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Date: Thu, 17 Mar 2016 13:36:32 -0700
From: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To: Linda Knippers <linda.knippers@....com>, rjw@...ysocki.net
Cc: tony.luck@...el.com, bp@...en8.de, tglx@...utronix.de,
mingo@...hat.com, hpa@...or.com, lenb@...nel.org,
linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] acpi: Issue _OSC call for native thermal interrupt
handling
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.
> >
> > 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.
> >
> > 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@...ux.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
> > ---------------------------------------------------------------
> > ----------- */
> >
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