linux-kernel - [PATCH v3 05/18] cpufreq/amd-pstate: Overhaul locking

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Message-ID: <20250217220707.1468365-6-superm1@kernel.org>
Date: Mon, 17 Feb 2025 16:06:54 -0600
From: Mario Limonciello <superm1@...nel.org>
To: "Gautham R . Shenoy" <gautham.shenoy@....com>,
	Perry Yuan <perry.yuan@....com>
Cc: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>,
	linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
	linux-pm@...r.kernel.org (open list:CPU FREQUENCY SCALING FRAMEWORK),
	Mario Limonciello <mario.limonciello@....com>
Subject: [PATCH v3 05/18] cpufreq/amd-pstate: Overhaul locking

From: Mario Limonciello <mario.limonciello@....com>

amd_pstate_cpu_boost_update() and refresh_frequency_limits() both
update the policy state and have nothing to do with the amd-pstate
driver itself.

A global "limits" lock doesn't make sense because each CPU can have
policies changed independently.  Each time a CPU changes values they
will atomically be written to the per-CPU perf member. Drop per CPU
locking cases.

The remaining "global" driver lock is used to ensure that only one
entity can change driver modes at a given time.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
Signed-off-by: Mario Limonciello <mario.limonciello@....com>
---
 drivers/cpufreq/amd-pstate.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 5a23457a354d1..92ef2e6612a62 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -196,7 +196,6 @@ static inline int get_mode_idx_from_str(const char *str, size_t size)
 	return -EINVAL;
 }
 
-static DEFINE_MUTEX(amd_pstate_limits_lock);
 static DEFINE_MUTEX(amd_pstate_driver_lock);
 
 static u8 msr_get_epp(struct amd_cpudata *cpudata)
@@ -752,7 +751,6 @@ static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)
 		pr_err("Boost mode is not supported by this processor or SBIOS\n");
 		return -EOPNOTSUPP;
 	}
-	guard(mutex)(&amd_pstate_driver_lock);
 
 	ret = amd_pstate_cpu_boost_update(policy, state);
 	refresh_frequency_limits(policy);
@@ -1173,8 +1171,6 @@ static ssize_t store_energy_performance_preference(
 	if (ret < 0)
 		return -EINVAL;
 
-	guard(mutex)(&amd_pstate_limits_lock);
-
 	ret = amd_pstate_set_energy_pref_index(policy, ret);
 
 	return ret ? ret : count;
@@ -1347,8 +1343,10 @@ int amd_pstate_update_status(const char *buf, size_t size)
 	if (mode_idx < 0 || mode_idx >= AMD_PSTATE_MAX)
 		return -EINVAL;
 
-	if (mode_state_machine[cppc_state][mode_idx])
+	if (mode_state_machine[cppc_state][mode_idx]) {
+		guard(mutex)(&amd_pstate_driver_lock);
 		return mode_state_machine[cppc_state][mode_idx](mode_idx);
+	}
 
 	return 0;
 }
@@ -1369,7 +1367,6 @@ static ssize_t status_store(struct device *a, struct device_attribute *b,
 	char *p = memchr(buf, '\n', count);
 	int ret;
 
-	guard(mutex)(&amd_pstate_driver_lock);
 	ret = amd_pstate_update_status(buf, p ? p - buf : count);
 
 	return ret < 0 ? ret : count;
@@ -1641,8 +1638,6 @@ static int amd_pstate_epp_cpu_offline(struct cpufreq_policy *policy)
 	if (cpudata->suspended)
 		return 0;
 
-	guard(mutex)(&amd_pstate_limits_lock);
-
 	if (trace_amd_pstate_epp_perf_enabled()) {
 		trace_amd_pstate_epp_perf(cpudata->cpu, perf.highest_perf,
 					  AMD_CPPC_EPP_BALANCE_POWERSAVE,
@@ -1682,8 +1677,6 @@ static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
 	struct amd_cpudata *cpudata = policy->driver_data;
 
 	if (cpudata->suspended) {
-		guard(mutex)(&amd_pstate_limits_lock);
-
 		/* enable amd pstate from suspend state*/
 		amd_pstate_epp_reenable(policy);
 
-- 
2.43.0