michael/linux
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

cpufreq: CPPC: Avoid using CPUFREQ_ETERNAL as transition delay

Browse Source 
[ Upstream commit f965d111e6 ]

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: d4f3388afd ("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>
This commit is contained in:
Rafael J. Wysocki
2025-10-18 12:25:19 -04:00
committed by Greg Kroah-Hartman
parent 59a6e61863
commit e19e401b05
2 changed files with 15 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
drivers/cpufreq/cppc_cpufreq.c
View File

@@ -344,6 +344,16 @@ static int cppc_verify_policy(struct cpufreq_policy_data *policy)
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_transition_delay_us(unsigned int cpu)
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

3
include/linux/cpufreq.h
View File

@@ -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)