[LTP] cpufreq.c: add new test for cpufreq sysfs interface validation

[linuxtestproject.agent@gmail.com]

Hi Piotr,

On Tue, 5 May 2026 13:02:09 +0200, Piotr Kubaj wrote:
> cpufreq.c: add new test for cpufreq sysfs interface validation

> +/*\
> + * Runs various sanity checks for intel_pstate cpufreq sysfs interface.
> + * ...
> + */

The doc comment does not state why root is needed. Per ground-rules rule 4,
document the reason in the doc block — e.g. "Requires root to write to
/sys/devices/system/cpu/intel_pstate/ and per-CPU cpufreq sysfs attributes."

[...]

> +	SAFE_FILE_SCANF("/sys/devices/system/cpu/intel_pstate/no_turbo", "%d", &no_turbo);
> +	SAFE_FILE_SCANF("/sys/devices/system/cpu/intel_pstate/status", "%15s", intel_pstate_status);

CONFIG_X86_INTEL_PSTATE=y does not guarantee the driver is active at runtime
(acpi_cpufreq may take over, or the driver may be in "off" mode). If the
sysfs files are absent, SAFE_FILE_SCANF calls tst_brk(TBROK). Guard with
an existence check and use tst_brk(TCONF, "intel_pstate driver not active")
instead.

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