Messages in this thread Patch in this message | | | From | Wyes Karny <> | Subject | [PATCH v4 3/3] cpufreq: Return failure if fast_switch is not set and fast_switch_possible is set | Date | Wed, 17 May 2023 16:28:17 +0000 |
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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, return failure in cpufreq_online function if fast_switch is not set and fast_switch_possible is set.
Signed-off-by: Wyes Karny <wyes.karny@amd.com> --- drivers/cpufreq/cpufreq.c | 5 +++++ include/linux/cpufreq.h | 4 +++- 2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 6b52ebe5a890..7835ba4fa34c 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1376,6 +1376,11 @@ static int cpufreq_online(unsigned int cpu) goto out_free_policy; } + if (policy->fast_switch_possible && !cpufreq_driver->fast_switch) { + pr_err("fast_switch_possible is enabled but fast_switch callback is not set\n"); + ret = -EINVAL; + goto out_destroy_policy; + } /* * The initialization has succeeded and the policy is online. * If there is a problem with its frequency table, take it diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 26e2eb399484..8cdf77bb3bc1 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -340,7 +340,9 @@ 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. If driver is setting this, + * then it needs to set fast_switch also. Because in certain scenario scale + * invariance could be disabled and governor can switch back to fast_switch. */ void (*adjust_perf)(unsigned int cpu, unsigned long min_perf, -- 2.34.1
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