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cpufreq: CPPC: Mark driver with NEED_UPDATE_LIMITS flag

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[ Upstream commit 0a1416a49e63c320f6e6c1c8d07e1b58c0d4a3f3 ]

AMU counters on certain CPPC-based platforms tend to yield inaccurate
delivered performance measurements on systems that are idle/mostly idle.
This results in an inaccurate frequency being stored by cpufreq in its
policy structure when the CPU is brought online. [1]

Consequently, if the userspace governor tries to set the frequency to a
new value, there is a possibility that it would be the erroneous value
stored earlier. In such a scenario, cpufreq would assume that the
requested frequency has already been set and return early, resulting in
the correct/new frequency request never making it to the hardware.

Since the operating frequency is liable to this sort of inconsistency,
mark the CPPC driver with CPUFREQ_NEED_UPDATE_LIMITS so that it is always
invoked when a target frequency update is requested.

Link: https://lore.kernel.org/linux-pm/20250619000925.415528-3-pmalani@google.com/ [1]
Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Prashant Malani <pmalani@google.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://patch.msgid.link/20250722055611.130574-2-pmalani@google.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Prashant Malani
2025-07-22 05:55:40 +00:00
committed by Greg Kroah-Hartman
parent 00993cf671
commit 9415dd68c2
1 changed files with 1 additions and 1 deletions
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2
drivers/cpufreq/cppc_cpufreq.c
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@@ -396,7 +396,7 @@ static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)
}
static struct cpufreq_driver cppc_cpufreq_driver = {
.flags = CPUFREQ_CONST_LOOPS,
.flags = CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
.verify = cppc_verify_policy,
.target = cppc_cpufreq_set_target,
.get = cppc_cpufreq_get_rate,