linux-kernel - [PATCH v2] ACPI: CPPC: Don't require _OSC if X86_FEATURE

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Date:   Wed, 29 Jun 2022 15:04:32 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     <mario.limonciello@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Len Brown" <lenb@...nel.org>, Sudeep Holla <sudeep.holla@....com>,
        Pierre Gondois <pierre.gondois@....com>
CC:     Perry Yuan <perry.yuan@....com>, <linux-acpi@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported

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 that to 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@....com>
Signed-off-by: Mario Limonciello <mario.limonciello@....com>
---
v1->v2:
 * Make the code easier to follow (suggested by Rafael)
 * Update commit message to reflect this is only fixing the MSR case
   and that any other breakage from 72f2ecb7ece7 will need additional
   follow ups
 drivers/acpi/cppc_acpi.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 903528f7e187..cc154519c608 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -629,7 +629,15 @@ static bool is_cppc_supported(int revision, int num_ent)
 		return false;
 	}
 
-	return true;
+	if (!osc_sb_cppc_not_supported)
+		return true;
+
+	pr_debug("Firmware missing _OSC support\n");
+#ifdef CONFIG_X86
+	return boot_cpu_has(X86_FEATURE_CPPC);
+#else
+	return false;
+#endif
 }
 
 /*
@@ -684,9 +692,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 	acpi_status status;
 	int ret = -ENODATA;
 
-	if (osc_sb_cppc_not_supported)
-		return -ENODEV;
-
 	/* Parse the ACPI _CPC table for this CPU. */
 	status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
 			ACPI_TYPE_PACKAGE);
-- 
2.25.1