linux-kernel - Re: [RFC PATCH] cpufreq: userspace: make scaling_setspeed return the actual requested frequency

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Message-ID: <CAJZ5v0g+TzQN6AxejRHkrmpWiuKqOLZJ4WJSjxvPpGQELZAdsA@mail.gmail.com>
Date: Wed, 28 Jan 2026 22:27:36 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>, Pengjie Zhang <zhangpengjie2@...wei.com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	zhanjie9@...ilicon.com, zhenglifeng1@...wei.com, lihuisong@...wei.com, 
	yubowen8@...wei.com, linhongye@...artners.com, linuxarm@...wei.com, 
	jonathan.cameron@...wei.com, wangzhi12@...wei.com
Subject: Re: [RFC PATCH] cpufreq: userspace: make scaling_setspeed return the
 actual requested frequency

On Mon, Jan 19, 2026 at 9:28 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 16-01-26, 17:46, Pengjie Zhang wrote:
> > According to the Linux kernel ABI documentation for 'scaling_setspeed':
> >   "It returns the last frequency requested by the governor (in kHz) or
> >    can be written to in order to set a new frequency for the policy."
> >
> > However, the current implementation of show_speed() returns 'policy->cur'.
> > 'policy->cur' represents the frequency after the driver has
> > resolved the request against the hardware frequency table and applied
> > policy limits (min/max).
> >
> > This creates a discrepancy between the documentation/user expectation and
> > the actual code behavior. For instance:
> >
> > 1. User writes a value to 'scaling_setspeed' that is not in the OPP table
> >    (e.g., user asks for A, driver rounds it to B).
> > 2. User reads 'scaling_setspeed'.
> > 3. Code returns B ('policy->cur').
> > 4. User expects A (the "frequency requested"), but gets B.
> >
> > This patch changes show_speed() to return 'userspace->setspeed', which
> > stores the actual value last requested by the user. This restores the
> > read/write symmetry of the attribute and aligns the code with the ABI
> > description.
> >
> > The effective frequency can still be observed via 'scaling_cur_freq' or
> > 'cpuinfo_cur_freq', preserving the distinction between "what was
> > requested" (setspeed) and "what is effective" (cur_freq).
> >
> > Signed-off-by: Pengjie Zhang <zhangpengjie2@...wei.com>
> > ---
> >  drivers/cpufreq/cpufreq_userspace.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq_userspace.c b/drivers/cpufreq/cpufreq_userspace.c
> > index 77d62152cd38..4bd62e6c5c51 100644
> > --- a/drivers/cpufreq/cpufreq_userspace.c
> > +++ b/drivers/cpufreq/cpufreq_userspace.c
> > @@ -49,7 +49,9 @@ static int cpufreq_set(struct cpufreq_policy *policy, unsigned int freq)
> >
> >  static ssize_t show_speed(struct cpufreq_policy *policy, char *buf)
> >  {
> > -     return sprintf(buf, "%u\n", policy->cur);
> > +     struct userspace_policy *userspace = policy->governor_data;
> > +
> > +     return sprintf(buf, "%u\n", userspace->setspeed);
> >  }
> >
> >  static int cpufreq_userspace_policy_init(struct cpufreq_policy *policy)
>
> Looks okay to me.
>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Applied as 6.20 material, thanks!