Hi Viresh,
On 14/07/2020 04:46, Viresh Kumar wrote:
...
> The get() callback is supposed to read the frequency from hardware and
> return it, no cached value here. policy->cur may end up being wrong in
> case there is a bug.
I have been doing some more testing on Tegra, I noticed that when
reading the current CPU frequency via the sysfs scaling_cur_freq entry,
this always returns the cached value (at least for Tegra). Looking at
the implementation of scaling_cur_freq I see ...
static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
{
ssize_t ret;
unsigned int freq;
freq = arch_freq_get_on_cpu(policy->cpu);
if (freq)
ret = sprintf(buf, "%u\n", freq);
else if (cpufreq_driver && cpufreq_driver->setpolicy &&
cpufreq_driver->get)
ret = sprintf(buf, "%u\n", cpufreq_driver->get(policy->cpu));
else
ret = sprintf(buf, "%u\n", policy->cur);
return ret;
}
The various Tegra CPU frequency drivers do not implement the
set_policy callback and hence why we always get the cached value. I
see the following commit added this and before it simply return the
cached value ...
commit c034b02e213d271b98c45c4a7b54af8f69aaac1e
Author: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
Date: Mon Oct 13 08:37:40 2014 -0700
cpufreq: expose scaling_cur_freq sysfs file for set_policy() drivers
Is this intentional?
Cheers
Jon
--
nvpublic
