Subject: Re: [PATCH v4] acpi: Issue _OSC call for native thermal interrupt
 handling
To: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        rjw@rjwysocki.net
References: <1458239047-14259-1-git-send-email-srinivas.pandruvada@linux.intel.com>
 <56EB0D81.1050900@hpe.com> <1458246992.3861.23.camel@linux.intel.com>
Cc: tony.luck@intel.com, bp@alien8.de, tglx@linutronix.de, mingo@redhat.com,
        hpa@zytor.com, lenb@kernel.org, linux-edac@vger.kernel.org,
        linux-kernel@vger.kernel.org
From: Linda Knippers <linda.knippers@hpe.com>
Message-ID: <56EB18B9.7070009@hpe.com>
Date: Thu, 17 Mar 2016 16:51:05 -0400
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On 3/17/2016 4:36 PM, Srinivas Pandruvada wrote:
> On Thu, 2016-03-17 at 16:03 -0400, Linda Knippers wrote:
>> On 3/17/2016 2:24 PM, Srinivas Pandruvada wrote:
>>>
>>> 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. 
>> Is this working around a firmware bug?
> Yes. But Linux always had capability to handle thermal interrupts
> natively, so we should continue to have this in OS control, when
> possible.
> 
>>
>>>
>>> To inform SMM that
>>> OS will handle thermal interrupts, we need to use _OSC under
>>> processor
>>> scope very early in ACPI initialization flow. 
>> Does _OSC say that OS "will" handle thermal interrupts or that it
>> "can"
>> handle thermal interrupts?
> 
> Can handle.
> 
>>   Couldn't a platform decide it wants to handle
>> them, regardless of what the OS may be capable of?
>>
> Yes. In that case platform can change the delivery mode bits to SMM in
> LVT.

And would still exhibit the BIOS bug?

>>>
>>> This needs to be done
>>> before SMM code path looks for _OSC capabilities. The bit 12 of
>>> _OSC in processor scope defines whether OS will handle thermal
>>> interrupts.
>>> When bit 12 is set to 1, OS will handle thermal interrupts.
>>> Refer to this document for details on _OSC
>>> http://www.intel.com/content/www/us/en/standards/processor-vendor-
>>> specific-acpi-specification.html
>> Where is bit 12 documented?
>>
> In the above document.

When I look at that document, I see bit 12 described as
"If set, OSPM supports native interrupt handling for Collaborative Processor
Performance Control notifications."  Is that the same thing or am
I looking at the wrong table?

-- ljk

> 
>>>
>>> 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 to take over thermal LVT.
>> Does this change just affect Skylake platforms or all platforms?
> Any platform which has Intel ® Speed Shift Technology (aka HWP) feature
> present and enabled.
> 
> Thanks,
> Srinivas 
> 
>>
>> -- ljk
>>>
>>>
>>> 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@linux.intel
>>> .com>
>>> ---
>>> 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            | 47
>>> ++++++++++++++++++++++++++++++++
>>>  drivers/acpi/bus.c                       |  3 ++
>>>  drivers/acpi/internal.h                  |  2 ++
>>>  4 files changed, 55 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..18da84f 100644
>>> --- a/drivers/acpi/acpi_processor.c
>>> +++ b/drivers/acpi/acpi_processor.c
>>> @@ -491,6 +491,53 @@ 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 acpi_set_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 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_set_hwp_native_thermal_lv
>>> t_osc,
>>> +				    NULL, NULL, NULL);
>>> +		acpi_get_devices(ACPI_PROCESSOR_DEVICE_HID,
>>> +				 acpi_set_hwp_native_thermal_lvt_o
>>> sc,
>>> +				 NULL, NULL);
>>> +	}
>>> +}
>>> +#else
>>> +
>>> +void acpi_early_processor_set_osc(void) {}
>>> +
>>> +#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..5c787ac 100644
>>> --- a/drivers/acpi/internal.h
>>> +++ b/drivers/acpi/internal.h
>>> @@ -138,6 +138,8 @@ void acpi_early_processor_set_pdc(void);
>>>  static inline void acpi_early_processor_set_pdc(void) {}
>>>  #endif
>>>  
>>> +void acpi_early_processor_set_osc(void);
>>> +
>>>  /* -------------------------------------------------------------
>>> -------------
>>>                                    Embedded Controller
>>>     ---------------------------------------------------------------
>>> ----------- */
>>>