linux-kernel - [PATCH 08/14] cpufreq/amd-pstate: Cache CPPC request in shared mem case too

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Message-ID: <20250206215659.3350066-9-superm1@kernel.org>
Date: Thu,  6 Feb 2025 15:56:53 -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 08/14] cpufreq/amd-pstate: Cache CPPC request in shared mem case too

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

In order to prevent a potential write for shmem_update_perf()
cache the request into the cppc_req_cached variable normally only
used for the MSR case.

This adds symmetry into the code and potentially avoids extra writes.

Signed-off-by: Mario Limonciello <mario.limonciello@....com>
---
 drivers/cpufreq/amd-pstate.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index cd96443fc117f..2aa3d5be2efe5 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -502,6 +502,8 @@ static int shmem_update_perf(struct amd_cpudata *cpudata, u8 min_perf,
 			     u8 des_perf, u8 max_perf, u8 epp, bool fast_switch)
 {
 	struct cppc_perf_ctrls perf_ctrls;
+	u64 value, prev;
+	int ret;
 
 	if (cppc_state == AMD_PSTATE_ACTIVE) {
 		int ret = shmem_set_epp(cpudata, epp);
@@ -510,11 +512,29 @@ static int shmem_update_perf(struct amd_cpudata *cpudata, u8 min_perf,
 			return ret;
 	}
 
+	value = prev = READ_ONCE(cpudata->cppc_req_cached);
+
+	value &= ~(AMD_CPPC_MAX_PERF_MASK | AMD_CPPC_MIN_PERF_MASK |
+		   AMD_CPPC_DES_PERF_MASK | AMD_CPPC_EPP_PERF_MASK);
+	value |= FIELD_PREP(AMD_CPPC_MAX_PERF_MASK, max_perf);
+	value |= FIELD_PREP(AMD_CPPC_DES_PERF_MASK, des_perf);
+	value |= FIELD_PREP(AMD_CPPC_MIN_PERF_MASK, min_perf);
+	value |= FIELD_PREP(AMD_CPPC_EPP_PERF_MASK, epp);
+
+	if (value == prev)
+		return 0;
+
 	perf_ctrls.max_perf = max_perf;
 	perf_ctrls.min_perf = min_perf;
 	perf_ctrls.desired_perf = des_perf;
 
-	return cppc_set_perf(cpudata->cpu, &perf_ctrls);
+	ret = cppc_set_perf(cpudata->cpu, &perf_ctrls);
+	if (ret)
+		return ret;
+
+	WRITE_ONCE(cpudata->cppc_req_cached, value);
+
+	return 0;
 }
 
 static inline bool amd_pstate_sample(struct amd_cpudata *cpudata)
-- 
2.43.0