[PATCH v3 2/2] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported

[Mario Limonciello]

commit 72f2ecb7ece7 ("ACPI: bus: Set CPPC _OSC bits for all and
when CPPC_LIB is supported") added support for claiming to
support CPPC in _OSC on non-Intel platforms.

This unfortunately caused a regression on a vartiety of AMD
platforms in the field because a number of AMD platforms don't set
the `_OSC` bit 5 or 6 to indicate CPPC or CPPC v2 support.

As these AMD platforms already claim CPPC support via a dedicated
MSR from `X86_FEATURE_CPPC`, use this enable this feature rather
than requiring the `_OSC` on platforms with a dedicated MSR.

If there is additional breakage on the shared memory designs also
missing this _OSC, additional follow up changes may be needed.

Fixes: 72f2ecb7ece7 ("Set CPPC _OSC bits for all and when CPPC_LIB is supported")
Reported-by: Perry Yuan <perry.yuan@xxxxxxx>
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
v2->v3
 * Rebase on top of solution for _CPC regression on some Intel systemss
 * Refactor to avoid #ifdef CONFIG_X86

 arch/x86/kernel/acpi/cppc.c |  5 +++++
 drivers/acpi/cppc_acpi.c    | 16 +++++++++++++++-
 include/acpi/cppc_acpi.h    |  1 +
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
index 8b8cbf22461a4..20e257db50740 100644
--- a/arch/x86/kernel/acpi/cppc.c
+++ b/arch/x86/kernel/acpi/cppc.c
@@ -11,6 +11,11 @@
 
 /* Refer to drivers/acpi/cppc_acpi.c for the description of functions */
 
+bool cpc_supported_by_cpu(void)
+{
+	return boot_cpu_has(X86_FEATURE_CPPC);
+}
+
 bool cpc_ffh_supported(void)
 {
 	return true;
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index d64facbda0fb7..6ff1901d7d436 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -577,6 +577,19 @@ bool __weak cpc_ffh_supported(void)
 	return false;
 }
 
+/**
+ * cpc_supported_by_cpu() - check if CPPC is supported by CPU
+ *
+ * Check if the architectural support for CPPC is present even
+ * if the _OSC hasn't prescribed it
+ *
+ * Return: true for supported, false for not supported
+ */
+bool __weak cpc_supported_by_cpu(void)
+{
+	return false;
+}
+
 /**
  * pcc_data_alloc() - Allocate the pcc_data memory for pcc subspace
  *
@@ -686,7 +699,8 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 
 	if (!osc_sb_cppc2_support_acked) {
 		pr_debug("CPPC v2 _OSC not acked\n");
-		return -ENODEV;
+		if (!cpc_supported_by_cpu())
+			return -ENODEV;
 	}
 
 	/* Parse the ACPI _CPC table for this CPU. */
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index c6108581d97dc..d389bab54241d 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -145,6 +145,7 @@ extern bool cppc_allow_fast_switch(void);
 extern int acpi_get_psd_map(unsigned int cpu, struct cppc_cpudata *cpu_data);
 extern unsigned int cppc_get_transition_latency(int cpu);
 extern bool cpc_ffh_supported(void);
+extern bool cpc_supported_by_cpu(void);
 extern int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val);
 extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
 #else /* !CONFIG_ACPI_CPPC_LIB */
-- 
2.25.1