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Message-ID: <20230529142551.6726-1-wyes.karny@amd.com>
Date: Mon, 29 May 2023 14:25:51 +0000
From: Wyes Karny <wyes.karny@....com>
To: <rafael@...nel.org>, <viresh.kumar@...aro.org>
CC: <ray.huang@....com>, <linux-pm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <gautham.shenoy@....com>,
Wyes Karny <wyes.karny@....com>
Subject: [PATCH v4.1] cpufreq: Fail driver register if it has adjust_perf without fast_switch
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@...nel.org>
Suggested-by: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Wyes Karny <wyes.karny@....com>
---
drivers/cpufreq/cpufreq.c | 3 ++-
include/linux/cpufreq.h | 5 ++++-
2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 6b52ebe5a890..50bbc969ffe5 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2828,7 +2828,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
(driver_data->setpolicy && (driver_data->target_index ||
driver_data->target)) ||
(!driver_data->get_intermediate != !driver_data->target_intermediate) ||
- (!driver_data->online != !driver_data->offline))
+ (!driver_data->online != !driver_data->offline) ||
+ (driver_data->adjust_perf && !driver_data->fast_switch))
return -EINVAL;
pr_debug("trying to register driver %s\n", driver_data->name);
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 26e2eb399484..172ff51c1b2a 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -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,
--
2.34.1
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