[PATCH v6] acpi: Issue _OSC call for native thermal interrupt handling

[Srinivas Pandruvada]

There are several reports of freeze on enabling HWP (Hardware PStates)
feature on Skylake based systems by Intel P states driver. The root
cause is identified as the HWP interrupts causing BIOS code to freeze.
HWP interrupts uses thermal LVT.
Linux natively handles thermal interrupts, but in Skylake based systems
SMM will take control of thermal interrupts. This is a problem for several
reasons:
- It is freezing in BIOS when tries to handle thermal interrupt, which
will require BIOS upgrade
- With SMM handling thermal we loose all the reporting features of
Linux arch/x86/kernel/cpu/mcheck/therm_throt driver
- Some thermal drivers like x86-package-temp driver depends on the thermal
threshold interrupts
- The HWP interrupts are useful for debugging and tuning performance

So we need native handling of thermal interrupts. This requires some
way to inform SMM that OS can handle thermal interrupts. This can be
done by using _OSC/_PDC under processor scope very early in ACPI
initialization flow.
The bit 12 of _OSC/_PDC in processor scope defines whether OS supports
handling of native interrupts for Collaborative Processor Performance
Control (CPPC) notifications. Since HWP is a implementation of CPPC,
setting this bit is equivalent to inform SMM that OS is capable of
handling thermal interrupts.
Refer to this document for details on _OSC/_PDC
http://www.intel.com/content/www/us/en/standards/processor-vendor-
specific-acpi-specification.html

This change introduces a new function acpi_early_processor_set_osc(),
which walks acpi name space and finds acpi processor object and
set capability via _OSC method.

Also this change writes HWP status bits to 0 to clear any HWP status
bits in intel_thermal_interrupt().

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
---
v6:
Added __init for two functions and moved dummy function to internal.h
Shortened the name of the function.

v5:
No code change. Changed commit message to explain HWP is a implementation
of CPPC.

v4:
Suggestion by Boris for removing use of intermediate variable for
clearing HWP status and using boot_cpu_has instead of static_cpu_has

v3:
- Added CONFIG_X86 around static_cpu_has() to fix compile error on
ARCH=ia64, reported by kbuild test robot
- return AE_CTRL_TERMINATE to terminate acpi name walk space, when _OSC
is set already once.
v2:
Unnecessary newline was introduced, removed that in acpi_processor.c

 arch/x86/kernel/cpu/mcheck/therm_throt.c |  3 +++
 drivers/acpi/acpi_processor.c            | 44 ++++++++++++++++++++++++++++++++
 drivers/acpi/bus.c                       |  3 +++
 drivers/acpi/internal.h                  |  6 +++++
 4 files changed, 56 insertions(+)

diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
index 2c5aaf8..0553858 100644
--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -385,6 +385,9 @@ static void intel_thermal_interrupt(void)
 {
 	__u64 msr_val;
 
+	if (static_cpu_has(X86_FEATURE_HWP))
+		wrmsrl_safe(MSR_HWP_STATUS, 0);
+
 	rdmsrl(MSR_IA32_THERM_STATUS, msr_val);
 
 	/* Check for violation of core thermal thresholds*/
diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 6979186..ba50f46 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -491,6 +491,50 @@ static void acpi_processor_remove(struct acpi_device *device)
 }
 #endif /* CONFIG_ACPI_HOTPLUG_CPU */
 
+#ifdef CONFIG_X86
+static bool acpi_hwp_native_thermal_lvt_set;
+static acpi_status __init acpi_hwp_native_thermal_lvt_osc(acpi_handle handle,
+							  u32 lvl,
+							  void *context,
+							  void **rv)
+{
+	u8 sb_uuid_str[] = "4077A616-290C-47BE-9EBD-D87058713953";
+	u32 capbuf[2];
+	struct acpi_osc_context osc_context = {
+		.uuid_str = sb_uuid_str,
+		.rev = 1,
+		.cap.length = 8,
+		.cap.pointer = capbuf,
+	};
+
+	if (acpi_hwp_native_thermal_lvt_set)
+		return AE_CTRL_TERMINATE;
+
+	capbuf[0] = 0x0000;
+	capbuf[1] = 0x1000; /* set bit 12 */
+
+	if (ACPI_SUCCESS(acpi_run_osc(handle, &osc_context))) {
+		acpi_hwp_native_thermal_lvt_set = true;
+		kfree(osc_context.ret.pointer);
+	}
+
+	return AE_OK;
+}
+
+void __init acpi_early_processor_set_osc(void)
+{
+	if (boot_cpu_has(X86_FEATURE_HWP)) {
+		acpi_walk_namespace(ACPI_TYPE_PROCESSOR, ACPI_ROOT_OBJECT,
+				    ACPI_UINT32_MAX,
+				    acpi_hwp_native_thermal_lvt_osc,
+				    NULL, NULL, NULL);
+		acpi_get_devices(ACPI_PROCESSOR_DEVICE_HID,
+				 acpi_hwp_native_thermal_lvt_osc,
+				 NULL, NULL);
+	}
+}
+#endif
+
 /*
  * The following ACPI IDs are known to be suitable for representing as
  * processor devices.
diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index 891c42d..7e73aea 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -1005,6 +1005,9 @@ static int __init acpi_bus_init(void)
 		goto error1;
 	}
 
+	/* Set capability bits for _OSC under processor scope */
+	acpi_early_processor_set_osc();
+
 	/*
 	 * _OSC method may exist in module level code,
 	 * so it must be run after ACPI_FULL_INITIALIZATION
diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
index 1e6833a..9f34051b 100644
--- a/drivers/acpi/internal.h
+++ b/drivers/acpi/internal.h
@@ -138,6 +138,12 @@ void acpi_early_processor_set_pdc(void);
 static inline void acpi_early_processor_set_pdc(void) {}
 #endif
 
+#ifdef CONFIG_X86
+void acpi_early_processor_set_osc(void);
+#else
+static inline void acpi_early_processor_set_osc(void) {}
+#endif
+
 /* --------------------------------------------------------------------------
                                   Embedded Controller
    -------------------------------------------------------------------------- */
-- 
2.5.0