot %s BOOST\n", __func__, policy->cpu,
>>>
>>>
>>
>> I don't quite understand what problem you've met. It semms like you guys
>> propose that set_boost() should be called no matter what
>> policy->boost_enabled is. Having more details would help to clarify things,
>> such as which driver you use and what you expect but not be achieved.
>>
> 
> so calling policy_set_boost(policy, enable) is a noop here if
> policy->boost_enabled == cpufreq_boost_enabled():
> 
> 	if (policy->boost_enabled == enable)
> 		return 0;
> 
> We have policy->boost_enabled == false on boot, thus never actually
> setting policy->max up ever, which leads to the following:

And for clarity, this is with the cpufreq_dt driver (at least in my case).

Thanks,
Robin.

> # cat /sys/devices/system/cpu/cpufreq/policy4/scaling_boost_frequencies
> 2016000
> # cat /sys/devices/system/cpu/cpufreq/policy4/scaling_max_freq
> 2016000
> # cat /sys/devices/system/cpu/cpufreq/boost
> 0
> # echo 1 > /sys/devices/system/cpu/cpufreq/boost
> # echo 0 > /sys/devices/system/cpu/cpufreq/boost
> # cat /sys/devices/system/cpu/cpufreq/policy4/scaling_boost_frequencies
> 1800000
> 
> Anyway I'll bisect some more to find the actual first bad commit and
> resend.