linux-kernel - Re: [PATCH] cpufreq: scpi: compare against frequency instead of rate

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Message-ID: <Z5IzMhTOhtujyH0n@bogus>
Date: Thu, 23 Jan 2025 12:16:50 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: zuoqian <zuoqian113@...il.com>,
	Ionela Voinescu <ionela.voinescu@....com>, rafael@...nel.org,
	Sudeep Holla <sudeep.holla@....com>, viresh.kumar@...aro.org,
	cristian.marussi@....com, arm-scmi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: scpi: compare against frequency instead of rate

(for some reason I don't have the original email)

On Thu, Jan 23, 2025 at 02:12:14PM +0300, Dan Carpenter wrote:
> On Thu, Jan 23, 2025 at 07:53:20AM +0000, zuoqian wrote:
> > The CPU rate from clk_get_rate() may not be divisible by 1000
> > (e.g., 133333333). But the rate calculated from frequency is always
> > divisible by 1000 (e.g., 133333000).
> > Comparing the rate causes a warning during CPU scaling:
> > "cpufreq: __target_index: Failed to change cpu frequency: -5".
> > When we choose to compare frequency here, the issue does not occur.
> > 
> > Signed-off-by: zuoqian <zuoqian113@...il.com>
> > ---
> >  drivers/cpufreq/scpi-cpufreq.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/cpufreq/scpi-cpufreq.c b/drivers/cpufreq/scpi-cpufreq.c
> > index cd89c1b9832c..3bff4bb5ab4a 100644
> > --- a/drivers/cpufreq/scpi-cpufreq.c
> > +++ b/drivers/cpufreq/scpi-cpufreq.c
> > @@ -39,8 +39,9 @@ static unsigned int scpi_cpufreq_get_rate(unsigned int cpu)
> >  static int
> >  scpi_cpufreq_set_target(struct cpufreq_policy *policy, unsigned int index)
> >  {
> > -	u64 rate = policy->freq_table[index].frequency * 1000;
> 
> policy->freq_table[index].frequency is a u32 so in this original
> calculation, even though "rate" is declared as a u64, it can't actually
> be more than UINT_MAX.
>

Agreed and understood.

> > +	unsigned long freq = policy->freq_table[index].frequency;
> >  	struct scpi_data *priv = policy->driver_data;
> > +	u64 rate = freq * 1000;
>
> So you've fixed this by casting policy->freq_table[index].frequency
> to unsigned long, which fixes the problem on 64bit systems but it still
> remains on 32bit systems.  It would be better to declare freq as a u64.
>

Just trying to understand if that matters. freq is in kHz as copied
from policy->freq_table[index].frequency and we compare it with
kHZ below as the obtained clock rate is divided by 1000. What am I
missing ? If it helps, it can be renamed as freq_in_khz and even keep
it as "unsigned int" as in struct cpufreq_frequency_table.

-- 
Regards,
Sudeep