[PATCH 2/2] platform/x86/amd: hfi: Stand down when amd-pstate CAS is active

[Vishal Badole <Vishal.Badole@amd.com>]

From: Krishnamoorthi M <krishnamoorthi.m@amd.com>

When amd-pstate CAS is active, it takes ownership of per-CPU capacity
values that the scheduler uses to distinguish performance and efficiency
cores. amd-hfi manages the same scheduler state through its ranking
mechanism. Running both simultaneously would cause them to overwrite
each other's settings, leading to unpredictable task placement on hybrid
platforms.

Avoid loading amd-hfi if CAS is enabled.

Signed-off-by: Krishnamoorthi M <krishnamoorthi.m@amd.com>
---
 drivers/platform/x86/amd/hfi/hfi.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/platform/x86/amd/hfi/hfi.c b/drivers/platform/x86/amd/hfi/hfi.c
index 86a7f4332c35..b6878614e2bc 100644
--- a/drivers/platform/x86/amd/hfi/hfi.c
+++ b/drivers/platform/x86/amd/hfi/hfi.c
@@ -29,6 +29,8 @@
 
 #include <asm/cpu_device_id.h>
 
+#include <linux/amd-pstate.h>
+
 #include <acpi/pcc.h>
 #include <acpi/cppc_acpi.h>
 
@@ -536,6 +538,12 @@ static int __init amd_hfi_init(void)
 	    !cpu_feature_enabled(X86_FEATURE_AMD_WORKLOAD_CLASS))
 		return -ENODEV;
 
+	/* amd-pstate CAS owns heterogeneous core scheduling when enabled. */
+	if (amd_pstate_cas_active()) {
+		pr_debug("amd-pstate CAS is active, not loading amd-hfi\n");
+		return -ENODEV;
+	}
+
 	ret = platform_driver_register(&amd_hfi_driver);
 	if (ret)
 		pr_err("failed to register HFI driver\n");
-- 
2.34.1