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cpufreq: Fail driver register if it has adjust_perf without fast_switch

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If fast_switch_possible flag is set by the scaling driver, the governor
is free to select fast_switch function even if adjust_perf is set.  Some
scaling drivers which use adjust_perf don't set fast_switch thinking
that the governor would never fall back to fast_switch. But the governor
can fall back to fast_switch even in runtime if frequency invariance is
disabled due to some reason. This could crash the kernel if the driver
didn't set the fast_switch function pointer.

Therefore, fail driver registration if it has adjust_perf without
fast_switch.

Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Suggested-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Wyes Karny <wyes.karny@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Wyes Karny
2023-05-29 14:25:51 +00:00
committed by Rafael J. Wysocki
parent 858fd168a9
commit b4a11fa333
2 changed files with 6 additions and 2 deletions
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5
include/linux/cpufreq.h
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@@ -340,7 +340,10 @@ struct cpufreq_driver {
/*
* ->fast_switch() replacement for drivers that use an internal
* representation of performance levels and can pass hints other than
* the target performance level to the hardware.
* the target performance level to the hardware. This can only be set
* if ->fast_switch is set too, because in those cases (under specific
* conditions) scale invariance can be disabled, which causes the
* schedutil governor to fall back to the latter.
*/
void (*adjust_perf)(unsigned int cpu,
unsigned long min_perf,