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

Mario Limonciello
2022-07-01T02:25:24Z

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@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
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