linux-kernel - [PATCH] acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter

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Date: Mon, 17 Jun 2024 21:54:17 -0500
From: Aaron Rainbolt <arainbolt@...cus.org>
To: linux-acpi@...r.kernel.org, rafael@...nel.org
Cc: mario.limonciello@....com, lenb@...nel.org,
	linux-kernel@...r.kernel.org, mmikowski@...cus.org
Subject: [PATCH] acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter

acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter

The _OSC is supposed to contain a bit indicating whether the hardware
supports CPPC v2 or not. This bit is not always set, causing CPPC v2 to
be considered absent. This results in severe single-core performance
issues with the EEVDF scheduler.

To work around this, provide a new kernel parameter,
"processor.ignore_osc_cppc_bit", which may be used to ignore the _OSC
CPPC v2 bit and act as if the bit was enabled. This allows CPPC to be
properly detected even if not "enabled" by _OSC, allowing users with
problematic hardware to obtain decent single-core performance.

Tested-by: Michael Mikowski <mmikowski@...cus.org>
Signed-off-by: Aaron Rainbolt <arainbolt@...cus.org>

---

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 1d857978f5f4..53406dd6cb87 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -671,7 +671,7 @@ static inline void arch_init_invariance_cppc(void) { }
  *
  *	Return: 0 for success or negative value for err.
  */
-int acpi_cppc_processor_probe(struct acpi_processor *pr)
+int acpi_cppc_processor_probe(struct acpi_processor *pr, bool ignore_osc_cppc_bit)
 {
 	struct acpi_buffer output = {ACPI_ALLOCATE_BUFFER, NULL};
 	union acpi_object *out_obj, *cpc_obj;
@@ -686,7 +686,7 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 
 	if (!osc_sb_cppc2_support_acked) {
 		pr_debug("CPPC v2 _OSC not acked\n");
-		if (!cpc_supported_by_cpu()) {
+		if (!ignore_osc_cppc_bit && !cpc_supported_by_cpu()) {
 			pr_debug("CPPC is not supported by the CPU\n");
 			return -ENODEV;
 		}
diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
index 67db60eda370..a183bca6c1c5 100644
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -33,6 +33,11 @@ MODULE_AUTHOR("Paul Diefenbaugh");
 MODULE_DESCRIPTION("ACPI Processor Driver");
 MODULE_LICENSE("GPL");
 
+static bool ignore_osc_cppc_bit = false;
+module_param(ignore_osc_cppc_bit, bool, 0);
+MODULE_PARM_DESC(ignore_osc_cppc_bit,
+	"Ignore _OSC CPPC bit, assume CPPC v2 is present");
+
 static int acpi_processor_start(struct device *dev);
 static int acpi_processor_stop(struct device *dev);
 
@@ -170,7 +175,7 @@ static int __acpi_processor_start(struct acpi_device *device)
 	if (pr->flags.need_hotplug_init)
 		return 0;
 
-	result = acpi_cppc_processor_probe(pr);
+	result = acpi_cppc_processor_probe(pr, ignore_osc_cppc_bit);
 	if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
 		dev_dbg(&device->dev, "CPPC data invalid or not present\n");
 
diff --git a/include/acpi/processor.h b/include/acpi/processor.h
index 3f34ebb27525..79fd61b3f537 100644
--- a/include/acpi/processor.h
+++ b/include/acpi/processor.h
@@ -358,10 +358,10 @@ int acpi_map_cpuid(phys_cpuid_t phys_id, u32 acpi_id);
 int acpi_get_cpuid(acpi_handle, int type, u32 acpi_id);
 
 #ifdef CONFIG_ACPI_CPPC_LIB
-extern int acpi_cppc_processor_probe(struct acpi_processor *pr);
+extern int acpi_cppc_processor_probe(struct acpi_processor *pr, bool ignore_osc_cppc_bit);
 extern void acpi_cppc_processor_exit(struct acpi_processor *pr);
 #else
-static inline int acpi_cppc_processor_probe(struct acpi_processor *pr)
+static inline int acpi_cppc_processor_probe(struct acpi_processor *pr, bool ignore_osc_cppc_bit)
 {
 	return 0;
 }