[PATCH] cpufreq: CPPC: Set CPPC Enable register in cpu_init

[Sumit Gupta]

As per ACPI 6.x s8.4.6.1.4 (CPPC Enable register):
  "If supported by the platform, OSPM writes a one to this register
   to enable CPPC on this processor. If not implemented, OSPM assumes
   the platform always has CPPC enabled."

The driver never writes this register. Call cppc_set_enable() at the
start of cppc_cpufreq_cpu_init(). Errors are logged but not fatal, as
the register is optional.

Fixes: 5477fb3bd1e8 ("ACPI / CPPC: Add a CPUFreq driver for use with CPPC")
Cc: stable@xxxxxxxxxxxxxxx # v6.16+
Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
---
Sending this separately from the autonomous mode boot parameter series
where it was patch 1/2, as it is an independent bug fix.
v5 of the series:
 https://lore.kernel.org/lkml/20260623080652.3353386-1-sumitg@xxxxxxxxxx/

 drivers/cpufreq/cppc_cpufreq.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 957fa7775260..b8f4399b6e0b 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -679,6 +679,14 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	caps = &cpu_data->perf_caps;
 	policy->driver_data = cpu_data;
 
+	/*
+	 * Enable CPPC. The Enable register is optional - some platforms
+	 * may not support it.
+	 */
+	ret = cppc_set_enable(cpu, true);
+	if (ret && ret != -EOPNOTSUPP)
+		pr_warn("Failed to enable CPPC for CPU%u (%d)\n", cpu, ret);
+
 	/*
 	 * Set min to lowest nonlinear perf to avoid any efficiency penalty (see
 	 * Section 8.4.7.1.1.5 of ACPI 6.1 spec)
-- 
2.34.1