[PATCH 6.6 017/105] cpufreq: CPPC: Avoid using CPUFREQ_ETERNAL as transition delay

Greg Kroah-Hartman
2025-10-21T19:52:59Z

From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

[ Upstream commit f965d111e68f4a993cc44d487d416e3d954eea11 ]

If cppc_get_transition_latency() returns CPUFREQ_ETERNAL to indicate a
failure to retrieve the transition latency value from the platform
firmware, the CPPC cpufreq driver will use that value (converted to
microseconds) as the policy transition delay, but it is way too large
for any practical use.

Address this by making the driver use the cpufreq's default
transition latency value (in microseconds) as the transition delay
if CPUFREQ_ETERNAL is returned by cppc_get_transition_latency().

Fixes: d4f3388afd48 ("cpufreq / CPPC: Set platform specific transition_delay_us")
Cc: 5.19+ <stable@vger.kernel.org> # 5.19
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Reviewed-by: Jie Zhan <zhanjie9@hisilicon.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Qais Yousef <qyousef@layalina.io>
[ added CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS definition to include/linux/cpufreq.h ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/cpufreq/cppc_cpufreq.c | 14 ++++++++++++--
include/linux/cpufreq.h | 3 +++
2 files changed, 15 insertions(+), 2 deletions(-)

--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -344,6 +344,16 @@ static int cppc_verify_policy(struct cpu
return 0;
}

+static unsigned int __cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
+{
+ unsigned int transition_latency_ns = cppc_get_transition_latency(cpu);
+
+ if (transition_latency_ns == CPUFREQ_ETERNAL)
+ return CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS / NSEC_PER_USEC;
+
+ return transition_latency_ns / NSEC_PER_USEC;
+}
+
/*
* The PCC subspace describes the rate at which platform can accept commands
* on the shared PCC channel (including READs which do not count towards freq
@@ -366,12 +376,12 @@ static unsigned int cppc_cpufreq_get_tra
return 10000;
}
}
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#else
static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
{
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#endif

--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -32,6 +32,9 @@
*/

#define CPUFREQ_ETERNAL (-1)
+
+#define CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS NSEC_PER_MSEC
+
#define CPUFREQ_NAME_LEN 16
/* Print length for names. Extra 1 space for accommodating '\n' in prints */
#define CPUFREQ_NAME_PLEN (CPUFREQ_NAME_LEN + 1)