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

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Message-ID: <ad11dfc1-5e88-4421-b427-3955d4220133@stanley.mountain>
Date: Thu, 23 Jan 2025 14:12:14 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: zuoqian <zuoqian113@...il.com>,
	Ionela Voinescu <ionela.voinescu@....com>
Cc: sudeep.holla@....com, rafael@...nel.org, 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

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.

> +	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.

We keep fixing and then breaking this as undocumented parts of larger
patches.  :P  It should really be done by itself and the Fixes tag would
point to:
Fixes: 1a0419b0db46 ("cpufreq: move invariance setter calls in cpufreq core")

>  	int ret;
>  
>  	ret = clk_set_rate(priv->clk, rate);
> @@ -48,7 +49,7 @@ scpi_cpufreq_set_target(struct cpufreq_policy *policy, unsigned int index)
>  	if (ret)
>  		return ret;
>  
> -	if (clk_get_rate(priv->clk) != rate)
> +	if (clk_get_rate(priv->clk) / 1000 != freq)


Sure, I don't know this code well but your commit message seems reasonable.
Add a Fixes tag for this line.

Fixes: 343a8d17fa8d ("cpufreq: scpi: remove arm_big_little dependency")

regards,
dan carpenter